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Why Do I Have Strong Body Odor?

Causes and how to get rid of strong body odor

• Causes of Strong Body Odor
• Reducing Strong Body Odor
• Medical Treatments

Body odor (BO) is a normal part of being human. Hormones, certain medical conditions, and the food you eat can cause strong body odor or changes in the way that you smell. Strong body odor is often perceived as being unpleasant, but there are ways to prevent or treat BO.  This article discusses the causes of strong body odor, tips for reducing it, and medical treatments for body odor that doesn’t improve with preventative measures.

Verywell / Brianna Gilmartin

What Causes Strong Body Odor?

Sweat itself doesn't have a smell. Body odor comes from the bacteria that live on sweaty parts of your body, like your armpits. When you sweat, these bacteria break down certain proteins in your sweat into acids, causing an odor.

Whether your sweat causes body odor depends on the glands releasing it. You're more likely to have body odor when your sweat comes from apocrine glands, which release sweat from hair follicles found in the armpits, groin, and pubic area. Sweat from these glands, produced when you're hot or stressed, contain fats and other compounds that smell when broken down by bacteria.

Eccrine glands, on the other hand, are found all over your skin and squeeze out sweat through a duct to regulate your body temperature. This sweat lacks the fats and other compounds that can smell when broken down by bacteria.

Additional external factors can also contribute to how you smell.

Weight Changes

When you gain weight, you may develop more skin folds. These folds can hold sweat and bacteria, which create ideal conditions for strong body odor.

Onions, garlic, and some cruciferous vegetables contain sulfur, which can build up and come out through eccrine sweat glands, making body odor even stronger.

Spicy foods can also make you sweat more, which in turn can give you a stronger scent.

Medical Conditions

Some conditions can change your normal body scent. These include diabetes , kidney problems or liver disease, and an overactive thyroid . Some very rare genetic conditions can also change your body's odor.

In some cases, an odd body odor can be a sign of something more serious. For example, a bleach-like or urine-like smell may indicate kidney or liver problems.

Stress increases your heart rate and sends a signal to your sweat glands to begin producing sweat to help regulate your body temperature and balance your body's fluids. While sweat may be released through the eccrine glands, most stress-induced sweat will come out of the apocrine glands, which create smellier sweat.

So, you may notice an increase in body odor right before or during a stressful event.

If your family members have smellier sweat, you may be more likely to have it, too. Genes are one of the factors that determine your individual odor.

Excessive Sweating

A condition called hyperhidrosis can cause you to sweat a lot . People with this condition may sweat even when they don't feel excessively hot or stressed.

Menopause may also cause an increase in sweat due to changes in hormone levels that affect your body's ability to regulate temperature. And some people just naturally sweat more than others.

Hormones (Pregnancy or Puberty)

Shifting hormones during pregnancy can raise your body temperature and can make your body think it's hotter than it actually is. The combination can cause you to sweat more than usual, leading to body odor.

Puberty is another time when people may have more body odor than usual. That's because the surge in hormones makes sweat glands more active, allowing for the kind of sweating that causes BO.

How to Get Rid of Strong Body Odor

Body odor can be embarrassing. Fortunately, in most cases, it doesn't signal a serious problem. There are things you can do to banish body odor, or at least tone it down.

Shower Daily

Shower at least once a day. Use soap or shower gel and lather up thoroughly. Pay special attention to the areas prone to body odor.

If you are in a very hot or humid area, you may need to shower twice a day. You can also use a washcloth to wash just your armpits, groin, and skin folds. Be sure to shower immediately after you exercise or sweat.

Use Anti-Bacterial Soap

If regular showers don't seem to help, try a special cleanser. These include:

• Anti-bacterial soap or body wash like Dial
• Benzoyl peroxide cleanser

These washes can help reduce the amount of bacteria on your skin.

Choose the Right Underarm Products

There are two types of underarm products: deodorants and antiperspirants.

Deodorants make your underarms less hospitable for bacteria. They also help mask body odor with a fragrance. Antiperspirants block sweat glands to reduce perspiration.

If you don't sweat much but still get body odor, deodorants are a good choice. If you sweat a lot, look for a product that is both an antiperspirant and a deodorant.

If you have strong body odor, look for a product with higher amounts of active ingredients. If over-the-counter products don't seem to help, talk to a healthcare provider. You might benefit from a prescription antiperspirant/deodorant .

Wear Breathable Fabrics

Natural fabrics like cotton are better than polyester, nylon, and rayon at controlling body odor. Natural fibers breathe; this lets sweat evaporate.

Avoid fabrics that trap sweat against the skin. These create a better breeding ground for body odor. When working out, choose moisture-wicking fabrics.

Change Your Diet

Remove or reduce spicy or pungent foods from your diet. This includes foods like:

• Spicy peppers
• Brussels sprouts

These foods can cause a more pungent sweat. Even alcohol can change the smell of your sweat.

If you eat these types of foods regularly, try eating less of them or stop eating them altogether. This might help improve your body odor.

Shave or Wax

Apocrine glands are concentrated in areas covered by hair. This includes the armpits and the pubic area.

Hair holds sweat and makes a good home for bacteria. Removing hair can help control body odor.

Consider shaving your underarms. If you'd rather not go bare, try trimming the hair short. This can also help reduce body odor.

Medical Treatments for Body Odor

If you've tried these tips and haven't seen an improvement, call a healthcare provider. Something else may be causing your body odor, such as a fungal infection. Or, you just may need a stronger treatment.

Consider these options:

• Prescription antiperspirants/deodorants are stronger than what you can get over the counter. These are usually the first treatment step for body odor.
• Antibiotics , either topical or oral, can help reduce bacteria on the skin.
• Botox (onabotulinumtoxin A) injections can reduce your sweat glands' ability to produce sweat. This is not a permanent fix, though. Treatment needs to be repeated every few months.
• Laser treatment reduces hair follicles. This may not help with body odor, though.
• Surgery to remove sweat glands can be done in extreme cases.

Body odor is caused by bacteria breaking down the sweat from the apocrine glands in your armpits, groin, and pubic area. 

You may be more prone to body odor if you are overweight, eat certain foods, have certain health conditions, or are under stress. Genetics may also play a role.

You can prevent body odor with lifestyle changes like daily showering and choosing the right underarm product.

If you still have body odor after trying these things, ask a healthcare provider about prescription medication or medical procedures that might help.

Hamada K, Haruyama S, Yamaguchi T, et al. What determines human body odour ? Exp Dermatol. 2014;23(5):316-7. doi:10.1111/exd.12380

Harvard Health Publishing. What's that smell? Get rid of body odor .

International Hyperhidrosis Society. 6 ways to control stress sweat .

Callewaert C, De Maeseneire E, Kerckhof FM, Verliefde A, Van de Wiele T, Boon N. Microbial odor profile of polyester and cotton clothes after a fitness session .  Appl Environ Microbiol . 2014;80(21):6611–6619. doi:10.1128/AEM.01422-14

Chen W, Zhang X, Zhang L, Xu Y. Treatment of axillary bromhidrosis in adolescents by combining electrocauterization with ultrasound-guided botulinum toxin type A injection . J Plast Reconstr Aesthet Surg. 2021;S1748-6815(21)00193-5. doi:10.1016/j.bjps.2021.03.089

Pastor DK, Harper DS. Treating body odor in primary care . Nurse Pract . 2012;13;37(3):15-8. doi:10.1097/01.NPR.0000409913.95393.28

By Angela Palmer Angela Palmer is a licensed esthetician specializing in acne treatment.

ORIGINAL RESEARCH article

Children’s body odors: hints to the development status.

• 1 Department of Psychotherapy and Psychosomatic Medicine, Technische Universität Dresden, Dresden, Germany
• 2 Institute of Psychology, University of Wrocław, Wrocław, Poland

Mothers can recognize their own children by body odor. Besides signaling familiarity, children’s body odors may provide other information relevant to maternal caregiving behavior, such as the child’s developmental status. Thus, we explored whether mothers are able to classify body odors on pre- vs. postpubertal status above chance levels. In total, 164 mothers were presented with body odor samples of their own and four unfamiliar, sex-matched children who varied in age (range 0–18 years). Pubertal status was measured by (a) determining the child’s steroid hormone level and (b) parental assessment of the child’s developmental stage using the Pubertal Development Scale. Mothers classified developmental status with an accuracy of about 64%. Maternal assessments were biased toward pre-puberty. Classification was predicted by perceptual evaluation of the body odor (i.e. intensity and pleasantness) and by the child’s developmental stage, but not by hormones. In specific, mothers with pubertal-aged children classified body odors using the child’s developmental status, whereas mothers with younger children only classified body odors using perceptual information (i.e. intensity and pleasantness). Our data suggests that body odors convey developmental cues, but how this developmental information is manifested in body odor remains unclear.

Introduction

Body odors are a potent chemosignal in human social communication for two reasons. First, they allow recognition of the own relative among a number of individuals ( Pause et al., 1998 ; Lundström et al., 2009 ). Second, both hedonic [i.e. pleasantness or attractiveness, ( Kuukasjärvi et al., 2004 ; Croy et al., 2017 )] ratings and neural activity ( Cecchetto et al., 2019 ) support the idea that body odors communicate affective information to recipients. Both of these features of body odors are highly relevant in the context of mother–child bonding. In specific, kin recognition serves to facilitate a targeted investment of resources ( Burnstein et al., 1994 ; Chapais et al., 2001 ), which is important for providing one’s offspring with care. With regard to the affective value, in a previous study asking for parental perception of their children’s body odors, we found that a baby’s body odor was perceived as highly adorable and pleasant ( Croy et al., 2017 ). In addition, mothers respond to infant’s body odors with neural activation in reward-related processing areas [e.g. neostriate areas ( Lundström et al., 2013 )]. The authors concluded that the infantile odor may evoke a desire to bond in parents.

Kin recognition has been demonstrated in response to infants, preschool, and adolescent children ( Porter et al., 1983 ; Weisfeld et al., 2003 ; Ferdenzi et al., 2010 ). Besides, recognition and a mother’s preference for the body odor of her own child seem to affect each other. For example, mothers who are not able to recognize their own child’s body odor do not show a preference for their child’s odor. Consistent with this, Croy et al. (2019) showed that mothers with postpartum bonding disorders had a lower preference for their own child’s body odor, compared to healthy controls. Further, in a recent study conducted in our lab, we presented 164 healthy mothers to body odor probes of their own and sex-matched unfamiliar children in different age groups, from infancy to adulthood ( Schäfer et al., in press ). Interestingly, the relationship between source of the body odor (i.e. child vs. other) and odor preference in mothers, varied across the child’s development – i.e. mothers preferred their own child’s odor when the child was pre- or postpubertal, but not when the child was in early puberty. In that stage, the decrement in maternal pleasantness ratings of their son’s body odor was associated with increasing testosterone levels in their sons. In addition, mothers were not able to identify their own child’s body odor around puberty but were able to do so in pre- and late pubertal stages. Such findings, led to two suppositions; (1) that the loss of kin recognition with initial hormonal release around puberty is causal for a mother’s lack of preference to her child’s body odor and (2) that kin recognition and preference of the odor recover over time, because mothers get used to (i.e. are able to identify) the odor again.

In general, developmental cues are necessary for signaling a certain stage of maturity, which affects the amount and the manner of caregiving exerted by parents on their children. Several infantile facial characteristics facilitate a perception of cuteness, and thus elicit approach and attachment behavior ( Kringelbach et al., 2016 ). Those features are lost with increasing development status and in the same time willingness for parental investment declines ( Volk et al., 2007 ). In the domain of olfaction, similar mechanisms may be present.

In order to serve as a developmental cue, it is a prerequisite that body odors change during development. These changes are presumably due to developmental hormones. We base this assumption on the observation that female body odors smell different across the menstrual cycle. In specific, men rate female body odors as more pleasant during ovulation ( Havlíček et al., 2017 ), and this preference is disturbed by women’s hormonal contraceptive use ( Kuukasjärvi et al., 2004 ). The particular hormones that mediate this alteration in odor preference across the menstrual cycle are yet to be identified but steroid hormones may be a likely candidate. Steroid hormones seem to affect body odor perception – for example, higher estradiol concentration is associated with higher attractiveness of female body odor ( Lobmaier et al., 2018 ), whereas male body odor contains more androgen-derived steroids and is perceived as more intense ( Sergeant, 2010 ). The relation to actual testosterone levels has however been unclear ( Rantala et al., 2006 ).

As short-term hormonal fluctuations, such as those present during the menstrual cycle, are perceivable via body odor, we also assume that slow, long-term changes of hormonal and pubertal development from infancy (prepubertal stage) to adulthood (postpubertal stage) is reflected in body odor perception. Support for this supposition comes from a questionnaire study asking for parent’s evaluation of their children’s body odors across development ( Croy et al., 2017 ). Parents reported less pleasantness of odors from their pubertal compared to younger children, which might mirror the increase of steroid hormones during that period.

Puberty is characterized by two main stages of development – the first stage, adrenarche, occurs between the age of 5 and 9 years and is characterized by arise of androgens without leading to visible changes. Children in that phase are still referred to as prepubertal. The second stage, gonadarche, begins between 9 and 11 years and is marked by testosterone and estradiol increase. During that phase, primary and secondary sexual features develop, peaking with transition to adulthood ( Dorn et al., 2006 ).

The present study aimed to address whether body odors function as an indicator for development and explored the ability of mothers to identify a child’s developmental stage, using body odor. We hypothesized that mothers are able to accurately distinguish pre- from postpubertal odors (H1). Further, we assumed that this ability depends on developmental familiarity of the mothers: a mother of a prepubertal child might be particularly good at accurately detecting prepubertal status in body odor, whereas a mother of a postpubertal child might be better able to classify postpubertal body odors (H2). Finally, we explored potential mechanisms (maternal perceptual ratings, hormonal and developmental status of the child) contributing to developmental classification of body odor (H3).

Materials and Methods

The study was approved by the Ethics Committee of the University of Dresden (Code: EK 104032015), and all participants provided written, informed consent in accordance with the Declaration of Helsinki. The study was part of a broader project assessing maternal kin recognition and hedonic evaluation of children’s body odors (including the dimensions sweetness, wanting, and attraction) in relation to genetic analysis of the human leukocyte antigen complex. In order to facilitate readability, we omit from presenting the whole study here and focus on presentation of parts relevant for the current research question. For all further information, please compare ( Schäfer et al., in press ).

Participants

The sample consisted of N = 164 mothers ( M = 37.5, SD = 7.8) with N = 226 children ( M = 7.6, SD = 5.9 years, n = 124 girls, n = 102 boys), of whom 226 BO probes were sampled. Inclusion criteria was being the biological mother of a child between 0 and 18 years of age. Current pregnancy, insufficient knowledge of German language and anosmia or hyposmia were exclusion criteria. Olfactory performance was assessed prior to study inclusion with a short version of the standardized Sniffin Stick’s Step II ® screening for olfactory identification ability ( Lötsch et al., 2016 ). In addition, prior to the experiment mothers were asked if they had acute rhino-sinonasal disorders (which could impair olfactory abilities), and were postponed to a later date if they reported having so.

Study Procedure

Participants came to an initial meeting in the lab of the Department of Psychosomatics at the University Hospital Dresden, in which the study procedure was explained and inclusion and exclusion criteria were tested. After meeting those criteria, participants were equipped with a study kit for sampling the body odors and hormonal status of their children at home.

The study kit included odorless shower gel, odorless detergent, a salivette (Salivette ® , code blue, SARSTEDT AG & Co. KG, Nümbrecht, Germany), an unworn 100% cotton t-shirt or onesie in the respective size of the child, a re-closeable plastic zip bag, and a study protocol. In order to minimize potential sources of smell, the garment had been washed by the experimenter with an odorless detergent. The protocol contained detailed instructions for body odor and hormonal sampling, and also screened for potential confounders of the body odor sample – i.e. the presence of contamination of the sample (e.g. urine or feces), the medical condition of the child (use of drug and current illness), and the situation at home (smoking, pets, and number of persons who sleep in the children’s room).

BO Sampling

The children slept for one night in the garment. Prior to that, parents were instructed to wash sheets and clothes additionally worn to the garment with odorless detergent (Denkmit Vollwaschmittel Ultra Sensitive, dm-drogerie markt GmbH & Co. KG, Karlsruhe, Germany 1 ) and the children were asked to shower with the odorless shower gel (both EUBOS flüssig wasch+dusch, Dr. Hobein GmbH, Meckenheim, Germany 2 ), as well as to refrain from usage of any perfumed hygiene products. After wearing the garment for one night, the sample was stored in a re-closeable plastic zip bag and brought back to the lab by the parents the next morning, which was where the sample was cut in half and then frozen (−25°C) until the experiment was carried out.

Hormonal Sampling and Assessment of Development Status

For all children aged between 5 and 18 years, hormonal sampling and maternal assessment of the pubertal status using the Pubertal Development Scale [PDS, ( Watzlawik, 2009 )] was performed. Hormonal sampling was carried out in the evening before the experimental night in order to measure hormonal status in direct relation to the body odor sample. Mothers were instructed to explain their children to chew for 60 s on the salivette until it contained sufficient saliva. Overnight, the salivette was stored in the fridge and the next morning, saliva and body odor sample were taken to the lab where they were frozen at −25°C until analyses. Hormonal analysis was carried out by the Dresden LabService GmbH. For each sample, testosterone and estradiol concentration was determined via immune-assay analyses as follows ( Rohleder et al., 2006 ).

Concentration of alpha-amylase in saliva was measured by an enzyme kinetic method: saliva was processed on a Genesis RSP8/150 liquid handling system (Tecan, Crailsheim, Germany). First, saliva was diluted 1:625 with double-distilled water by the liquid handling system. Twenty microliters of diluted saliva and standard were then transferred into standard transparent 96-well microplates (Roth, Karlsruhe, Germany). Standard was prepared from “Calibrator f.a.s.” solution (Roche Diagnostics, Mannheim, Germany) with concentrations of 326, 163, 81.5, 40.75, 20.38, 10.19, and 5.01 U/l alpha-amylase, respectively, and bidest water as zero standard. After that, 80 ml of substrate reagent (α-amylase EPS Sys; Roche Diagnostics, Mannheim, Germany) were pipetted into each well using a multichannel pipette. The microplate containing sample and substrate was then warmed to 37°C by incubation in a water bath for 90 s. Immediately afterward, a first interference measurement was obtained at a wavelength of 405 nm using a standard ELISA reader (Anthos Labtech HT2, Anthos, Krefeld, Germany). The plate was then incubated for another 5 min at 37°C in the water bath, before a second measurement at 405 nm was taken. Increases in absorbance were calculated for unknowns and standards. Increases of absorbance of diluted samples were transformed to alpha-amylase concentrations using a linear regression calculated for each microplate (GraphPad Prism 4.0c for MacOSX, GraphPad Software, San Diego, CA). The intra- and interassay coefficients for amylase were below 9 and 9%,respectively. The detection threshold for the analyzed samples was at 0.3 pg/ml for estradiol and at 1.8 pg/ml for testosterone.

Mothers completed the PDS ( Watzlawik, 2009 ) which is a standardized assessment of pubertal status with sufficient reliability ( r = 0.64–0.69) and validity (self- vs. external assessment, r = 0.39 and 0.83) ( Watzlawik, 2009 ). The PDS comprises three questions for each boys and girls (development of body hair, growth of breast/beard, menarche, and voice break) which are summed up to a score indicating pubertal status (ranging from 3 = puberty has not begun) to 12 (development completed). According to the manual ( Crockett and Petersen, 1987 ; Crockett, 1988 ; Carskadon and Acebo, 1993 ), the following categories were defined as indicators for the pubertal status of boys: prepubertal (3 points), early pubertal (4 or 5 points), midpubertal (6, 7, or 8 points), late pubertal (9–11 points), and postpubertal (12 points) status. For girls the classification was: prepubertal (2 and no menarche), early pubertal (3 and no menarche), midpubertal (>3 and no menarche), late pubertal (<7 and menarche), and postpubertal (8 and menarche) status.

Experimental Procedure

One and half hours before the experimental session, body odor samples were thawed. Subjects were asked to refrain from eating, drinking coffee, and smoking 1 h prior to the testing, as well as from usage of perfume on the study day. The experimenter refrained from usage of perfume and wore rubber gloves in order to not confound the odor of the samples.

In total, the mothers assessed six body odor samples including the body odor of the own child and four body odor probes of unfamiliar children, as well as an unworn blank probe (previously washed with the odorless detergent) to control for intensity of the body odor samples. The unfamiliar children were matched to the same sex as the own child and two different age groups (two children of the same age group as the own child, two children of a different developmental group; i.e. a prepubertal age group when the own child was postpubertal, and vice versa).

For body odor presentation, the experimenter instructed the subject to close the eyes during 6 s of smelling in order to focus on the smell and to not be biased by seeing if the sample belonged to a t-shirt or to a onesie. The sample was placed by the experimenter directly under the nose of the participants, with the armpit pad upward. After 6 s, the probe was placed back and the subject had to open her eyes and to rate the body odor.

Prior to the rating procedure, body odors were presented in a test trial without assessment of the probes. This was done in order to anchor the probes for intensity. The six samples were then rated on pleasantness and intensity using visual analogue scale (VAS), ranging from 0 (“not at all”) to 100 (“very”). Afterward, mothers rated the age group of the body odor donor. Therefore, the subjects were instructed to choose one of the following categories for each sample: “<1 year,” “1–3 years,” “4–8 years,” “9–13 years,” “14–18 years,” and “>18 years.”

Statistical Analyses

All statistical analyses were performed with IBM SPSS Statistics 25 ( IBM Corp, 2017 ).

For analyses, three age categories [based off Dorn et al. (2006) ] were created to indicate the child’s developmental status. These were as follow – prepubertal (0–8 years), midpubertal (9–13 years), and postpubertal (≥14 years). This grouping was confirmed by the prior assessed PDS categories. Almost all (126 out of 128, 98.4%) children aged 0–8 years had a PDS score which indicated prepuberty and 50 out of 55 (90.9%) of the children aged 14–18 years had a PDS score which indicated a late or postpubertal stage. We decided to exclude body odor probes of those seven children whose age groups did not align with the PDS for statistical analysis of H1 and H2. We also decided to exclude body odor probes of the n = 42 midpubertal children (9–13 years), as this group comprised children of heterogeneous developmental status at the transition between pre- to postpubertal status, and therefore was not suitable to be classified in one consistent stage (see Table 1 ).

Table 1. Frequencies of all presented body odor samples classified by PDS category and age group.

This procedure led to a final sample size of 177 body odor probes for analysis of H1 and H2. As each mother rated multiple body odor samples, this resulted in 890 maternal assessments of developmental stage. For analyzing H3, we used the total sample of 226 body odor probes (=1127 assessments).

All analyses were carried out (a) for all children and (b) only for unfamiliar children excluding the own child’s body odor sample from analyses. This additional analysis was done in order to not bias performance due to recognition of the own child’s odor and thus assuming to know the age. For reasons of clearness, only analyses for all children are presented here. Results regarding the unfamiliar children are listed in the Supplementary Material (see Supplementary Figures 3–5 and Supplementary Tables 1–3 ).

Mothers are able to accurately distinguish pre- from post-pubertal odors (H1); classification ability depends on developmental familiarity of the mothers (H2)

We first assessed whether there was a significant difference of maternal classification in children of prepubertal vs. postpubertal stage using χ 2 test. Subsequently, we tested the sensitivity, specificity and accuracy of classification. Therefore, all maternal answers were categorized in one 4-field matrix for each developmental status, and this was based on their accuracy. The four categories are as follow – (1) a true positive (tp) or hit was assigned in case of correct detection of the developmental status, (2) a true negative (tn) was assigned when a mother correctly rejected the developmental status (e.g. not choosing prepubertal for a postpubertal body odor), (3) a false positive (fp) was assigned when a postpubertal sample was rated as prepubertal (or vice versa), and (4) a false negative (fn) was assigned, when a body odor sample was not detected as pre- or postpubertal even though it was pre-/postpubertal. We calculated sensitivity, specificity, and accuracy of the maternal classification for each developmental status. Additionally, we calculated the RATZ-index indicating how much the maternal hit rate increases compared to the chance level [relative increase of the hit rate compared to the random hit rate ( Marx and Lenhard, 2010 )]. The index can take values between 0 and 1, with values from 0.3 being seen as an improvement to the random rate.

In order to explore the impact of maternal developmental familiarity, we compared for each mother the classification of those body odor samples which had the same developmental status as the own child (developmental familiar classification) to the classification of those body odor samples which had a different developmental status as the own child (developmental unfamiliar classification). Classification performance across the groups was compared using a 4 × 2 χ 2 test calculator 3 .

We tested the influence of hormonal contraceptive use on maternal classification performance, as this has been previously reported to influence olfactory perception ( Derntl et al., 2013 ). On the day of testing, 38.5% of the mothers stated to use hormonal contraception, 54% stated not to use hormonal contraception, and 7.5% did not reply to this question. Comparison between the groups revealed no significant differences between the groups [χ 2 (1) = 5.70, p = 0.127], which is why we did not include this in further analyses. We also compared maternal classification performance for boys and girls within each developmental status, and found no significant differences [prepubertal classification: χ 2 (1) = 3.65, p = 0.057; postpubertal classification: χ 2 (1) = 0.10, p = 0.757]. Therefore, we did not perform any further sex-specific analyses.

Predictors of pre- vs. postpubertal body odor classification (H3)

For H3, logistic regression analyses including bootstrapping ( n = 1000) were performed with the binary outcome of pre- vs. postpubertal maternal classification as dependent variable.

As predictors we modeled perceptual evaluation of the body odor (pleasantness and intensity) in order to assess the influence of affective perception on the classification. For exploring the influence of developmental cues on body odor classification, the PDS score and hormonal status (comprising the testosterone status for boys and the estradiol status for girls in pg/ml) were included as further predictors. All predictors were tested in one model using enter method.

All analyses were performed across all children and all mothers and then for developmental familiar samples and developmental unfamiliar samples separately.

Mothers Are Able to Accurately Distinguish Pre- From Post-pubertal Odors (H1)

When presented to body odors of prepubertal children, mothers stated in 71.6% of the cases that those odors were from a prepubertal donor and in 28.17% that these odors were from a postpubertal donor. When presented to body odors of postpubertal children, mothers stated in 58.6% of the cases that those odors were from a prepubertal donor and in turn, mothers stated in 41.4% of the cases that the odors were from a postpubertal donor (see Figure 1 ). The classification of an odor as postpubertal was significantly higher when mothers were presented to postpubertal odors than when they were presented to prepubertal odors [χ 2 (1) = 10.82, p = 0.001]. Furthermore, this result reveals that BOs are more frequently rated as originating from a prepubertal than from a postpubertal donor.

Figure 1. Left panel: classification performance: (A) percentage of the sensitivity of maternal classification plotted by PDS categories; (B) percentage of frequency of true positives (tp), false positives (fp), false negatives (fn), and true negatives (tn) plotted in blue for prepubertal and in read for postpubertal body odors. Color intensity indicates frequency of choice. Right panel: classification predictors: (C) perceptual predictors (above: pleasantness, below: intensity); (D) developmental predictors [above: pubertal development scale (PDS), below: hormonal concentration in pg/ml, estradiol for girls, testosterone for boys]. Assessment of developmental predictors was carried out for all children from the age of 5 years on and therefore children under the age of 5 exhibit a value of 3 for the PDS (prepubertal) and a value of 0 for the hormonal concentration.

The detection of prepubertal odors was performed with an accuracy of 63%. This value exceeds the 50% chance level. However, the RATZ-index of 0.11 is rather low and suggests that mothers do not perform substantially better than chance. Maternal assessments of prepubertal odors had a sensitivity of 72.0% and a specificity of only 38.7%, indicating that maternal assessments tended to accept the classification of a sample as prepubertal [χ 2 (1) = 472.63, p < 0.001].

A similar effect was found for postpubertal body odors, which were detected with an accuracy of 64.0% at an RATZ-index of 0.14. Maternal assessments of postpubertal odors had a sensitivity of only 41.4% and a specificity of 71.2%, indicating that maternal assessments tended to reject the classification of a sample as postpubertal.

Classification Ability Depends on Developmental Familiarity of the Mothers (H2)

Separate analyses of developmental familiar samples and developmental unfamiliar samples revealed that mothers were more accurate in classifying body odors of donors at the same developmental status as their own child (see Supplementary Figures 1 , 2 ).

Hence, mothers of prepubertal children could identify prepubertal odors with a higher accuracy of 65.2% (RATZ-index = 0.19; sensitivity = 74.4%; specificity = 43.8%) compared to the 60.6% accuracy of mothers having postpubertal children (RATZ-index: 0.04%; sensitivity = 67.7%; specificity = 35.7%). The difference between maternal classification of developmental familiar samples and developmental unfamiliar samples was significant [χ 2 (1) = 9.84, p = 0.020].

Similarly, mothers of postpubertal children were more accurate in classification of postpubertal body odors (developmental familiar samples: accuracy = 65.2%; RATZ-index: 0.19; sensitivity = 43.2%; specificity = 73.6%; developmental unfamiliar samples: accuracy = 62.2%; RATZ-index: 0.07%; sensitivity = 37.7%; specificity = 68.1%) and maternal classification differed significantly between both groups [developmental familiar samples vs. developmental unfamiliar samples: χ 2 (1) = 8.95, p = 0.029].

Predictors of Pre- vs. Postpubertal BO Classification (H3)

The overall regression model across all mothers was significant [χ 2 (4) = 79.98, p < 0.001], revealing that pleasantness ( p < 0.001), intensity ( p < 0.001), and pubertal status (PDS score, p = 0.007) predicted developmental classification, while hormones did not relate to maternal decision ( p = 0.952, see Table 2 ). In particular, higher pleasantness predicted prepubertal classification, whereas higher intensity and higher pubertal status were associated with postpubertal classification (see Figure 1 ).

Table 2. Results of logistic regression model predicting age classification; β, SE, Wald, df, p , e β , 95% CI ( e β ) of each predictor: all samples.

The further regression models testing the respective groups were significant for developmental familiar samples [χ 2 (4) = 38.62, p < 0.001] and for developmental unfamiliar samples [χ 2 (4) = 50.29, p < 0.001]. For classification of developmental familiar samples, pleasantness, ( p = 0.001), intensity ( p = 0.001), and pubertal status ( p = 0.001) but not hormonal status ( p = 0.706) predicted developmental classification (see Table 3 ). Higher pleasantness related to prepubertal classification, whereas higher intensity and higher pubertal status were associated with postpubertal classification. For classification of developmental unfamiliar samples, only the perceptual ratings, pleasantness ( p < 0.001) and intensity ( p = 0.001), emerged as significant predictors with higher pleasantness predicting pre-, and higher intensity predicting postpubertal classification (see Table 4 and Supplementary Figures 1 , 2 ).

Table 3. Results of logistic regression model predicting age classification; β, SE, Wald, df, p , e β , 95% CI ( e β ) of each predictor: developmental familiar samples.

Table 4. Results of logistic regression model predicting age classification; β, SE, Wald, df, p , e β , 95% CI ( e β ) of each predictor: developmental unfamiliar samples.

The present findings highlight that maternal classification of the body odor changes depending on the pubertal stage of the child. Further, accuracy of maternal classification was moderately low (i.e. around 64%). In detail, we observed a high sensitivity and low specificity in detection of prepubertal status and vice versa – i.e. postpubertal classification corresponded to low sensitivity and a high specificity. Hence, mothers were more prone to identify the presented body odors as prepubertal rather than postpubertal.

Mothers performed better when assessing developmental familiar samples than when assessing developmentally unfamiliar samples. This finding may indicate that mothers being exposed to a certain developmental stage are able to incorporate developmental knowledge better. This is illustrated by analysis of the classification’s determinants – i.e. perceptual evaluation of the body odor, as well as the assessed pubertal status predicted the maternal choice. In particular, the developmental familiar classification was guided by perceptual ratings and developmental information, whereas mothers based their decision on perceptual assessment only when rating developmentally unfamiliar samples.

The overall accuracy of developmental classification was low, although exceeding chance level. Body odors consist of various components including rather stable factors, such as the genetic profile ( Milinski et al., 2013 ), but also highly variable influences, such as food, culture ( Havlíček et al., 2017 ), or disease ( Olsson et al., 2014 ). It is unclear how much variance each of these factors explain in odor perception. Typically, odors are difficult to identify in an unaided identification task and susceptible to label effects ( Cuevas et al., 2009 ; Herz, 2003 ), which explains why odor perception is often ambiguous. Considering those facts, the low odor-identification accuracy found in this study is not surprising. Nonetheless, our data suggest that body odors at least carry the potential to signal developmental stage, which is explained in the following paragraphs.

The maternal susceptibility of detecting prepubertal status suggests that body odors serve as an important signal in human chemical communication. This appears especially true in infancy, when children are dependent on parental care. Parenting in the early childhood is characterized by formation of attachment, enabling the child to survive safely and to develop healthily in the world ( Bowlby, 1958 ). Infantile positive signals, such as a cute baby face or babbling, trigger brain correlates of reward and approach behavior ( Kringelbach et al., 2016 ). This is assumed to apply for body odors as well, and indeed, a baby’s body odor elicits reward on a neural level, especially to mothers ( Lundström et al., 2013 ). In our data, prepubertal status was detectable above chance by all mothers, independent from their expert status, which suggests that an infantile body odor may also serve as a universal cue for cuteness, similar to the “Kindchenschema.” If this effect were to exist, it might have contributed to the maternal tendency to classify a body odor as prepubertal (rather than postpubertal), observed in this study. Further from an evolutionary perspective, our results may reflect a primacy to interpret children’s body odors first as a general “cuteness.” We assume that body odor perception leads to neural and behavioral responses similar to those observed for the “Kindchenschema” – i.e. a set of responses targeted to ensure the child’s survival by formatting a bond that is prioritized over detachment ( Glocker et al., 2009 ). Preliminary fMRI data from our lab indeed indicate that babies’ body odors elicit neural correlates in the maternal brain similar to those reported for facial cuteness ( Schäfer et al., 2019 ). However, further studies investigating the perception of infantile body odors across parents (including fathers) and non-parents still need to clarify the universality of such a stimulus.

Besides cuteness, odors may also communicate a certain degree of maturity. While maternal sensitivity for detecting postpubertal status was lower than for prepubertal status, postpubertal recognition was characterized by a higher specificity. These findings suggest that body odors change with increasing development, – however, which particular features determine this change and drive olfactory perception remains unclear. We did not observe any influence of steroid hormones on age classification. We know from our previous data that steroid hormones can affect maternal evaluation of pleasantness, however this finding is only apparent for male children in the transition from pre-to post-pubertal status [9–13 years ( Schäfer et al., in press )].

We did not observe sex-related differences in maternal classification for postpubertal children. However, an important limitation is that we did not assess the menstrual cycle phase of postpubertal girls, which is known to affect body odor assessment ( Havlíček et al., 2017 ). This should be regarded in further studies.

Salivary steroid hormones were measured in this study. These hormones fluctuate across the day ( Landman et al., 1976 ) and do not always relate to secondary sexual features ( Shirtcliff et al., 2009 ). Nevertheless, it is assumed that steroid hormones indicate maturity in the transition phase when the external development is not yet complete ( Dorn et al., 2006 ). Based on our study we cannot exclude that steroid hormones are perceivable in body odor, further studies using different sampling methods may lead to different effects. Here, the external manifestation of pubertal development affected body odor classification, as children of higher pubertal status were more often classified as postpubertal. Further, this effect was driven by the mothers having experience with postpubertal children. As the onset of puberty is complex and characterized by various endocrinological cascades ( Grumbach, 2002 ), we do not know if hormones other than steroids change body odor composition and further promote postpubertal recognition. The need of chemosensory body odor profiling is hence obvious in order to determine volatile odorants, which constitute body odor and affect hedonic evaluation.

As our study points out, perceptual assessment was a strong predictor for age classification across all mothers. Pleasantness was related to prepubertal classification, which is in line with previous findings on positive evaluation of infant’s body odor ( Fleming et al., 1993 ; Okamoto et al., 2016 ; Croy et al., 2017 , 2019 ). Moreover, pleasantness perception of an infant’s odor is an important cue mediating parental care as it facilitates affectionate love ( Okamoto et al., 2016 ). This affective component of body odor declines with age ( Okamoto et al., 2016 ; Croy et al., 2017 ), which is supported by our results demonstrating that pleasantness drives pre- but not postpubertal classification. The latter was predicted by higher body odor intensity, which has been associated with less positive perception ( Doty et al., 1978 ). In the sense of the mother-child relationship, this leads us to speculate that the intensity drives an avoidant reaction to postpubertal body odors. Hence, this could be interpreted as a mechanism for detachment, when the child becomes more independent and separates itself from parental care ( Beyers et al., 2003 ).

In summary, this study demonstrates that developmental information is transcribed in body odor across childhood. While prepubertal status is generally transmitted and characterized by pleasant perception, postpubertal status is rather detected by mothers having expertise with children in that stage, and accompanied by higher intensity ratings. Mothers are further able to encode developmental information for classification when assessing body odors with similar developmental status to their own child. As the composition of body odor is still poorly understood, it remains to be determined how chemicals manifest body odor and how they actually influence olfactory perception.

Data Availability Statement

The datasets generated for this study are available on request to the corresponding author.

Ethics Statement

The studies involving human participants were reviewed and approved by Ethikkommission TU Dresden. Written informed consent to participate in this study was provided by the participants’ legal guardian/next of kin.

Author Contributions

IC, AS, and LS contributed to the conception and design of the study. LS acquired the data and wrote the first draft of the manuscript. LS and IC performed the statistical analysis. IC wrote the sections of the manuscript. AS and KW critically revised the manuscript. All authors contributed to the manuscript revision, and read and approved the submitted version.

This research was funded by the Deutsche Forschungsgemein-schaft (DFG) for the project (CR479/4-1) “The impact of body odor on bonding and incest avoidance over the course of life: a developmental and neuropsychological approach.”

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Supplementary Material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fpsyg.2020.00320/full#supplementary-material

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Keywords : olfaction, bonding, puberty, chemosignal, body odors, parent–child relationship, age

Citation: Schäfer L, Sorokowska A, Weidner K and Croy I (2020) Children’s Body Odors: Hints to the Development Status. Front. Psychol. 11:320. doi: 10.3389/fpsyg.2020.00320

Received: 02 December 2019; Accepted: 10 February 2020; Published: 04 March 2020.

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Copyright © 2020 Schäfer, Sorokowska, Weidner and Croy. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Laura Schäfer, [email protected]

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The ultimate guide to stopping sweat

Learn why you might be sweating more than normal

8 Ways to Get Rid of Foul Body Odor

• / Author Kellen Purles
• Jan. 4 2022

Table of Contents

Have you ever wondered who’s rocking the eye-watering body odor – only to figure out it’s you? We’ve all been there at some point, whether after a long workout, a big presentation, or just a hot, sticky, humid day. But you don’t have to leave the country in exile, never to be seen again – you can take a few simple steps to prevent and get rid of body odor when it rears its ugly head.

8 Ways to Get Rid of Body Odor

1.  Wear Antiperspirant and Deodorant Daily

2.  Shower with Antibacterial Soap

3.  Freshen Up on the Go with Body Wipes

4.  Control Your Body Hair

5.  Wear Breathable Clothing

6.  Focus on Four Key Odor Zones

7.  Watch Your Diet

8.  Reduce Your Stress

When asked what causes body odor, most people might tell you that it’s your sweat, but that’s only partly true. Keep reading for a few ideas you can try to keep yourself stink-free, even in the sweatiest of situations.

What Causes Body Odor?

Sweat itself doesn’t really have an odor – it’s when the moisture from your odorless sweat mixes with bacteria on your skin that the stink sets in. This added moisture makes a healthy, ideal environment for bacteria to multiply quickly, which leads to a foul odor – and your embarrassment.

Not all sweat is created equally. Some sweat is factory made to stink, while other sweat is mostly harmless on the odor front. So what’s the difference?

Your body has  two types of sweat glands  that produce different kinds of sweat. Sweat caused by exertion or physical activity is chemically different from  sweat caused by anxiety , fear or stress. Stress sweat comes from your apocrine glands; it’s a fatty liquid that bacteria really love.

In contrast, the sweat that’s produced by your eccrine glands is mostly water and salt – these are the glands that are located over most of the surface of our bodies, while apocrine glands are housed in some of our more hairy or private areas – like armpits and groin.

It’s true, though, that not all body odor is directly related to sweat. Some people smell because they have poor hygiene habits, which allows bacteria to thrive on their skin. Others might suffer from a medical condition or take a specific kind of medication that leads to body odor. Certain foods in your diet can also contribute to a bad odor.

Can My Body Odor Change?

The science says yes. For example, rigorous study shows that many women experience body odor changes around the time they start going through menopause. Plus – a drop in estrogen can trigger both night sweats and hot flashes, which just means more sweat and more chance for odor, so the change may be even more noticeable than usual.

In addition, there’s some research that shows we might smell funkier as we get older – there’s an odor-related substance called 2-Nonenal in human sweat that increases as we age. It gives sweat an unpleasant odor – a grassy, greasy smell – and it’s usually detected only in the sweat of those who are ages 40 and above. Great – something to look forward to.

Unfortunately, sometimes there are more sinister reasons behind changes in body odor – diabetes, for example, causes some people’s body odor to have a sweet, fruity smell. If you notice this kind of change in body odor, make sure to talk with your doctor immediately to make sure you aren’t dealing with a serious health condition.

Now, let’s take a closer look at some of the ways you can reduce your stink. You do have options. The following list is a good place to start if you’re wondering how to get rid of body odor.

1. Wear Antiperspirant and Deodorant Daily

Antiperspirants and deodorants can work together to keep you odor-free. While an antiperspirant is formulated to “plug” your sweat glands and stop sweat before it starts, a  good deodorant  can help fight the resulting odor once you do begin to sweat. Make sure you apply your antiperspirant at night so that it has the time while you sleep to fully go to work for you. Consider using a  clinical strength antiperspirant  like SweatBlock, especially if you suffer from an excessive sweating condition known as  hyperhidrosis .

Applying your antiperspirant at night allows the active ingredient to work during a time when your sweat glands are typically the least active. You can use your antiperspirant twice a day if you need it – at night and then again in the morning. It’s a good idea to pair an antiperspirant with a deodorant, which is designed to reduce odor-causing bacteria, but won’t help stop your sweating. When you use them both together, you deliver a one-two punch to body odor.

2. Shower with Antibacterial Soap

It should go without saying that good hygiene, including showering regularly, can help you cut down on body odor. Taking it one step further and showering with an antibacterial soap is even more helpful. Because body odor is directly related to sweat mixing with your skin bacteria, using an antibacterial soap can reduce bacterial growth on your skin in the first place, which also reduces odor. With this move, you’re attacking body odor at its source.

If you’re worried about chemicals in antibacterial products, you can always go for natural products that feature essential oils for body odor – like tea tree oil, peppermint, oregano, and eucalyptus. These products contain bacteria-fighting and odor-fighting qualities that can help keep you smelling fresh.

In general, you should shower at least once a day, maybe more in especially hot weather or after a tough workout. And when you’re finished with your shower, make sure to dry off completely so you don’t leave behind a moist environment for bacteria to quickly repopulate.

3. Freshen Up on the Go with Body Wipes

When you’re on the go and need to freshen up quickly,  body wipes  can be your best friend and ally for fighting body odor. You can simply wipe down your most odor-prone areas to get rid of moisture and bacteria, and many body wipes on the market also offer a fresh, clean scent to replace your funk. They’re convenient and basically give you the same benefit of taking a full shower, without the extra time or trouble. You can keep them stashed in your car, your briefcase, or your desk to use after a lunch workout, before a big meeting or date, and when you’re traveling.

4. Control Your Body Hair

Extra body hair causes trouble in a couple of key ways – it can make you sweat excessively in the first place, and then it can trap moisture and bacteria in a festering pool of odor. If you’ll regularly trim hair – especially under your arms and in your groin area – you’ll rob bacteria of a place to hide and multiply, which will cut down on body odor.

5. Wear Breathable Clothing

Breathable, natural fabrics, including bamboo or cotton, are helpful in both preventing and fighting off sour body odor. Try to look for clothing that helps you minimize excessive sweating in the first place. The right material will pull sweat away from your body so it can evaporate rather than sit on your skin with the chance to mingle with your skin bacteria.

6. Focus on Four Key Odor Zones

While we all certainly sweat all over our bodies, there are four key zones that are the worst offenders when it comes to producing an unpleasant smell:  sweaty armpits ,  feet, scalp, and  sweaty groin . If you’ll focus on those four areas, you’ll help set yourself up for sweet smelling success.

Your groin and your armpits feature the majority of your body’s collection of apocrine sweat glands, which are responsible for your stinkiest sweat. And if you’re not wearing clothes that pull moisture away from your body, underarm sweat has a perfect environment for growing bacteria. It’s moist, with little airflow, and the same is true for your groin area.

While your feet don’t have the same power to get stinky on their own, if you’re wearing shoes and socks all day, you’re creating that same dark, damp, low-air environment that bacteria love – and that means stinky foot odor. But you can help cut down odors by using foot creams or powders – even baking soda – wearing shoes made of natural materials and going barefoot when you can to give your feet a chance to air dry.

You may be surprised that your scalp is listed as a key odor zone, but if you suffer from dandruff, that can also lead to odor as dead skin begins to decompose on your scalp. Yuck. A good dandruff shampoo and mild styling products can help you out here.

7. Watch Your Diet

The foods you eat can often affect your body chemistry and either increase or reduce body odor. Good choices include yogurt, pickles, kefir, fruits, and non-sulfurous vegetables and fresh sauerkraut. And some studies show that eating foods rich in magnesium and zinc like shellfish, pecans, tofu, oysters, and broccoli can be helpful.

On the other hand, spicy foods, processed foods, a high amount of red meat, excess alcohol or caffeine and foods cooked with garlic and onion can make your body raise up the stink factor. Sometimes our favorite spicy foods can crank up our sweat glands – so that alone can increase your chances for foul odor. And the aroma of garlic or onions can literally pass through to your sweat so that you smell like a garlicky, oniony, body odor cloud. Gross.

8. Reduce Your Stress

Because anxiety or fear sweat is generated by the apocrine glands and is often the most likely to cause odor, any way you can manage to reduce your level of stress will be helpful in fighting your body odor. Anxiety and stress activate our sweat glands at full-on survival mode, so relaxation techniques like meditation, biofeedback and yoga, a brisk walk outside or a variety of other calming activities may help get your anxiety – and in turn, your body odor – under control. It might sound impossible, but relaxation activities have historically proven successful for many people.

Get Rid of Body Odor

It stinks to stink. But you’re not alone and you’re not without options. Follow some of the guidelines here to help keep your excessive sweating and body odor under control. You can plan ahead for certain situations and make sure you’re well-armed with what you need to combat body odor – especially when you’re on the go.

If you’re experiencing changes in your sweating or your body odor that are hampering your ability to enjoy your life, check with your doctor to make sure you’re not dealing with a more serious health condition. Otherwise, wash and shower regularly, apply deodorant and antiperspirant, pack your wipes and get ready to smell great.

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Does Human Body Odor Represent a Significant and Rewarding Social Signal to Individuals High in Social Openness?

Katrin t. lübke.

1 Department of Experimental Psychology, University of Düsseldorf, Düsseldorf, Germany

2 Department of Otorhinolaryngology, University of Dresden Medical School, Dresden, Germany

Matthias Hoenen

Johannes gerber.

3 Department of Neuroradiology, University of Dresden Medical School, Dresden, Germany

Bettina M. Pause

Thomas hummel.

Conceived and designed the experiments: KTL BMP TH. Performed the experiments: KTL IC. Analyzed the data: KTL IC. Contributed reagents/materials/analysis tools: JG TH BMP MH. Wrote the paper: KTL.

Across a wide variety of domains, experts differ from novices in their response to stimuli linked to their respective field of expertise. It is currently unknown whether similar patterns can be observed with regard to social expertise. The current study therefore focuses on social openness, a central social skill necessary to initiate social contact. Human body odors were used as social cues, as they inherently signal the presence of another human being. Using functional MRI, hemodynamic brain responses to body odors of women reporting a high (n = 14) or a low (n = 12) level of social openness were compared. Greater activation within the inferior frontal gyrus and the caudate nucleus was observed in high socially open individuals compared to individuals low in social openness. With the inferior frontal gyrus being a crucial part of the human mirror neuron system, and the caudate nucleus being implicated in social reward, it is discussed whether human body odor might constitute more of a significant and rewarding social signal to individuals high in social openness compared to individuals low in social openness process.

Introduction

Across a wide variety of domains, experts differ from novices in their response to stimuli linked to their respective field of expertise. These differences, apparent in overt behavior, are correlated with differential central nervous processing patterns in experts versus novices. For example, when presented with expertise linked stimuli, athletes show stronger activation within task related brain areas compared to novices [1] – [3] . Similar results have been reported when comparing chess masters to chess novices [4] , or professional musicians to musical lay persons [5] . Similar differences between “experts” and “novices” can be expected within the domain of social skills. However, whenever social expertise is reported to affect responses to social stimuli, “normal” control groups are compared to individuals featuring social deficits, such as patients suffering from schizophrenia, or autism spectrum disorders [6] . How social expertise affects brain activation in response to social stimuli when otherwise normal individuals with social skills below average are compared to social experts is currently unknown.

Social expertise, or social competence, can be defined as being able to correctly identify and interpret social and emotional information, being highly sensitive to socio-emotional information, being able to memorize social information, and being able to manage social and emotional situations (for an overview see [7] ). Importantly, in order to establish social contacts, being socially open is a central skill for socially competent people. Following Kanning's model of social skills, “social openness” (German “Offensivität”, [8] ) is characterized by being outgoing and sociable, but also being assertive, decisive, and able to negotiate social conflicts without intentionally causing them. Individuals who describe themselves as high in social openness display a pervasive drive and the necessary skills to initiate and maintain social contact. So far, imaging studies have linked both empathy and social reward sensitivity to brain areas subserving the perception and integration of social information [9] – [11] , as well as the processing of social reward [10] , [11] . Kaplan and Jacoboni [9] interpreted their findings as suggesting a close link between social competence and mirror neuron system activity. Moreover, similar to social openness, social reward sensitivity, as examined in [10] and [11] , reflects the individual disposition to social relationships.

Human body odor represents a ubiquitous and ancient social signal, linked to the domain of social expertise. Humans permanently produce and perceive body odor, and its social and emotional content cannot be manipulated (for reviews on human chemosensory communication see [12] – [15] ). It inherently signals the presence of another individual, and has been shown to carry a diversity of social information, ranging from individual identity [16] , [17] to transiently experienced affect [18] – [20] . Social expertise seemingly affects responses to chemosensory social stimuli, as social anxiety modulates the central nervous processing of human body odors [21] , [22] as well as motor behavior in the context of human body odors [23] . Social anxiety itself is tightly linked to deficits in social skills [24] , causing deficits in social interaction performance [25] , [26] . Emotionally highly competent individuals, on the other hand, presumably also tending to be socially skilled, outperform less emotionally adept individuals in identifying familiar persons by their body odor [27] .

The current study was designed to examine effects of social expertise, precisely social openness, on hemodynamic brain responses to social stimuli, using human body odor as the most basic social stimulus. Comparable to studies in other fields of expertise, an experimental approach comparing highly socially open individuals (“social experts”) with individuals low in social openness (“social novices”) was chosen. Effects of social openness are expected to be most prominent within brain areas involved in social information and reward processing: When presented with human body odor, highly socially open individuals should show stronger hemodynamic responses in these brain regions than individuals low in social openness.

Materials and Methods

Ethics statement.

Participants gave written informed consent and were paid for their participation. The current study, including the sweat sampling procedure, was carried out in accordance with the Declaration of Helsinki and was approved by the University of Dresden Medical Faculty Ethics Review Board.

Participants

Twenty-six right-handed women (mean age: 23.0 years, SD = 2.2, range 18–27) of European descent participated in the current study. Only women were recruited due to their overall greater olfactory abilities compared to men [28] , and especially due to their higher sensitivity regarding chemosensory social cues [21] , [29] , [30] . None of these women reported a history of chronic medication, of neurological, psychiatric, major endocrine or immunological diseases or diseases related to the upper respiratory tract. All participants showed normal olfactory abilities (as tested with the “Sniffin' Sticks” test kit, [31] , [32] ).

In order to identify individuals who would qualify as having a high level of social expertise, and individuals displaying a low level of social expertise, the subscale “Openness” of the “Inventar Sozialer Kompetenzen” (ISK, [8] ), a German inventory for the assessment of social skills was used. Within the ISK short version, which was used within the current study, the subscale “Openness” consists of 8 items, such as “It is quite easy for me to quickly get in with a new group of people.” (German: “Es fällt mir sehr leicht, in einer neuen Gruppe schnell Anschluss zu finden.“), or „I always approach people if I want to get to know them.” (German “Ich gehe immer auf Menschen zu, wenn ich sie kennen lernen möchte.“). Each item is phrased as a statement, and participants are asked to indicate their level of agreement on a scale ranging from 1 ( =  “totally disagree”) to 4 ( =  “totally agree”). Conceptually, social openness is related to extraversion, as well as self-confidence and assertiveness, and socially open individuals have been shown to be attentive towards the behavior of others in social interactions [8] .

In order to recruit participants representing the two experimental groups of “High Level of Openness” (HO; n = 14) and “Low Level of Openness” (LO; n = 12), applicants answered the ISK during individual preparatory meetings. Those participants scoring higher than mean standard score (M = 100) plus one standard deviation (SD = 10; standard score >110) on “Openness” were identified to belong to HO, whereas participants scoring lower than mean minus one standard deviation (standard score <90) were identified to belong to LO. Applicants whose “Openness” scores did not meet these criteria (n = 43) were excluded from participation and thus not invited to the separately scheduled scanning session (see Table 1 for a distribution of “Openness” scores across included and excluded participants). The resulting extreme groups included participants either belonging to the 15.8% highest ranking or to the 15.8% lowest ranking individuals in “Openness” within the population. This approach ensured a high level of statistical power by spanning a wide range of the independent variable, which is especially important in studies with an exploratory character. According to this selection procedure, HO participants (M = 113.86, SD = 3.09) displayed higher “Openness” scores than LO participants [M = 86.33, SD = 3.73; t(24) = 20.62, p<0.001]. HO and LO participants did not differ in age [t(24) = 0.450, p = 0.656].

Chemosensory stimuli

Axillary sweat was sampled from 8 male and 8 female students. These donors were on average 22.5 years old (SD = 2.5, range  = 20–30). Male and female donors did not differ in age [t(14) = 0.39, p = 0.704]. All donors reported being of European origin, and denied any acute or chronic medication. Furthermore, no donor indicated suffering from any neurological, psychiatric, endocrine, or immunological disease, or using drugs. Their body-mass-index ranged from 19.3 to 26.0 kg/m 2 (M = 22.5, SD = 1.9), and all of them were non-smokers. Female donors reported having a regular menstrual cycle and denied use of hormonal contraception.

The donors were instructed to refrain from eating garlic, onions, asparagus, or any other spicy or aromatic food during the 24 hours prior to the odor donation. They were further advised to refrain from using deodorants within this timeframe, and to wash their armpits exclusively with an odorless medical soap (Eubos, Dr. Holbein GmbH, Germany). Male as well as female donors shaved their armpits one day prior to the odor donation. For collecting the axillary odors, one cotton pad was fixed in each of the donor's armpits. The axillary odors were sampled during sleep over the course of one night (sampling duration: M = 8.5 h, SD = 1.0 h). All donors gave written informed consent and were paid for their donation. None of the odor donors acted as a participant within the current study.

Following the completion of collection, cotton pads carrying the sweat samples were chopped and pooled with respect to the donor's sex, then divided into small portions of 0.6 g cotton pad and stored at −20°C. Additionally, samples of pure, unused cotton pads were treated the exact same way to provide for baseline measurements within the fMRI sessions.

Stimulus Presentation

Participants underwent four scanning sessions in total. In two of these sessions they were presented with male body odors, while in the other two they were presented with female body odors. The order of the scanning sessions was counterbalanced across groups. A self-constructed olfactometer delivered odor pulses embedded in a constant flow of humidified, odorless air in order to avoid any mechanical stimulation. The odors were presented birhinally and intranasally (inner diameter of the Teflon tubing: 4 mm), with a total airflow of 2 liter per minute. Further, the odors were delivered non-synchronously to breathing, as participants performed the velopharyngeal closure technique [33] . The body odors (during ON blocks) as well as the odor-free, pure cotton pads (during OFF blocks) were presented for a period of 1 second with an interstimulus interval of 2 seconds (see Fig. 1 ).

The participants underwent 4 scanning sessions in succession. Each session consisted of 6 ON-blocks (with presentation of body odor) and 6 OFF-blocks (with presentation of odor-free, pure cotton pad), resulting in a total of 12 blocks. During each block, the stimuli were presented for a period of 1 s with an interstimulus interval of 2 s. Each block had a duration of 22 s, during which 8 scans were conducted.

Participants were not cued for stimulus presentation, and were not asked to perform any detection or other cognitive tasks. Following each session, however, participants were asked to rate the odor's intensity (0 =  not perceivable; 10 =  extremely intense) and hedonic quality (−5 =  extremely unpleasant; 5 =  extremely pleasant).

fMRI Protocol

A 1.5 T scanner (SONATA-MR, Siemens, Erlangen, Germany) was used for fMRI data acquisition. For functional data 96 volumes per session were acquired by means of a 33 axial-slice matrix 2D SE/EP sequence. Scan parameters included a 192×192 mm 2 field of view, a TR of 2500 ms, a TE of 40 ms, a 64×64 matrix, a 90° flip angle, a slice thickness of 3 mm, and a voxel size of 3×3×3.75 mm 3 . Additionally, T1-weighted images were acquired using a 3D IR/GR sequence (TR: 2180 ms/TE: 3.39 ms) to localize activated areas. Eight dummy scans were conducted at the beginning of each session to allow the magnetization to reach magnetic equilibrium. Utilizing a block design, in each session the participants received 8 scans during the 22 s ON blocks and 8 scans during the 22 s OFF blocks (see Fig. 1 ). ON and OFF blocks were repeated 6 times in alternation. Each session lasted 4∶40 minutes.

fMRI Data Analysis

Preprocessing and statistical analysis were performed using the statistical parametric mapping software package (SPM8, Wellcome Trust Centre for Neuroimaging, London; www.fil.ion.ucl.ac.uk/spm ) implemented in Matlab R2010b (Math Works Inc., Natick, MA; USA). Head motions across time were corrected by realigning all scans to the first volume. Participants' T1-weighted images were co-registered to the corresponding mean EPI images and subsequently normalized to Montreal Neurological Institute (MNI) standard space using the segmentation procedure. EPI images were then normalized using the parameters written during segmentation of co-registered T1-weighted images and spatially smoothed using an isotropic Gaussian kernel at 6 mm full width at half maximum.

The responses to male and female body odors were combined for analyses, as the current literature does not provide data that would allow for specific sex-related hypotheses. Both body odors were presented during scanning in order to prevent any bias that might result from processing of same-sex vs. other-sex body odors. However, the odors were not combined during scanning to avoid creating an artificial chemosignal.

In order to identify the effects of the body odor presentation, first level linear contrast images were entered into a general linear model, applying a canonical hemodynamic response function. Statistical parametrical maps were generated for each participant. The parameters written during realignment were entered as multiple regressors to capture residual movement artifacts. A high-pass filter of 128 ms was applied in order to exclude variance due to aliasing. In order to examine the effects of the level of social openness, the resulting contrast images were analyzed using a two-sample-t-test.

Further, in order to test whether the presentation of body odors in general activated brain areas reported to be involved in the processing of complex social chemosignals (for reviews see [12] , [14] ), a second level analysis across all participants, using a one sample t-test, was performed. These networks include the fusiform cortex [19] , [34] , the anterior and posterior cingulate cortex [19] , [35] , [36] , and the insular cortex [19] , [36] . Accordingly, a Region of Interest Analysis was performed for those regions. Masks were created using the WFU Pick Atlas 3.0.3 [37] , [38] toolbox for SPM. The statistical threshold was set at p<0.001 (uncorrected), and the minimum cluster size was set at k = 20. The coordinates of the activation are presented according to MNI.

The hemodynamic brain response to the body odors presented indeed varied with social openness. Comparing the parameter estimates of the first level ON-OFF-contrasts in HO versus LO participants showed greater activation within the right inferior frontal gyrus (peak located at x = 40/y = 38/z = 0; t = 5.26; cluster size 37, see Fig. 2 ), and within the right caudate nucleus (peak located at x = 16/y = 22/z = 14; t = 4.28; cluster size 33, see Fig. 2 ) in HO compared to LO participants. The reverse (LO vs. HO) contrast did not yield any suprathreshold activation. Further, significant linear relationships between individual beta values and social openness scores were observed: Social openness scores were highly positively correlated with both peak activation within the right inferior frontal gyrus (r = 0.715, p<0.001, see Fig. 3 , left paragraph) and the right caudate nucleus (r = 0.685, p<0.001, see Fig. 3 , right paragraph).

HO participants show activation within the right inferior frontal cortex and within the right caudate nucleus (k≥20; p<0.001). For visualization a normalized template provided by SPM 8 software (single_subj_T1.nii) was used.

Left paragraph: Peak activation within the inferior frontal gyrus vs. social openness scores; right paragraph: Peak activation within the caudate nucleus vs. social openness scores.

Contrasting the perception of body odors (ON) with the perception of pure cotton pad (OFF) across all participants, using the specified masks, significant activation within the fusiform cortex, the anterior and posterior cingulate cortex and the insular cortex was evident (see Table 2 , Fig. 4 ). The reverse contrast did not yield any suprathreshold activation.

Parameters: k≥20; p<0.001; contrast: ON vs. OFF. For visualization a normalized template provided by SPM 8 software (single_subj_T1.nii) was used.

In general, the participants judged the body odors as being relatively weak (M = 2.85, SD = 1.31), and almost neutral in quality (M = 0.68, SD = 1.08). The level of social openness did not affect these ratings (ps>0.10). However, both intensity (r = 0.352, p = 0.046, one-sided test) and, by trend, pleasantness ratings (r = 0.300, p = 0.078, one-sided test) were related to the hemodynamic response within the caudate nucleus, with higher peak activation corresponding to judging the body odors as more intense, and more pleasant, respectively. The correlational analyses are based on n = 24 individuals after excluding n = 2 individuals scoring higher than mean plus two standard deviations on the valence ratings. Including these individuals results in correlations of r = 0.399 (p = 0.022, caudate vs. valence ratings) and r = 0.198 (p = 0.166, caudate vs. intensity ratings), respectively.

This study aimed to compare brain responses to human chemosensory social signals of individuals describing themselves as high in social openness (HO) with the brain responses of individuals describing themselves as low in social openness (LO). Consistent with the hypotheses, HO participants display stronger activation than LO participants in brain regions known to be involved in social perception (inferior frontal gyrus) and within the reward system (caudate nucleus). These results suggest that HO individuals perceive human body odors as subjectively important social signals associated with positive experience more readily than LO individuals. This effect, however, seems not to extend to conscious evaluation, as HO and LO individuals do not differ in their judgments of the body odors' qualitative features.

The inferior frontal gyrus has been shown to be involved in social perception, as it is activated when viewing (emotional) faces (for a review see [39] , [40] ), during implicit facial judgments [41] or when observing positive and negative social encounters [42] . Moreover, activity within the inferior frontal gyrus is found to be positively correlated with the level of trait empathy [43] , and individuals with an empathizing rather than systemizing cognitive style show pronounced activity within the inferior frontal gyrus during a face-based mind reading task [44] . Empathy seems to be crucial for social interaction. It can be regarded as having a concept about how another individual feels, being able to take another one's perspective and, in some instances, displaying a corresponding response [45] . Hence, the concept of empathy is closely related to social openness and other social competencies. In general, the inferior frontal gyrus is discussed as a crucial part of the human mirror neuron system [46] , [47] . Accordingly, in HO individuals compared to LO individuals, body odors more readily activate components of a system thought to mediate the perception and recognition of actions and emotions, which is pivotal for social cognitive functioning.

The current study is the first to report activation within the reward system in response to human chemosensory social signals (for a recent meta-analysis of basal ganglia functions see [48] ). HO compared to LO individuals display a stronger hemodynamic response to body odors within the caudate nucleus. Both activation within the ventral striatum (nucleus accumbens) and the dorsal striatum (caudate nucleus, putamen) have been reported consistently in positive social interaction, indicating that reward processing and social interaction share common neural substrates [49] , [50] . It has even been demonstrated that the individual disposition to social openness is positively associated with the gray matter density within the striatum [10] . Considering social perception and behavior, the caudate nucleus is discussed as a neuronal correlate of trust [51] , [52] and thus to be implemented in a neuronal network that positively reinforces reciprocal altruism and cooperation [53] , [54] . Moreover, it has been shown to be involved in the anticipation of positive (social) encounters in the near future [55] . Interestingly, recent research showed that socially isolated individuals show less activity within the reward system in response to people than to objects, while non-lonely individuals show the opposite response pattern [56] . The authors concluded that socially isolated individuals are less rewarded by social stimuli than non-lonely individuals, mirroring the results of the current study. Here, the social signal of human body odor seems more rewarding to individuals high in social openness, than to individuals low in social openness.

Both neural responses within the inferior frontal gyrus, and neural responses within the caudate nucleus increase in strength with rising social openness scores. These results suggest that the differences between HO and LO individuals might be driven by a linear relationship between social expertise and brain responses to social odors. However, the design underlying the current study applied a two-group approach, comparing participants either belonging to the 15.8% highest ranking or to the 15.8% lowest ranking individuals in social openness within the population. Individuals showing intermediate levels of social expertise were excluded from participation, similar to other studies comparing “experts” and “novices” (e.g. [1] , [2] , [4] , [5] ) While promising, conclusions based on the results of the correlational analyses appear somewhat limited due to “missing data” within the medium range of social expertise. The issue of a potential linear relationship between social expertise and brain responses to social odors thus needs to be addressed within upcoming research.

Across all participants, the presentation of body odors activated the fusiform cortex, the cingulate cortex, and the insular cortex. These areas are discussed as being part of specialized neuronal networks involved in the processing of chemosensory social signals, strongly overlapping with areas implicated in the processing of other socioemotional information [12] , [14] . The pattern of activation observed within the current study strongly suggests that the utilized body odors were processed as social signals.

The statistical criterion for significant contrasts was set at a rather liberal level (p<0.001, uncorrected) within the current study. While this threshold is not uncommon in olfactory fMRI [57] – [59] , it was basically intended to account for the exploratory nature of this study. Still, the minimum cluster size was set at a comparably conservative level of k = 20 in order to detect meaningful hemodynamic responses. Future studies with higher statistical power resulting from larger sample sizes will allow for being statistically more conservative.

The body odors were judged as relatively weak and almost neutral in quality. Several other studies have shown similar patterns of weak and even non-detectable body odors [19] , [21] , [60] . However, similar to the current study, these body odors reliably elicited differential central nervous processing patterns despite their weak intensity. Moreover, despite the relatively weak intensity and neutral quality, analyses revealed a positive linear relationship between peak activation within the caudate nucleus and pleasantness as well as, by trend, intensity ratings. Individuals perceiving the body odors as relatively more intense and pleasant also showed a stronger hemodynamic response within the reward system. This relationship strongly suggests that the current results indeed derive from the presentation of the body odors, and are not mainly driven by some general difference between HO and LO individuals in their response to external stimulation.

Taken together, the current results suggest that high compared to low socially open individuals tend to process human body odors as significant and valued social signals. In general, individuals describing themselves as outgoing, as having a positive attitude towards others, and as being able to show appropriate behavior in social situations, experience social interaction as considerably more rewarding than individuals describing themselves as shy, less socially competent and more socially anxious. As human body odor inherently indicates the presence of others, for individuals high in social openness it might signal the opportunity to engage in putatively appreciated social interaction. The current study, however, does not allow for concluding that this pattern is restricted to the perception of chemosensory social signals. Future research might show in how far similar effects of social expertise are observable in response to other kinds of social stimuli, such as faces or voices. Moreover, future research should examine how such differences between “social experts” and “social novices” directly affect social behavior.

Acknowledgments

The authors would like to thank Friederike Barthels for her help in collecting the body odor samples, and Sabine Schlösser for helping during language editing.

Funding Statement

The authors have no support or funding to report.

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Peer-reviewed

Research Article

The Smell of Age: Perception and Discrimination of Body Odors of Different Ages

Affiliations Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America, Swarthmore College, Swarthmore, Pennsylvania, United States of America

Affiliations Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America, Section of Psychology, Dept. Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden

Affiliation Section of Psychology, Dept. Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden

* E-mail: [email protected]

Affiliations Monell Chemical Senses Center, Philadelphia, Pennsylvania, United States of America, Section of Psychology, Dept. Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden, Department of Psychology, University of Pennsylvania, Pennsylvania, United States of America

• Susanna Mitro, 
• Amy R. Gordon, 
• Mats J. Olsson, 
• Johan N. Lundström

• Published: May 30, 2012
• https://doi.org/10.1371/journal.pone.0038110
• Reader Comments

Our natural body odor goes through several stages of age-dependent changes in chemical composition as we grow older. Similar changes have been reported for several animal species and are thought to facilitate age discrimination of an individual based on body odors, alone. We sought to determine whether humans are able to discriminate between body odor of humans of different ages. Body odors were sampled from three distinct age groups: Young (20–30 years old), Middle-age (45–55), and Old-age (75–95) individuals. Perceptual ratings and age discrimination performance were assessed in 41 young participants. There were significant differences in ratings of both intensity and pleasantness, where body odors from the Old-age group were rated as less intense and less unpleasant than body odors originating from Young and Middle-age donors. Participants were able to discriminate between age categories, with body odor from Old-age donors mediating the effect also after removing variance explained by intensity differences. Similarly, participants were able to correctly assign age labels to body odors originating from Old-age donors but not to body odors originating from other age groups. This experiment suggests that, akin to other animals, humans are able to discriminate age based on body odor alone and that this effect is mediated mainly by body odors emitted by individuals of old age.

Citation: Mitro S, Gordon AR, Olsson MJ, Lundström JN (2012) The Smell of Age: Perception and Discrimination of Body Odors of Different Ages. PLoS ONE 7(5): e38110. https://doi.org/10.1371/journal.pone.0038110

Editor: Thomas Hummel, Technical University of Dresden Medical School, Germany

Received: December 22, 2011; Accepted: May 3, 2012; Published: May 30, 2012

Copyright: © 2012 Mitro et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This work was supported in part by the National Institute on Deafness and other Communication Disorders – NIDCD (R03DC009869) [ http://www.nidcd.nih.gov ] and the Swedish Research Council – VR (2008-20712)[ http://www.vr.se/inenglish.4.12fff4451215cbd83e4800015152.html ]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding received for this study.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Body odor’s chemical complexity [1] enables it to convey a plethora of biological and social information. In human and non-human animals alike, signals hidden within the body odor cocktail have been suggested to aid in mate selection [2] , [3] , [4] , [5] , individual recognition [6] , [7] , [8] , [9] , kin detection [2] , [10] , [11] , [12] , [13] , [14] , [15] , and sex-differentiation [16] , [17] , to name a few [18] .

There is mounting evidence that body odors also carry age-related information and that animals are able to accurately detect and process that information. It has long been known that the chemical composition of body odors changes in an age-dependent manner in a variety of non-human animals, such as mouse [19] , [20] , [21] , black-tailed deer [22] , rabbit [23] , otter [24] , and owl monkey [25] .

However, some of these studies compared very young and adult animals, leaving the unexplored possibility that the demonstrated findings were mediated by a difference in diet; for example, the young animals may still have been nurtured entirely or partly by breast feeding. Indeed, diet is known to affect the chemistry and perception of body odors [26] . In addition, none of these studies demonstrated an ability to differentiate between body odors of different-aged conspecifics. In contrast, Osada and colleagues [20] demonstrated that mice can discriminate between adult and old-age conspecifics based on body odor alone and that this effect was mediated by differences in the quality, rather than the intensity, of the body odors. Together, this evidence suggests that several non-human animal species have the ability to process the age-dependent signals in body odor, and a few studies have even demonstrated that human participants are able to discriminate between animals of different ages based on their body odors alone [23] , [24] . Nevertheless, whether humans, like mice, have the ability to infer the age of conspecifics based on body odors alone remains unanswered.

Reported personal observations indicate that human body odors change throughout the life cycle. It is commonly said that old-age individuals have a characteristic body odor, the so-called “nursing home smell” or “old people smell,” an observation that seems to be culture-independent. In humans, dermal body odors originate from a complex interaction between skin gland (eccrine, sebaceous, apocrine) secretions and bacterial activity [27] , and skin gland composition and secretion change in an age-dependent manner throughout development. The sebaceous gland is found over much of the skin’s surface and secretes a complex mixture of lipids (sebum) and fatty acids [28] , both important precursors to human dermal body odor [29] . In contrast to the eccrine gland (the so-called ‘sweat gland’), the sebaceous gland is less active in young age, reaches peak activity in adulthood, and sharply returns to low activity in the mid-to-late portion of the seventh decade of life [30] . The apocrine glands demonstrate a similar, age-dependent functionality [28] . As a direct reflection of the sebaceous gland’s activity, the skin’s fatty acid composition and variation demonstrate a large degree of similarity between young and very old individuals [31] . To date, two chemically-related compounds have been confirmed to vary with age in humans: nonenal [32] and nonanal [33] . Both compounds increase with age, particularly older individuals, who exhibit a sharp increase in concentration. Thus, taken together, the age-dependent glandular changes and resulting secretory changes, as well as changes in individual chemical components of the dermal body odor mixture, suggest that the needed chemical precursors for behavioral discrimination between age groups based on body odors exists in humans.

Based on the clear evidence from the non-human animal literature and the demonstrated age-dependent differences in human body odor chemistry, we assessed whether humans are able to extract and process age-dependent signals in body odors sampled from conspecifics. To this end, we collected body odors from donors representing three distinctly separate age categories: Young (20–30 years); Middle-age (45–55 years); and Old-age (75–95 years) adults. Young research participants then attempted to discriminate between age categories in a side-by-side comparison, to group them according to age, as well as rate their perceptual properties. We tested two specific hypotheses using forced-choice discrimination and a labeled group test: individuals (1) can discriminate between body odors based on age of the donors and (2) can correctly assign an age group label to body odors.

Perceptual Ratings

To limit the possibility that potential age-dependent signals would be obfuscated by unknown, individual-specific signals, we created so-called supra-donor stimuli comprised of body odors from multiple individuals of the same age category (see Materials and Methods for a detailed description). Participants initially rated each body odor stimulus’ perceived pleasantness using visual analog scales [34] , and intensity using labeled magnitude scale [35] , where high values indicate pleasant and intense, respectively. There was a significant difference in perceived intensity between body odors of the three age groups, F (2,76) = 31.32, p <.01, with subsequent posthoc tests demonstrating that all three possible comparisons demonstrated significant differences (see Table1 for mean values). As seen in Figure 1A , body odors from the Old-age (O) group were rated as significantly less intense than body odors from both the Middle-age (M; p <.01) and the Young (Y; p <.03) groups. Body odors from the M donors were rated as more intense than body odors originating from the Y donors ( p <.01). There was no main effect of participant sex on intensity ratings, F (1,38) = .47, p  = .49; however, there was a significant effect of donor sex, F (1,38) = 28.64, p <.01 as well as a significant interaction between donor sex and donor age group, F (2,76) = 45.64, p <.01. Subsequent Bonferroni posthoc tests demonstrated that M males were rated as most intense and O males least intense (Y vs. M: p <.01; M vs. O: p <.01; Y vs. O: p <.01). There were no significant interactions between donor age group and donor sex, F (2,76) = 2.15, p  = .12, or between donor sex and participant sex, F (1,38) = .26, p  = .61, with respect to the ratings of perceived body odor intensity.

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A ) Mean intensity ratings for each body odor category divided by sex of body odor donor. B ) Mean pleasantness ratings for each body odor category divided by sex of the body odor donor. Negative values indicate ratings on the unpleasant spectra whereas positive values indicate ratings on the positive spectra. C ) Mean discrimination performance, measured in percentage correct responses, according to comparison and donor sex. Solid line in graph represents chance performance (50%). D ) Left hand side indicates total correct pairings of each body odor category and right hand side indicates mean correct age labeling of the body odors. In all graphs, error bars denote standard error of the mean (SEM).

https://doi.org/10.1371/journal.pone.0038110.g001

https://doi.org/10.1371/journal.pone.0038110.t001

Although our method of using supra-donor stimuli, in comparison to the method of using stimuli from individual body odor donors, greatly reduces the possibility that body odor of a single donor would mediate the demonstrated effects, one could postulate that the odors of one or two individuals mediated the effects by a potential outlier effect. To ascertain that our effects were not mediated by potential outliers within our supra-donor stimuli, we performed two additional analyses. First, we plotted intensity ratings for each odor category by the participant testing order and smoothed the intensity ratings with a five-subject wide full width at half maximum Gaussian smoothing kernel. The smoothing kernel corresponded to the number of participants for whom an individual odor quadrant was used and was applied to remove individual differences in intensity ratings since these would obscure potential trends in the data. The rationale behind this analysis is that - because odor quadrants were used more or less in the order they were acquired - if one or more odor donors were mediating the demonstrated differences in intensity ratings, there would be a marked difference in ratings when that donor was included in a supra-donor stimulus. As can be seen in Figure S1 , there is only one “bump” in the intensity ratings (young males, around testing order positions 29–34). Because supra-donor stimuli were changed after every five subjects, this is the only visually identifiable deviation from the norm. Nevertheless, to investigate this visual effect further, we performed a subsequent outlier analysis of mean intensity ratings using a generalized ESD test for outliers (testing for up to 10 outliers) [36] . This analysis demonstrated that no single supra-donor stimulus could be identified as a statistical outlier (all λs, ns).

The results for the pleasantness ratings were very similar to those from the intensity ratings. There was a significant difference in perceived pleasantness between body odors of the three age categories, F (2,76) = 18.16, p <.01. Subsequent posthoc tests demonstrated that body odors from O donors were rated as significantly less unpleasant than body odors originating from both M donors ( p <.01) and Y donors ( p <.01; see Figure 1B ). Body odors from M donors were, however, not perceived as significantly different in pleasantness from Y donors ( p  = .26). As with the intensity ratings, there was no significant main difference in how participating women and men rated the body odors, F (1,38) = 1.08, p  = .31, but there was a significant effect of donor sex, F (1,38) = 78.15, p <.01, and a significant interaction between donor sex and donor age group, F (2,76) = 42.90, p <.01. All age groups of male body odor stimuli differed significantly in pleasantness from one another, with M male odor always rated most unpleasant and O male odor most pleasant (Y/M, p <.01; M/O, p <.01; Y/O, p <.01). Among the female body odors, M female odor was rated significantly more pleasant than O female odor ( p  = .01). No other female body odors differed significantly in pleasantness (Y/M, p  = .08; Y/O, p  = .75). There were no significant interactions between donor age group and participant sex, F (2,76) = .19, p  = .82, or between donor sex and participant sex, F (1,38) = .65, p  = .42, with respect to the ratings of perceived body odor pleasantness.

Age Discrimination Task

We assessed ability to discriminate between age groups with a two-alternative, forced-choice test repeated nine times for each age category with the task of determining which one of the two stimuli originated from the older donor. Participants were able to discriminate between body odors of different age categories, as demonstrated by the significant overall main effect of donor age group, F (1,64) = 4.54, p <.02 (see Table 1 for mean values). There was no main effect of donor sex, F (1,32) = .73, p  = .39, or participant sex, F (1,32) = .86, p  = .36, on participants’ ability to discriminate between the age categories of body odors. However, there was a significant interaction between the factors of donor age group and donor sex, F (1.39,32) = 5.29, p <.02, indicating that – as with the perceptual ratings – participants’ ability to extract age-dependent information from body odors depends on the sex of the odor donor. There was no significant interaction between donor age and participant sex, F (1.71,64) = 1.88, p  = .16, as well as between donor sex and participant sex, F (1,23) = .01, p  = .91.

Subsequent one-sample Student’s t -tests against expected chance performance (50%) demonstrated that participants were significantly able to discriminate M female odors from O female odors ( p <.04) and Y male odors from O male odors ( p  = .05). However, these significant values did not survive subsequent Bonferroni corrections of the alpha value to adjust for repeated statistical testing. No other comparisons reached significance ( Figure 1C ).

Age Labeling Task

When asked to label each body odor according to the three age categories, participants were not able to correctly label either the Y body odors (mean correct.63 out of a total 2) or the M body odors (mean correct.65 out of a total 2), according to χ 2 contingency tests (both p >.10). However, O body odors were correctly labeled (mean correct.74 out of a total 2) significantly more often than expected, according to the χ 2 contingency tests, χ 2 (2, 36) = 14.10, p <.01; Figure 1D ). No sex-dependent differences were observed for this task.

Implicit Age Categorization Task

Neither Y (mean correct 7) nor M (mean correct 6) body odor stimuli were correctly grouped together more frequently than chance (Y: p  = .92; M: p  = .96; Figure 1D ). However, O stimuli (mean correct 18) were correctly grouped together significantly more frequently than chance ( p <.01).

This experiment suggests that, akin to other animals, humans are able to discriminate age based on body odor, alone, and that this effect is mediated mainly by body odors emitted by individuals of old age. The mechanism behind this effect is not currently known, even in non-human animals [20] . Few studies have explored age-related changes in body odor composition, and those few studies have included only a restricted number of participants of the advanced age studied in the experiment [32] , [33] . Nevertheless, these studies suggest that elevated levels of certain chemicals are a potential biomarker for old age.

The results of this study support the cross-culturally popular concept of an “old person odor.” Participants were able to discriminate between age groups as well as group the Old-age body odors together significantly more often than expected by chance. Interestingly, the demonstrated ability to discriminate among age groups was mediated entirely by discrimination of the body odors originating from Old-age donors. The age discrimination ability was not, however, a straightforward effect; instead, the interaction between donor age group and donor sex indicated a complicated relationship. It has been demonstrated that many animal species are very good at determining the sex of a conspecific based on body odor alone [37] . Whether humans also have this ability is still under debate. Although several studies have demonstrated that humans indeed have the capacity to accurately determine sex based on body odors sampled from axillary regions [38] , [39] , [40] , palm odors [41] , and oral odors [42] , assignment of sex seems to be dependent on the perceived intensity and pleasantness of those odors, specifically, intense and unpleasant odors tend to be assigned to the male category [38] , [42] . In the present study, there were significant differences in perceptual ratings of body odors originating from male and female donors for all age categories except the Old-age group. These perceptual differences clearly demonstrate that body odors have age-dependent odor characteristics. In addition, participants were able to discriminate between age categories at a higher-than-chance frequency even after variances explained by intensity differences were removed.

The lack of a significant difference in perceived intensity and perceived pleasantness between the body odors of Old-age men and women parallels previous studies. The concentration of lipids present on the skin surface begins to decline to pre-pubescent levels with older age, returning to childhood levels around age 80 [31] , suggesting that older men and women share skin chemistry features important for body odor production that are not uniform between the sexes at younger stages of maturity. Moreover, Gallagher and colleagues [33] recently demonstrated that there are no clear differences in whole-body odor composition between elderly men and women. Our finding that body odors originating from Old-age men and women were grouped together in the Implicit Age Categorization task supports these data and suggests that any potential perceptual differences were subservient to the potential age-dependent information.

The body odors donated by the older participants were rated as having a neutral valence. In light of the reports in the popular press where the so-called old age odors are commonly described as unpleasant, this outcome was not predicted. What mediates this discrepancy is not known. However, in everyday life, the old age odor is experienced in the context of an old individual being present. Odor valence ratings are highly dependent in which on the context they are experienced. A recent study demonstrated that the label assigned to an odor is a very important predictor of the rated pleasantness in that a label can turn an unlabeled neutral odor into an odor perceived as very negative [43] . Thus, it is likely that the body odors originating from the old individuals would have been rated as more negative if participants were aware of their true origin.

The ecological relevance of body odor-dependent age discrimination can only be speculated about at this stage. In the non-human animal literature, the ‘good genes’ model [44] has been put forth as an explanation for why female animals are attracted to the odors of older males [20] or why female insects prefer the sex pheromone from older male insects [45] . Signals indicating old age, supposedly regulated by the immune system [2] , are favored due to the likelihood that individuals who reach old age possess a strong and adaptive immune system, as well as other adaptive advantages that have allowed them to grow older than their peers. Indeed, older male insects have a higher reproductive success than their younger competitors [44] , [45] . According to the standard evolutionary model, reproductive success is a highly sought-after trait. If indeed the age-dependent signals are regulated by the immune system, attempts to dishonestly and prematurely display ‘old age odor signals’ to enhance reproductive success would be associated with a reduction in immune function; this is an elegant means to ensure signal honesty. However, regardless of the biological mechanism regulating these signals, their potential impact in modern human society is likely very limited given the high social value given to visual attributes of age. Although participants were statistically able to discriminate between body odors, as well as able to group them correctly in an age-dependent manner, we want to point out that the nominal effects are modest and participants expressed a low degree of confidence in their abilities.

Studies attempting to assess behavioral relevance of chemical signals in humans using off-site sampling of stimuli, such as the present one, are conceivably affected by numerous factors outside the control of the experimenter. The balance between ecological relevance and stimuli purity is a balance between diametrical aims. Ecological relevance would be maximized when no environmental and behavioral restrictions are enforced upon the body odor donors but relevant signals might be masked by environmental and hygiene odors. Stimulus purity would be maximized if collection took place over weeks in a laboratory environment but donor recruitment and retention would be cumbersome. Although considerable efforts were made to control the collection of body odors within a donor’s home (including detailed t-shirt handling instructions, dietary restrictions, personal hygiene regulations, etc.), differences in lifestyle, living environment, and other factors outside our control might still contribute to the demonstrated age discrimination. We believe, however, that the impact of these variables is minor and counteracted by the use of supra-donors, which minimize any non-age-dependent factors not presented in a majority of the donors. Similarly, due to the scarcity of Old-age body odor donors who were not using regulated pharmaceutical compounds, some individuals in the Old-age donor group did use regular medication. Although none of the medications are known to affect body odor composition, and although there was no difference in perceptual ratings of body odors from individuals using medication and those not using medication, it is still conceivable that this age-dependent discrimination, driven by the Old-age odors, is to some extent mediated by the metabolites of pharmaceutical compounds secreted into the body odors sampled from those elderly donors.

Being the very first study to assess the ability of human participants to determine age from body odors, we focused on a very narrow research question and much remains to be explored. Only young experimental participants were included in this study. It is very much conceivable that the effects demonstrated in this study displays a double age-dependent effect, i.e. that age of the rater has an impact on the ability to determine the age of the body odor donor. Moreover, great care was taken to avoid contamination of exogenous odors, thus lowering the ecological validity of the study. Of interest would be to explore what impact natural masking with hygiene product would have on the demonstrated results.

We can at this point only speculate as to what the potential biological mechanisms could be. It is has been speculated that polymorphonuclear leukocytes [46] , a type of white blood cells that demonstrate an age-dependent increase in humans, might be a potential biomarker worth exploring in future studies. Previous studies exploring potential biomarkers of age in human and animal body odors have not been conclusive and often fail to take very old age individuals into account. Nevertheless, identifying potential biomarkers is of great interest and would assist in isolating the underlying biological mechanisms mediating and developing these effects.

In conclusion, these data suggest that, akin to other animals, humans are able to discriminate old individuals from younger individuals based on body odor. The modest effects suggest a limited impact on our everyday interactions but does support previous reports of a unique ‘old person odor’. Further experimental work is clearly warranted to determine the mechanism and function of body odor-dependent age discrimination.

Materials and Methods

Ethics statement.

All participants provided written, informed consent prior to participation, and all aspects of the study were approved by the University of Pennsylvania’s Institutional Review Board (IRB) prior to starting the study and performed in accord with the Declaration of Helsinki on Biomedical Studies Involving Human Subjects.

Participants

A total of 41 healthy participants [21 women; mean age 25.0 years (SD 2.7 years); age range 20–30 years] were included in the final analyses, after the exclusion of four individuals (3 women) characterized as hyposmic based on the clinical norms of the olfactory identification test [47] . No participant donated body odor to the study. The following criteria excluded participation: activly smoking, taking psychopharmacological substances, taking systemic medication (including any hormonal contraceptives), having experienced a head trauma leading to unconsciousness, or self-identifying as anything other than strictly heterosexual. The last restriction was implemented due to previously-demonstrated sexual preference-dependent ratings of body odors [48] . All participants provided written, informed consent prior to participation, and all aspects of the study were approved by the University of Pennsylvania’s IRB.

All included women but five were tested in the follicular phase of their menstrual cycle (day 8–15). Of these five women, three were tested in their menstrual phase (day 1–7) and two in their luteal phase. Dates were defined by post menses onset based on self-report [49] .

Body Odor Donors and Odor Collection

Body odors were sampled from individuals in one of three age groups, ‘Young’ (Y, 20–30y), ‘Middle-age’ (M, 45–55y), or ‘Old-age’ (O, 75–95y). A total of 41 healthy donors, adhering to the same exclusion criteria as the experimental participants, were used. Sixteen individuals (8 women) donated body odor to the Young and Middle-age groups, and 12 individuals (6 women) donated to the ‘Old-age’ group. Donors in the ‘Old-age’ group were permitted to use medication for ailments such as hypertension, cholesterol, and acid reflux, because we were unable to locate a sufficient number of Old-age donors who were not using any compounds classified as FDA-regulated drugs. There are, however, no known reports that these medications alter body odor perception or composition. Donors were selected such that the entire age range of each age group was evenly covered. The samples provided by one Young man, one Middle-age man, and one Old-age man were excluded for smelling of soap or for having a body odor undetectable to the experimenter, which brings those individuals' compliance with the sampling procedures into question. All donors provided written, informed consent prior to participating in the study.

Body odors were collected from donors’ armpits using nursing pads (Ultra-Thin Nursing Pads, Gerber Inc., ON, Canada) sewn into the armpits of t-shirts that had been washed with an odorless detergent before use. This technique has been used successfully in prior studies [4] , [14] , [50] ; the t-shirt serves to both hold the pads in place and protect them from outside contamination. Donors washed their bed linens and towels prior to the odor collection period with the same odorless detergent used for the t-shirts and then wore the t-shirt while sleeping alone at home for five consecutive nights. Before going to bed each night, donors washed their hair and bodies using odorless shampoo and soap to remove residues of exogenous odorous compounds. During the day, donors stored the t-shirts in sealed, odorless plastic bags to protect them from outside contamination. Donors were instructed to refrain from drinking alcohol, smoking, and eating spicy foods and other food products known to be excreted into our body odor for the duration of the odor collection period to avoid altering their natural body odor.

The t-shirt was returned to the experimenter after the fifth consecutive night of odor collection. The resulting body odor containing pads were each evaluated by the experimenter and if any trace of a potential exogenous odor was detected, or the pads were perceived to be lacking a discernible body odor, two additional individuals examined the body odor pads. Pads were included in the study only if the body odor was strong enough to be clearly detected and did not contain any perceivable exogenous odors (such as soap, smoke, perfume/cologne, or alcohol). When not in use, all stimuli were stored in a −80°C freezer to prevent decomposition [51] , and stimuli were always handled with disposable, odorless surgical gloves to prevent any possible contamination. Experimental stimuli were subsequently created by cutting each pad into equal size quadrants. These quadrants were used by combining one quadrant from each of four separate same-sex, same-age group individuals into “supra-donor” stimuli [48] . Six supra-donor stimuli (Y, M, and O of each sex) were assembled for each testing session. We used these so-called supra-donor stimuli to remove potential effects mediated by individual odor donors.

To avoid including individuals with olfactory dysfunction, participants’ ability to identify odors was assessed using the Sniffin’ Sticks 16-items Odor Identification test. A score of 10 or lower disqualified individuals with potential hyposmia [47] . After the olfactory identification screening test, participants performed three tasks, a perceptual ratings task, a forced-choice discrimination task, and an age labeling task. Within each task, the six supra-donor stimuli were presented in randomized order using 6 oz., wide-mouth glass jars; the same six odor stimuli were used for the three tasks of a testing session. Pad quadrants were arranged along the walls of the jar so that each pad quadrant was equally exposed. After a total of five subjects had been tested using the same set of stimuli, a new set of stimuli was made to prevent significant deterioration of the signal (see Figure S1 ). All testing occurred in a room specially designed for human chemosensory testing, which includes a ventilation system that continuously circulates room air to prevent the accumulation of volatiles. In all tests, a minimum inter-trial interval of 30 seconds was enforced between each trial, and breaks were given between each task to minimize odor habituation.

To assess potential differences in perceived pleasantness and intensity between the odor categories, participants rated perceived pleasantness of each body odor stimulus using visual analog scales [34] with the end anchors “Extremely unpleasant” (−5) and “Extremely pleasant” (5). Similarly, participants rated perceived intensity of each body odor stimulus using a labeled magnitude scale [35] with the end anchors “No sensation” (0) and “Strongest imaginable” (10). Stimuli were presented one at a time, and the order of age group presentation was randomized, both within each testing session and between participants.

Ability to discriminate between age groups was assessed with a two-alternative, forced-choice test. Participants were presented with two stimuli originating from different age groups and were asked to determine which of the two body odors originated from the older donor. Body odors were presented one at a time, and the order of age group presentation was randomized, both within each testing session and between participants. Both stimuli of a trial were presented for three seconds, and the second stimulus was presented immediately after the first (approximately 3 s in-between) to minimize the time interval for which odor stimuli needed to be remembered. Participants were not permitted to resample any stimuli. Body odor discrimination was assessed within each sex (Y/M, M/O, Y/O), and these six comparisons were repeated nine times each [52] , [53] .

The ability to estimate the ages of the body odor donors was also assessed. Participants were presented simultaneously with all six body odor stimuli and were asked to group them according to printed labels placed on the testing room table (“Young”, “Middle-age”, and “Old-age”). No restrictions on time or sampling frequency were given for this Age Labeling task.

Body odors have a very large inter-individual variance, and odor qualities in general, are difficult to assess objectively; indeed, some would say this is impossible. However, the free-sorting nature of the Age Labeling task allowed it to serve a second function: in addition to measuring participants’ ability to consciously label body odors by age, it also allowed us to assess whether the two body odor stimuli belonging to the same age category were grouped together more frequently than expected by chance, independent of whether they were assigned the correct age label or not. If an age group has a characteristic body odor quality, we would expect the two stimuli of that category to be grouped together rather than being assigned separate labels, and we expect that this would be independent of donor sex.

Statistical Analysis

The results of the discrimination tests were first converted to percentage correct values to allow the use of inference statistics on the underlying binary scale. To assess whether discrimination performance within each odor category differed from chance (50%), we used individual one-sample Student’s t -tests of percentage correct discrimination values. Differences in perceptual ratings were analyzed using mixed, repeated-measurements ANOVAs, separately for intensity and pleasantness, using a 2 (participant sex) ×3 (donor age group) ×2 (donor sex) design. Participant sex was entered as a between-subject factor, and donor age group and donor sex were used as within-subject factors. Subsequent Bonferroni posthoc tests were performed to statistically assess differences beyond main effects to control for multiple statistical comparisons. Discrimination performance was converted to a percentage correct discriminations value to correct for dichotomization. To assess statistical differences between stimuli, we used repeated-measurements ANCOVA, organized structurally as described above for perceptual ratings, but with two main differences: First, because our initial analyses of the perceptual ratings demonstrated that the largest perceptual difference between body odor groups was perceived intensity and not perceived pleasantness, intensity ratings for all age and sex groups were entered into the model as covariates (a total of six) to remove variance that could be explained by the intensity ratings. Please note that we refrained from adding the 6 pleasantness ratings as covariance factors because the unduly conservative nature of such analyses (a total reduction of our statistical power with 30% [−12 df]) would create a large risk of producing false negative results and conclusions. Second, because participants’ performance scores demonstrated near-significance on Mauchly’s Test of Sphericity ( p  = .058), all statistical values were submitted to Greenhouse-Geiser correction to avoid false positive results due to a skewed distribution. Age Labeling and Implicit Age Categorization task data (the latter described in detail below) were analyzed using chi-square (χ 2 ) contingency tests against a random sampling distribution created using Monte Carlo simulations (n = 1000) within the statistical program R.

Supporting Information

Intensity ratings by all individuals of all body odor stimuli. Smoothed Individual intensity ratings plotted over subject testing order. Y in legend indicates young, first M  =  middle-age, O  =  old, F  =  women, and second M  =  male; meaning that YF denotes ratings of a supra-donor stimuli originating from young women. Intensity ratings were performed on labeled magnitude scales with the end anchors “No sensation” (0) and “Strongest imaginable” (10).

https://doi.org/10.1371/journal.pone.0038110.s001

Acknowledgments

We wish to thank Dr. Steve Wang for providing help with statistical bootstrapping analyses.

Author Contributions

Conceived and designed the experiments: SM ARG JNL. Performed the experiments: SM ARG. Analyzed the data: SM JNL. Wrote the paper: SM ARG MJO JNL.

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Science News

These are the chemicals that give teens pungent body odor.

Carboxylic acids and steroids contribute fruity, musty and sandalwood-like scents

Researchers found two smelly steroids and a mix of pleasant and acrid carboxylic acids in samples of teenage body odor.

Olga Ihnatsyeva/Getty Images Plus

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By Skyler Ware

March 21, 2024 at 12:00 pm

Puberty changes just about everything. Bodies get taller, muscles get stronger — and often, body odor becomes more pungent. Now, scientists have identified some of the compounds that give teenagers their natural aroma.

Unlike that of infants and toddlers, teenage body odor has two smelly steroids and higher levels of carboxylic acids, researchers report March 21 in Communications Chemistry . Those chemicals form when bacteria break down armpit sweat and sebum, the oily secretions that keep our skin moist, and may contribute to the noticeable changes in BO throughout puberty.

“Body odor changes through development,” says chemist Helene Loos of Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany. “There is a really great diversity of different odor compounds that are present in body odors.”

Loos and colleagues collected body odor samples from 18 teens age 14 to 18 and 18 young children age 0 to 3 who had slept with cotton pads under their arms for a night. Separating the body odor into individual components revealed that young children and teens have over 40 compounds in common.

While some classes of chemicals showed no difference between age groups, the scents of carboxylic acids were more prevalent in teens. These compounds were a mix of pleasant scents, described by a panel trained to evaluate olfactory cues as fruity, soapy or grassy, and less-appealing ones that smelled cheesy, musty or goatlike.

Researchers also identified two steroids present only in the teens’ body odor. One, called 5α-androst-16-en-3-one, smells of sweat, urine and musk. The other, called 5α-androst-16-en-3α-ol, smells of musk and sandalwood.

A few components of scented products also turned up, despite participants avoiding deodorant and using unscented body wash and detergent for two days prior to the study.

Notably, some compounds known to contribute to strong body odor weren’t detected, says biochemist Andreas Natsch of Givaudan, a fragrance and flavor manufacturer headquartered in Vernier, Switzerland. Those chemicals might require different detection techniques, or they may show up more after exercising or working up a sweat ( SN: 7/13/21 ).

In future work, Loos hopes to look for those compounds and to study how BO changes at other stages of development ( SN: 5/30/12 ).

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Toddlers Smell Like Flowers, Teens Smell ‘Goatlike,’ Study Finds

Two musky steroids, and higher levels of odorous acids, distinguish the body odors of adolescents and tots.

By Emily Anthes

Few parents would describe the smells emanating from their adolescent children as redolent of sandalwood. But one of the distinct components of teenage body odor is a compound that evokes that warm, woody fragrance, according to a small new study , which compared the scents of adolescents to those of infants and toddlers.

Unfortunately, that’s just about where the good news ended for teenagers (and their parents). Although there were many similarities between the chemicals wafting from teens and tots, the differences tended to favor the younger children, whose body odor samples had higher levels of a compound with a flowery fragrance. Adolescents, on the other hand, produced a compound that smelled like sweat and urine and had higher levels of substances described as smelling cheesy, musty and “goatlike.”

The authors of the study, which was published in the journal Communications Chemistry on Thursday, would not go so far as to say that the results proved that adolescents smelled worse than babies. But the differences they documented “may contribute to a less pleasant body odor of teenagers,” said Diana Owsienko, who conducted the study as part of her doctoral research at the University of Erlangen–Nuremberg in Germany. (She is now a researcher at RISE Research Institutes of Sweden.)

Body odor is a complex blend of airborne chemicals, many of which are produced when sweat and sebum, an oily substance typically secreted through hair follicles, are broken down by skin microbes or react with other compounds in the air. The differences in scent between young children and teens probably stem from puberty-driven changes in sweat and sebum production, the researchers said.

The study was based on samples from 18 young children, who were age 3 or younger, and 18 adolescents who had gone through puberty. To collect the body odor samples, the scientists sewed small cotton patches into the armpits of T-shirts and body suits, which the children and teens wore overnight. (Participants were asked to refrain from using scented hygiene products and eating especially fragrant foods, such as onions and garlic, for 48 hours beforehand.)

In the lab, the scientists extracted and analyzed the chemical compounds that had permeated the patches, pooling together samples from multiple children in the same age group.

Odor samples from young children contained most of the same chemical ingredients as the samples from teenagers, the researchers found.

But there were two compounds, both steroids, that were present only in the adolescent samples. Sweat glands that do not become active until puberty secrete precursors to these compounds, which skin microbes convert into the steroids in question.

Characterizing scents is tricky. “There is no global consensus on how to describe odors,” said Helene Loos, who is an aroma and smell researcher at the University of Erlangen–Nuremberg and an author of the new paper.

Odor experts at the university had previously developed a standard vocabulary for characterizing the smells of different compounds, with an initial focus on food aromas. “We now also extended this flavor language to substances occurring in body odors,” Dr. Loos said.

Careful whiffs of the adolescents’ steroids revealed that one of the compounds smelled of sandalwood and musk. The other also had musk-like qualities, with the unfortunate additions of sweat- and urinelike aromas.

The teens also had higher levels of compounds called carboxylic acids. They included the musty, cheesy and goatlike substances — as well as some with less offensive aromas, variously described as earthy, fruity or waxlike.

Carboxylic acids are contained in sebum, which also includes other compounds that can be converted into carboxylic acids by microbes or various chemical processes. Sebum production increases during puberty.

The researchers theorize that, in combination, the two musky steroids plus the higher levels of carboxylic acids may explain why the body odor of adolescents can be off-putting to some people.

“I think it’s difficult to determine that one odor is always pleasant for everyone and to say another odor is always unpleasant for every person,” Ms. Owsienko said. “So this is an assumption from our side.”

Emily Anthes is a science reporter, writing primarily about animal health and science. She also covered the coronavirus pandemic. More about Emily Anthes

Jul 30, 2014

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Body Odor. By:hendricksen. Formulating questions. form: in what way sweat causes body odors to reek? function: how is sweat created inside our body and how is sweat able to give us body odors? causation: why is body odor always smell? C hange: how do body odor appear in our body?

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• human body odor
• bacterial activity
• armpit region
• responsibility

Presentation Transcript

Body Odor By:hendricksen

Formulating questions • form: in what way sweat causes body odors to reek? • function: how is sweat created inside our body and how is sweat able to give us body odors? • causation: why is body odor always smell? • Change: how do body odor appear in our body? • Connection: how is body odor able to get out from inside of our body? • Perspective: What is the main point of body odor? • Responsibility: what kind of possible tips that can make body odor gone for good and never appear in us again? • Reflection: how do we know if body odor is coming out?

Planning I will be using http://en.wikipedia.org/wiki/Body_odor as my primary resources and http://www.herbs2000.com/disorders/body_odor.htm As my secondary resources.

organizing • white hat(information): body odor is caused by skin glands excretion and bacterial activity. the human body odor is primarily the result of the apocrine sweat glands, which secrete the majority of chemical compounds needed for the skin flora to metabolize it into odorant substances. • yellow hat(positive impact): we are in our process of puberty so we can grow up and be more like an adult • black hat(negative impact): we get smelly and not much friends will get near us and our friends will tease us. • blue hat(thinking): i think that body odor will cause some serious problem because it makes us really smelly and not having many friends because of the smell • green hat(new points): the new points i think is to use a good quality soap and shampoo that can get rid of the smell. • red hat (feelings): i would feel lonely when i face body odor because it will drive my friends away.

Interpreting data • So, body odor is caused by genetics, armpit region and apocrine sweat glands, which secrete the majority of chemical compounds needed for the skin flora to metabolize it into odorant substances and it can be in animals to.

bibliography http://en.wikipedia.org/wiki/Body_odor http://www.herbs2000.com/disorders/body_odor.htm

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• Published: 02 April 2019

Body odors (even when masked) make you more emotional: behavioral and neural insights

• Cinzia Cecchetto   ORCID: orcid.org/0000-0001-9047-9884 1 , 2 , 3 ,
• Elisa Lancini 1 ,
• Domenica Bueti 1 ,
• Raffaella Ida Rumiati 1 , 4 &
• Valentina Parma 1 , 5 , 6  

Scientific Reports volume  9 , Article number:  5489 ( 2019 ) Cite this article

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• Olfactory cortex
• Sensory processing

Morality evolved within specific social contexts that are argued to shape moral choices. In turn, moral choices are hypothesized to be affected by body odors as they powerfully convey socially-relevant information. We thus investigated the neural underpinnings of the possible body odors effect on the participants’ decisions. In an fMRI study we presented to healthy individuals 64 moral dilemmas divided in incongruent (real) and congruent (fake) moral dilemmas, using different types of harm (intentional: instrumental dilemmas, or inadvertent: accidental dilemmas). Participants were required to choose deontological or utilitarian actions under the exposure to a neutral fragrance (masker) or body odors concealed by the same masker (masked body odor). Smelling the masked body odor while processing incongruent (not congruent) dilemmas activates the supramarginal gyrus, consistent with an increase in prosocial attitude. When processing accidental (not instrumental) dilemmas, smelling the masked body odor activates the angular gyrus, an area associated with the processing of people’s presence, supporting the hypothesis that body odors enhance the saliency of the social context in moral scenarios. These results suggest that masked body odors can influence moral choices by increasing the emotional experience during the decision process, and further explain how sensory unconscious biases affect human behavior.

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Introduction

Moral choices are most often explained as a result of emotional and cognitive processes 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . However, morality is primarily a social phenomenon, tightly dependent on the social context. In their Relationship Regulation theory (RR), Rai and Fiske 9 highlight the role of social context in shaping moral choices and posit that people are led by moral motives to evaluate and guide one’s own and others’ judgments and behaviors, according to moral rules developed within specific social relationships. In other words, people build a particular moral motive allowing to live in a specific social context while moral transgressions are defined as the circumvention of such specific relational prescriptions 9 . Recent empirical evidence supports this theory: for instance, participants’ moral acceptability of tradeoff scenarios can be affected by unconscious biases, such as intergroup prejudices and stereotypes, and the perception of different social groups influences the neural systems implicated in moral choices 10 .

Unconscious biases can influence moral decisions based on a variety of stimuli such as attitudes (such as dispositions towards people or places) 11 , implicit stereotypes (such as judging a person as attractive or unintelligent because is a cheerleader) 11 or somatic reactions (such as endocrine release or psychophysical reactions) 12 . However, this line of research has not yet considered the possibility of evaluating the effects of social information transmitted via sensory subliminal cues, such as odors. Humans transfer socially-relevant information, such as age, gender, health status, sexual availability and personal predispositions, via body (or social) odors 13 , 14 . Furthermore, odors – including people’s odors – are everywhere and we do not necessarily realize their presence consciously 14 , 15 .

The idea of using olfactory stimuli to investigate moral choices is not entirely new. Landy & Goodwin 16 argued how olfactory influences on morality are greater than those mediated by vision, the sense humans mostly rely on. Additionally, Schnall et al . 17 demonstrated that the presence of a disgusting odor toughens the judgment on vignettes without moral content. Also, as we have previously shown, the subliminal exposure to a neutral odor can bias moral choices towards options characterized by harm avoidance (deontological options) 18 . Generally speaking, a harm is justified, and to some extent forgiven, if it comes as the side-effect of a moral action carrying a greater benefit compared to an intentional harm with the same outcome 19 , 20 . All in all, odors are able to transfer social information and their effect on moral choices seems to modulate harm avoidance.

To our knowledge, previous studies have only explored the behavioral effects of olfactory contextual stimuli on moral choices 17 , 18 . However, whether and how the social context might impact moral decision making when induced via sensory subliminal stimulation, and the neural underpinnings of moral choices under the exposure of masked body odors, are still unknown. A meta-analysis showed that, in absence of odor stimulation, moral (vs. non-moral) choices were found to be associated with increased activations in primarily cognition-related areas (i.e., MTG, left and right middle temporal gyrus; rMFG, right middle frontal gyrus; rIFG, right inferior frontal gyrus) and primarily emotion-related areas (i.e., cingulate gyrus, left precuneus) 21 . However, the way in which moral dilemmas are formulated modulates the competition between the fast, automatic emotional response and the slow, deliberative cognitive system. As previously shown, instrumental dilemmas (Footbridge-type dilemmas) 22 recruit emotion-related brain areas such as medial prefrontal cortex, posterior cingulate cortex/precuneus, amygdala, and brain areas involved in “theory of mind” such as the temporoparietal junction (TPJ) and angular gyrus 1 , 2 , 4 . On the other hand, accidental dilemmas (trolley-type dilemmas) are associated with activations in neural areas involved in working memory and cognitive control, such as the dorsolateral prefrontal cortex and inferior parietal lobe 1 , 2 , 4 .

While the impact of the exposure to body odors on the neural underpinnings of moral choices still remains unexplored, we are now aware that processing body vs. common odors 23 rely on distinct neural pathways, in line with what occurs when social information is presented through other sensory modalities (e.g., Schupp et al . 24 for vision and Belin et al . 25 for audition). Processing body odors recruits the occipital cortex, active when either visual stimuli or socially-relevant stimuli are cross-modally presented 26 , the angular gyrus, responsive to human body related information 27 but also involved in social cognition and multisensory integration; and the anterior and posterior cingulate cortex, previously found implicated in emotion regulation 28 , 29 and self-reflective processes 30 . What still remains to be clarified is whether these regions are also involved in the perception of human body odors during a concurrent cognitively demanding task (such as making moral decisions). If this were the case, we would expect a reduction in the activation of OFC or of the higher order areas described (e.g., posterior cingulate cortex) as a result of a reduced attention for sensory analysis, in line with the reduced activation of amygdala 31 or piriform cortex 32 , 33 observed when complex judgments are performed during odor perception.

In the present work, we hereby tested whether and how introducing a social context through masked body odors impact the behavioral and the neural correlates of moral choices. The aims of the study were the following: (1) to test whether subliminally presented body odors have a selective effect on incongruent moral dilemmas (real dilemmas) or generalize to different types of decision-making scenarios (congruent or fake dilemmas); and (2) to investigate whether and how body odors impact harm avoidance decisions. In the present functional magnetic resonance imaging (fMRI) study, participants were asked to answer to 64 moral dilemmas during the presentation of a fragrance neutral in pleasantness (masker) or to a body odor concealed by the same fragrance (masked body odor). The main dependent variable was the type of moral choice made, which could be utilitarian , if participants decided to execute harmful actions in order to save people, or deontological , if participants decided not to cause harm to not violate societal norms, even if the harm is meant for a greater good 2 , 19 . To explore whether the effect of the masked body odor is modulated by the dilemmatic nature of the presented scenario, half of the dilemmas were congruent, meaning that cognitive and emotional processes converged towards the same deontological action so that they were fake dilemmas, and half were incongruent dilemmas in which the two processes diverged, so they were real dilemmas 34 . Moreover, to clarify the modulation of the type of harm, half of the dilemmas were instrumental (dilemmas in which the harm is deliberate) and the other half were accidental (dilemmas in which the harm is a side effect).

We hypothesized that the presence of body odor would induce the participants to perceive the people involved in the scenario as more concrete, real. If that were the case, then participants are expected to be more prone to follow societal norms not to harm people. We anticipated this effect to be stronger than the increase of deontological answers shown when a neutral odor is presented 18 . Since it has been shown that when dealing with incongruent (compared to congruent) dilemmas, individuals were found to be more willing to provide utilitarian answers 34 , we expected such trend to be reduced in the presence of the masked body odor. Moreover, as in a previous study 18 we observed that the presence of a neutral odor increases the number of deontological answers specifically for instrumental dilemmas, here we expected the presence of the masked body odor to result in an increment of deontological answers for such dilemmas.

With respect to the neural underpinnings, we hypothesized that the processing of incongruent (compared to the congruent) dilemmas would be associated with brain regions commonly implicated in this type of task, such as the amygdala, the ventro-medial prefrontal cortex (vmPFC 1 , 35 , the temporo-parietal junction 36 and the precuneus 21 . Additionally, we predict that the presence of the body odor would favor activations in areas commonly associated with social information, including body odor processing, such as the angular gyrus, occipital cortex, and the anterior and posterior cingulate cortex 14 , 23 . We further hypothesized that when processing dilemmas that describe intentional harm, emotional brain areas, such as the cingulate gyrus or precuneus, would be more strongly activated. We expected that these emotional areas would be more strongly activated in the presence of the masked body odor, even when processing accidental dilemmas, usually associated with cognitive neural areas. However, given the innovative nature of this research, we had no clear predictions as to the specific neural areas to be recruited, and we therefore explore whole-brain activations with respect to this contrast.

Materials and Methods

Ten healthy, heterosexual males donated their body odors in two different days (age: 26.3 ± 3.6 years old (mean ± SD); range = 20–31). Male donors were chosen based on the greater intensity of their body odor axillary secretions 37 . The donors reported: (i) to be non-smokers 38 ; (ii) not to have health issues or to undergo drug treatment known to be related to olfactory alterations; (iii) to have an age ranging from 18 to 35 years old. Informed written consent was obtained from each donor. Each donor agreed to follow behavioral, nutritional (i.e., no alcohol, smoking, food altering the natural body odor) and hygiene instructions throughout the collection session (adapted from) 14 . The medium of body odor collection was a t-shirt, previously washed with an odorless detergent (Liquid Detergent ECOR with no Perfume and essential oils, ECOR 27094). T-shirts were worn by donors for 12 consecutive hours during the day, right after having taken a shower using fragrance-free body wash and having dried themselves with towels washed with the same odor-free detergent used to pre-wash the t-shirts. Donors collected their body odors on separate t-shirts for each day of collection for a total of two days. Odorless plastic bags were provided to each donor to store each of their t-shirts before bringing them to the lab, the day after each collection period 23 , 39 . Samples were perceptually evaluated for odor contamination (e.g., alcohol, smoke, fragrance, food) and for body odor detectability by one to three trained experimenters. All samples were then stored in a −80 °C freezer to prevent sample deterioration 40 .

Participants

The original group of participants was composed of 30 women. The rationale for testing only women is based on the evidence that women show a greater preference for social emotional stimuli 41 , also when presented in olfactory form 42 . The participants followed the same criteria as the donors, and additionally, they had to score at the 16-item Sniffin’ Sticks Identification subtest of the Sniffin’ Sticks Extended test above 10 43 as well as presenting a regular menstrual cycle 44 .

No depression or heightened sensitivity to disgust (Disgust Scale) 45 was revealed. Two participants were removed from the study because of possible clinical problems. The final sample included 28 healthy, heterosexual, right-handed women aged between 19 and 34 (23.7 ± 4.2 years), who were normosmic (TDI score: 13.4 ± 1.5, range = 11–16), and whose STAI state score before the task was within the normal range (STAI state score: 33.7 ± 4.3, range = 24–42). Participants were instructed to not eat or drink anything but water one hour prior to testing, and to not wear any scented products on the day of testing. The SISSA Ethics Committee approved the study, which is in accordance with the Declaration of Helsinki and an informed written consent was obtained from each participant.

General procedure

At the beginning of the experiment, participants were seated in a quiet room and they were instructed about the experiment. Then participants performed the odor identification test 43 and they completed the State questionnaire of the State-Trait Anxiety Inventory (STAI-S) 46 . Anxiety state data were collected because previous literature has shown that moral choices are modulated by individual variability in anxiety 18 , 47 , 48 . To test whether the masking procedure supposed to cover the body odor produced the expected perceptual impact to the same extent across olfactory conditions, participants were asked to rate intensity, pleasantness and familiarity of the masker, masked body odor and clean air before and after the moral decision-making task. The three tasks were all performed inside the scanner in order to override the possible confounding effects of the MRI scanner setting. The procedure of the odor-rating task and of the moral decision-making task was similar to the one applied in previous study 18 (see Supplemental Information for details about the two tasks). Then, outside the scanner, participants completed again the STAI State questionnaire 44 . See Fig.  1 for an overview of the experimental procedure.

Overview of the experimental procedure. ( A ) Overview of the experiment session; ( B ) Overview of a single trial of the moral decision-making task. See Fig.  S1 of the Supplementary Information for an overview of the type of moral dilemmas and odor conditions.

Odor stimuli

Two odor conditions were presented within participants. One set of dilemma alternatives (N = 32) was presented during the exposure to an emotionally neutral, rather unfamiliar odor (aka, masker odor ; 200 μL of cedarwood oil, Sigma-Aldrich), as determined via pilot studies (see Supplementary Information of 49 for detailed descriptions of the odor pilots) and as confirmed by previous study 18 . The masker odor was applied to equally-sized quadrants of cotton white t-shirt previously washed with the same detergent used for the t-shirts worn by the donors. The second set of dilemmas alternatives (N = 32) was presented during the exposure to the masked body odor . The masked body odor was prepared by including in a glass jar four donated t-shirt quadrants (supradonor) chosen from all those collected from the 10 donors and one clean t-shirt quadrant on which we applied 200 μL of masker odor 50 . The masking procedure was used to simulate the hygiene products usually used with the goal of making the paradigm more ecologically valid 51 . As customary in human body odor research 14 , 52 , 53 , 54 , 55 , each recipient smelled one supradonor stimulus across all dilemma trials, but in order to reduce the stimuli similarity 52 , the combination varied in terms of the axilla the sample came from and the day at which it was collected. The order of the two odor conditions presentations was randomized across subjects and across the four blocks of the moral decision-making task.

Odors were presented bi-rhinally in a temporally-precise, square-shaped manner using a computer-automated olfactometer 56 . A low bi-rhinal flow rate of 1.0 L/m (a total of 0.5 L/m per nostril) was used to prevent irritation of the nasal mucosa over time 56 , 57 . Odor stimuli were delivered directly to both participants’ nostrils from a nasal manifold, attached to the participant’s chest by means of a chest strap, connected to the olfactometer via Teflon tubing.

Odor rating task

A green fixation cross lasting for 0.5 s preceded each odor presentation. The odor presentation lasted for 4.0 s and was accompanied by a black screen. Subsequently, a white screen was presented for 6.0 ± 0.1 s (mean ± SD) during which participants were asked in succession and in a random order to answer the following questions: “How intense was the odor you just smelled?”, “How pleasant was the odor you just smelled?”, and “How familiar was the odor you just smelled?”. During question presentation, clean air was released to minimize odor residuals 56 . Perceptual ratings for odor intensity, pleasantness, and familiarity were collected on a 10-cm computerized Visual Analogue Scale (VAS), ranging from “not at all” to “very much”. Participants were instructed to answer even if they did not perceive any odor. The odor rating task was performed inside the scanner to reduce the time of the experimental session, but without collecting functional MRI data.

Moral decision-making task

The 4CONFiDE moral set described in Cecchetto et al . 20 was reshaped for this study to include congruent and incongruent dilemmas. A total of 64 dilemmas was presented, 32 congruent and 32 incongruent. Furthermore, half of the congruent and incongruent dilemmas were accidental and the remaining instrumental. Each dilemma type was presented in 16 alternative versions to allow for the presentation of the same factor combination in both odor conditions. The order of presentation of the dilemmas was randomized across participants to exclude any presentation order effects on moral decision-making (see Fig.  S1 in the Supplementary Information for a visualization of the features of the dilemma set).

Each dilemma was presented on two subsequent screens. The first screen described the scenario, in which a danger threatens to kill a group of persons, and a hypothetical action would save these people but cause the death of another person. The second screen presented the question Do you…[action verb] so that…? Participants had to choose between four options: “I certainly do it”, “I do it”, “I do not do it”, and “I certainly do not do it”. The first two choices are held to be utilitarian, as they maximize overall utility (i.e., saving more lives), whereas the latter two were non-utilitarian (deontological).

Before starting the moral decision-making task, participants performed two practice trials. An Italian version of the instructions suggested by Christensen et al . 19 and previously used in Cecchetto et al . 20 was administered.

See Fig.  1 for an overview of the moral decision-making task. Each trial began with a black cross that was displayed for 5.0 ± 0.3 s. Then, a green cross was presented for 1.2 ± 0.2 s and the odor delivery started. Subsequently, the scenario was presented for 22.0 s. The scenario presentation was combined with the odor presentation. Afterwards, the question slide was presented together with the releasing of clean air to minimize odor residuals 56 . The four choices were displayed below the question. Participants had maximum 5.0 s to answer. After the answer a black cross was presented for 5.0 s.

The 64 dilemmas were divided into four blocks that corresponded to four scanning runs. During each block, 16 trials balanced for moral dilemmas types and odor conditions, were presented in randomized order. Participants were allowed to take a short break at the end of each run while lying in the scanner. Dilemmas were presented using a black font color (font: Calibri, size: 24) against a white background. Stimulus presentation was delivered with E-prime 2.0 software (Psychology Software Tools, Pittsburgh, PA).

Behavioral data analysis

Frequency analysis was performed on the four response options to see whether the number of each option changed based on the odor condition. Since no significant differences were found among the four response options in relation to odour condition, we collapsed them for the subsequent analyses.

Behavioral data were analyzed with linear mixed-effects models (LMMs) 58 using R (version 2.10.1; http://www.r-project.org/ ) and in particular using the lme function ( nlme package; https://cran.r-project.org/web/packages/nlme/nlme.pdf ) for continuous variables and the glmer function ( lme4 package; http://cran.r-project.org/web/packages/lme4/index.html ) for binary variables (deontological or utilitarian answer). To account for individual differences (e.g., some people are more “deontological” than others), participants were included in the models as random factors. To avoid a warning of non-convergence, an optimizer (bobyqa) was applied 59 . Results with and without the optimizer are not significantly different ( https://github.com/lme4/lme4/blob/master/misc/notes/release_notes.md ). Estimates on the choice between utilitarian and deontological responses were based on an adaptive Gaussian Hermite approximation of the likelihood with 10 integration points. For odor ratings, models with odor and session were tested. For moral choice, two models were performed: the first included odor, as the main variable of interest of our analysis, and congruency. The second model included odor and intentionality and it was performed considering only incongruent dilemmas.

Outliers in reaction times were determined by means of the outliers-labelling rule 60 . From a sample of 1792, 127 trials were removed for no response (N = 127/1792, 7.08%), and 43 trials were removed because of extremely long choice reaction times (>2.6 s; N = 43/1665, 2.58%; mean of reaction times is 820.8 ± 507.2 s). Conditions have equivalent final samples of trials (Masker odor = 810, Masked Body odor = 812; X 2 1  = 0.0025, p = 0.96).

MRI data acquisition and pre-processing

A 3 Tesla Philips Achieva whole-body MR Scanner at the University Hospital of Udine (ASUI Udine, Italy), equipped with an 8-channel head coil, was used for MRI scanning. Head movement was minimized through cushioning within the coil. Functional volumes were obtained using a whole-head T2 * -weighted echoplanar image (EPI) sequence (repetition time [TR] = 2.5 s, echo time = 35 ms, flip angle = 90°, 28 transverse axial slices with interleaved acquisition, 3.50 × 3.59 × 4.00 mm 3 voxel resolution, field of view = 230 × 230 mm 2 , acquisition matrix = 68 × 62, SENSE factors: 2 in the anterior–posterior direction). The number of volumes acquired varied for each participant and run given the task duration based on participants’ reaction times (mean number of volumes per run = 260 ± 4.6, range = 153–270). Anatomical images were acquired during the final odor rating task as 180 T1-weighted images (0.75 mm slice thickness). Stimuli were viewed through VisuaStim Goggles system (Resonance Technology) mounted to the head coil, which was adjusted on each participant’s vision. Responses were made and recorded through one MR-compatible response pads (Lumitouch, Lightwave Medical Industries, Coldswitch technologies, Richmond, CA) using the right hand. To minimize influences of breathing effects, participants were instructed and trained to maintain a constant and normal breathing rate. Due to technical problems, images from the first session of one participant and the second session of another participant were removed from the analysis.

Data were analyzed with SPM12 (Wellcome Trust Centre for Neuroimaging, London, UK). All functional volumes were spatially realigned to the first volume, slice- time corrected, segmented in gray matter, white matter and cerebrospinal fluid tissues, spatially normalized to the standard EPI template, and smoothed using a Gaussian kernel with full width at half maximum (FWHM) of 8 mm 3 . Movement-related variance was analyzed using the Art toolbox ( www.nitrc.org/projects/artifact_detect ). For each run, outlier scans were identified based on the TR-to-TR composite motion more than 2 mm and/or considering whether the scan-to-scan global BOLD signal normalized to z-scores deviated from mean more than z = 3. The time-points identified as outliers were regressed out as separate nuisance covariates in the first-level design matrix. All participants displayed a percentage of outlier scan inferior to the cutoff (25%), therefore no one was excluded from the analyses and all trials were retained.

fMRI data analysis

Two separated fMRI data analyses were carried out: in the first analysis, odor conditions and congruency of dilemmas were considered to explore whether the effect of masked body odor was modulated by the dilemmatic nature of the presented scenario; in the second analysis, which was performed only on incongruent dilemmas, odor conditions and intentionality as the type of dilemmas were considered to investigate the effects of masker body odor on the processing of different types of harm.

Statistical analyses were performed using a general linear model (GLM) approach. In the first-level analysis, data were analyzed separately for each participant. In each trial, four events were modelled: the presentation of clean air, of an odor, of the scenario combined with an odor and, of the slide including the question. The duration of each of these events was set to 0 except for the scenario presentation, which was set to a fixed time of 22.0 s. The combination of these four event types with dilemma congruency (congruent vs incongruent) or dilemma intentionality (accidental vs instrumental) and the two odor conditions (masker vs masked body odor) led to a total of 16 regressors for each run. The six motion parameters were also included as regressors of no interest in the design matrix. All regressors were convolved with a canonical hemodynamic response function. Low-frequency signal drifts were filtered using a cutoff period of 128.0 s. As a next step, at the individual level, contrast parameters were estimated for all the 16 regressors of interest, averaged across the four runs. Subsequently, at the second-level analysis, 4 contrast images of the event scenario presentations from the combination odor with congruency or intentionality of each participant were submitted to a flexible factorial design, with subject as random factor, odor conditions and congruency or intentionality as fixed factors, to assess neural activations of the dilemma processing during the exposure to the odor. Later, the 4 contrast images were entered to linear contrasts of the repeated measure ANOVA with two within-subject factors to investigate main effects and interactions. To identify the neuronal substrates of single odor condition or single dilemma type, simple main effects (i.e., [masker odor – masked body odor] for each odor condition and each dilemma type separately) were analyzed. To investigate whether odor conditions affect neural activity related to moral dilemma processing, we performed a dilemma type (i.e. congruent/incongruent or accidental/instrumental) by odor condition (masker odor/masked body odor) interaction at group level. Moreover, to clarify whether the neural underpinnings involved in the masker body odor effects for one dilemma type (i.e. incongruent or accidental) are shared by the opposing dilemma type (i.e. congruent or instrumental), exclusive and inclusive conjunction analyses were performed between the neural areas recruited for the interactions [odor × congruency or intentionality].

Finally, in order to investigate the relationship between brain activations and moral choices, the mean beta values of the activated clusters were extracted using the REX toolbox (Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, MA) and simple correlation analyses were performed with the percentage of utilitarian responses.

Whole-brain analyses were thresholded at p < 0.05, family-wise error (FWE) cluster-level corrected for multiple comparisons across the whole brain. The AAL2 toolbox 61 , 62 was used to guide the labelling of the activated clusters.

Masked body odor and masker are perceptually similar

We first tested whether the masking procedure applied to cover the masked body odor had the expected perceptual impact and rendered the olfactory conditions equivalent in their basic perceptual dimensions. The LMM on intensity ratings (clean air: 2.45 ± 0.13 points; masker: 5.83 ± 0.18 points; masked body odor: 6.10 ± 0.16 points; see Fig.  2A and Table  1 ) revealed that both the masker and the masked body odor were perceived as significantly more intense than clean air ( p  < 0.001; reference factor: clean air), but no significant difference was found between the masker and the masked body odor ( p  = 0.48; reference factor: masker). A difference emerged when looking at the effect of session (pre moral decision-making task: 5.23 ± 0.21 points; post moral decision-making task: 4.56 ± 0.20 points; p  = 0.024): odors were rated as less intense during the second session compared to the first session suggesting that participants might have adapted during the task (Dalton, 2000).

Distribution of participants’ odor ratings. The black dots represent single data points, whereas the box-plot represents the interquartile range of each distribution, with the thick black horizontal bar corresponding to the median. Each box-plot is surrounded by a violin plot representing the smoothed distribution of data. Significant differences (p < 0.05) are indicated with a star.

The LMM on familiarity ratings (clean air: 3.78 ± 0.14 points; masker: 5.61 ± 0.20 points; masked body odor: 5.91 ± 0.17 points; see Fig.  2B and Table  1 ) showed that both the masker and the masked body odor were perceived as significantly more familiar than clean air ( p  < 0.001; reference factor: clean air), but no significant difference was found between the masker and the masked body odor ( p  = 0.40; reference factor: masker). No significant differences were found between the ratings performed before and after the task ( p  = 0.32; reference factor: pre).

The LMM on pleasantness ratings (clean air: 4.48 ± 0.12 points; masker: 4.89 ± 0.16 points; masked body odor: 4.58 ± 0.18 points; Fig.  2C ) showed no significant differences across the three odor conditions. Moreover, no significant differences were found between sessions. Please, refer to Table  1 for descriptive data.

State anxiety is increased at the end of the task

A Wilcoxon test (W = 148801, p  < 0.0001) determined that participants’ state anxiety was increased at the end of the task (34.36 ± 6.45 points, range = 22–48) as compared to its beginning (33.67 ± 4.33 points, range = 24–42; see Fig.  S2 in the Supplementary Information).

Irrespective of odor condition, incongruent dilemmas produce more utilitarian responses

First, the model including odor conditions, congruency and the interaction between them was performed (see Table  2 for descriptive data of single parameters). There was a significant effect of congruency on moral choice: the likelihood of choosing the utilitarian option increased when dilemmas were incongruent (z = 10.08, p  < 0.001). In other words, when cognitive and emotional processes diverge (real dilemmas), more utilitarian answers are produced than when cognitive and emotional processes converge (fake dilemmas). No significant effects were found for the main effect of odor condition or for the interaction odor × congruency.

Irrespective of odor condition, accidental dilemmas produce more utilitarian responses

Considering the results of the previous model, we tested the effect of odor conditions, intentionality and the interaction between these two factors on incongruent dilemmas only (see Table  3 for descriptive data of single parameters). A significant effect of intentionality emerged (z = −0.43, p  < 0.001): in incongruent dilemmas, the likelihood of choosing the utilitarian option increased when dilemmas were accidental (vs instrumental). The odor condition, alone or in interaction, did not affect the type of moral choice made.

fMRI brain activations

Areas involved in moral cognition are selectively activated by incongruent dilemmas.

The processing of real dilemmas (contrast incongruent vs congruent dilemmas) revealed activations in the left middle frontal gyrus, left inferior parietal gyrus and bilateral precuneus (see Table  4 and Fig.  3A ). The correlation analysis performed between beta values and percentage of utilitarian answers did not show significant results. No significant activations emerged when considering the processing of fake dilemmas (congruent vs incongruent dilemmas).

Brain activation maps showing significant cluster of activations for ( A ) Incongruent >Congruent: significant activations in the left middle frontal gyrus, left inferior parietal gyrus and bilateral precuneus; ( B ) Masked body odor >Masker: significant activations in the left supramarginal gyrus; ( C ) Incongruent (masked body odor >masker) >Congruent (masked body odor >masker): significant activations in the left supramarginal gyrus. Statistical maps are derived with a threshold of p  < 0.05 FWE corrected and superimposed on a standard T1 template. Color scale represents t statistics. Image labels: L = left, R = right.

Activation in visual areas tracks the utilitarian responses to incongruent dilemmas when exposed to the masker odor only

The presence of the masked body odor (vs the masker odor) during the presentation of both incongruent and congruent dilemmas was accompanied by activations in the left supramarginal gyrus (see Table  4 and Fig.  3B ). In contrast, the presence of the masker odor (vs the masked body odor) activates the bilateral calcarine cortex, the left middle occipital gyrus, the right precuneus, the left lingual gyrus and the left posterior cingulum (see Table  4 ). The beta values extracted from the cluster including the bilateral calcarine cortex and the left middle occipital gyrus significantly correlate with the number of utilitarian responses to incongruent dilemmas when exposed to the masker odor ( r  = 0.48, p  = 0.009). No other significant correlation between behavioral responses and neural activations emerged.

The masked body odor during incongruent dilemmas is associated with activations in the left supramarginal gyrus

To identify whether the brain regions that are active components in the masked body odor effect for the incongruent dilemmas are shared also for the masked body odor effect in congruent dilemmas, exclusion and inclusion conjunction analyses were performed between the areas recruited for the interaction “masked body odor and incongruent dilemmas” and for the interaction “masked body odor and congruent dilemmas”. The exclusion conjunction analysis for [incongruent (masked body odor >masker) >congruent dilemmas (masked body odor >masker)] showed that the left supramarginal gyrus was significantly recruited only when the masked body odor was presented during the processing of incongruent dilemmas (see Table  4 and Fig.  3C ). No significant correlations were found between the extracted beta values and percentage of utilitarian answers in this contrast. The inclusion conjunction analysis and the opposite exclusion conjunction analysis did not reveal any significant results.

Emotional areas are involved in instrumental vs accidental incongruent dilemmas

To evaluate the effect of intentionality, only incongruent dilemmas were considered. Processing accidental (vs instrumental) dilemmas significantly activated the left lingual gyrus, left fusiform gyrus, the left inferior occipital gyrus and the left middle occipital gyrus (see Table  5 and Fig.  4A ), whereas processing instrumental (vs accidental dilemmas) was related to significant activation in the bilateral precuneus (see Table  5 and Fig.  4B ). No significant correlations with behavioral responses were retrieved.

Brain activation maps showing significant cluster of activations for ( A ) Accidental >Instrumental: significant activations in the left lingual gyrus, left fusiform gyrus, the left inferior occipital gyrus and the left middle occipital gyrus; ( B ) Instrumental >Accidental: significant activations in the bilateral precuneus; ( C ) Accidental (masked body odor >masker) >Instrumental (masked body odor >masker; significant): significant activations in the left superior and inferior parietal gyrus and in the right angular gyrus. Statistical maps are derived with a threshold of p  < 0.05 FWE corrected and superimposed on a standard T1 template (Coronal and sagittal views are displayed). Color scale represents t statistics. Image labels: L = left, R = right.

The masked body odor during accidental dilemmas is associated with activations in the left parietal and right angular gyri

To clarify whether the brain regions that are active components in the masked body odor effect for the accidental dilemmas are shared also for the masked body odor effect in instrumental dilemmas, conjunction analyses were performed between the neural areas recruited for the interaction “masked body odor and accidental dilemmas” and for the interaction “masked body odor and instrumental dilemmas”. The exclusive conjunction analysis for accidental (masked body odor >masker) >instrumental (masked body odor >masker) showed significant activations in the left superior and inferior parietal gyrus and in the right angular gyrus. The inclusive conjunction analysis and the opposite exclusion conjunction analysis did not reveal any significant results suggesting that the masked body odor modulated only the processing of accidental dilemmas (see Table  5 and Fig.  4C ). The correlation analysis between the beta values extracted and the percentage of utilitarian responses did not reveal any significant results.

Previous research suggests that moral rules are developed within specific social-relational contexts that, in turn, play a critical role in shaping moral choices 9 , 10 . As human body odors are powerful messengers for socially-relevant information 63 , able to modulate the behavior and neural processing of the receiver 13 , 14 , 23 , 39 , 53 , 54 , 55 , we hypothesized that body odors might affect moral choices through the modulation of the perceived social context (i.e., by inducing the perception of the real presence of a person). With this in mind, we asked participants to decide their course of action to moral scenarios while exposed to a neutral fragrance (masker) or to a body odor hidden by the same masker odor (masked body odor). The analysis of the neural correlates revealed that the exposure to the masked body odor: a) modulates the activity in the brain areas involved in the processing of incongruent (real) dilemmas, but not in those involved in the processing of congruent (fake) dilemmas; and b) increases the activations in areas processing sensory and emotional information when incongruent accidental dilemmas are presented.

In our study, we investigated whether masked body odors influence any decision-making task or whether the influence is specific to moral dilemmas, as we had anticipated. The analysis we performed revealed that the masked body odors moderate the neural responses only related to incongruent (but not congruent) dilemmas, increasing the involvement of the left supramarginal gyrus. While presented with a real (incongruent) moral dilemma, the participants immediately experience a negative emotional reaction at the thought of provoking harm: the final decision will be deontological providing that this emotional reaction is sufficiently influential, and that participants have limited time and cognitive resources to make their decision. On the other hand, if participants have enough time, motivation and cognitive resources, they will have the possibility to engage in cognitive deliberation about costs and benefits, in which case the emotional response may be overshadowed, resulting in an utilitarian response to the dilemma 2 , 34 . The information of the masked body odor might interfere with this conflict enhancing the neural pathways that promote prosocial behavior 64 , therefore emphasizing the emotional processing of the sensory information, and facilitate the emergence of deontological responses. This multisensory integration of the social and sensory information provided by the masked body odor, and the emotional information provided by the moral dilemmas involve the left supramarginal gyrus, close to the angular gyrus 1 , one of the neural areas previously found to be associated with the processing of body odors 2 , 3 . The supramarginal gyrus has been often considered as part of the temporo-parietal junction (TPJ) - a neural area typically associated with self-awareness and body-related information processing 4 , 5 and, as such, often involved in tasks of theory of mind 5 , 6 , empathy for pain 7 and in the perception of anxiety body odors 8 . Importantly, these aspects become relevant when considering a body odor in the context of moral dilemmas. Indeed, the centrality of the left supramarginal gyrus in multisensory integration processes has recently been supported in a study that identifies this brain area as an important node for the olfactory-visual processing 9 .

Since in the fake (congruent) dilemmas there is no conflict between emotional and cognitive aspects of the decision (i.e., the benefits do not balance the costs), the social information about the presence of a person becomes irrelevant for the decision itself.

Moreover, in the present study, we clarified whether the masked body odor effect is modulated by the type of harm, being it deliberate (instrumental dilemmas) or an inadvertent effect (accidental dilemmas). Previous studies showed that the accidental harm is judged as being more morally acceptable, it receives higher percentage of utilitarian answers, and it engages lower emotional reactions compared to intentional harming 4 , 64 . Our results are in line with this literature: instrumental dilemmas presented higher percentage of deontological answers and recruited neural areas involved in emotional processing (e.g., precuneus) when compared to accidental dilemmas. Interestingly, the masked body odor seems to moderate the processing of the accidental dilemmas by enhancing the activation of the angular gyrus, which is usually associated with social cognition, multisensory integration and “theory of mind” 27 , and the inferior parietal gyrus, which is important for self-other discrimination 65 . This result seems to support our hypothesis that the presence of a body odor can induce the participant to perceive the social context of the dilemmas as more concrete, as if the odor signaled the presence of a real person, and not just of a hypothetical context. The reason why the masked body odor seems to selectively affect the processing of the accidental and not of the instrumental dilemmas may be due to the higher emotional involvement of the instrumental dilemmas, which prevents the participants to consider the additional emotional information provided by the odor.

The present fMRI data replicate and extend previous findings concerning the neural networks recruited by social odor processing 14 , 15 , 23 . Besides replicating the enrollment of the left supramarginal gyrus, as discussed above, we also showed major activity in the left hemisphere areas. This result, in line with previous studies 23 , 66 , supports the hypothesis that olfactory-mediated affective processes are lateralized in the left hemisphere 67 .

In our study, the body odor was masked by a neutral odor. This masker was applied to simulate the hygiene products usually used to cover the natural body odors we produce and to make the paradigm more ecologically valid 51 . Additionally, it allowed studying the effects of the body odor when they are unconsciously perceived. As seen in previous work 18 , odor effects can emerge irrespective of perceiving the presence of an odor; moreover, masking the body odor limited the inter-individual differences in odor intensity and pleasantness. Such differences can significantly affect decisions, as it seemed in the previous cases when intensity and pleasantness differences across odor conditions were evident 17 , 18 . Here we succeeded in making these conditions perceptually similar for intensity, pleasantness and familiarity, removing the possible confounding effect of these factors on the differences in the moral decisions.

To our knowledge, this is the first study that tests the effects of masked body odors on the neural underpinning of moral decision-making. The present study has some limitations for which future studies are necessary. First, it was designed around a moral decision-making paradigm based on the presentation of moral dilemmas, which felt dilemmatic as the participants’ anxiety levels raised at the end of the task. The use of this sort of dilemmas has been previously criticized (e.g.) 55 , 64 , 68 : (i) dilemmas are described in lengthily written texts, which increase the time needed by the participants to process each stimulus; (ii) to make dilemmas credible they cannot be repeated; (iii) the conceptual factors cannot be analyzed separately, but have to be intermingled in each dilemma. These aspects reduce the possibility to present large numbers of trials, therefore limiting the power of the study. To overcome these issues, we have used here a standardized, culturally-equivalent moral set, specifically designed for imaging experiments, that shows high consistency across the different dilemmas 20 . Moreover, to increase the power of our observations, we based the investigation on a theoretically-motivated interest for one conceptual factor (Intentionality). Despite these efforts, the behavioral analysis failed to reveal any significant mean effects of the odor conditions or significant interactions with odor and dilemma congruency or intentionality. One proposed explanation is that the dilemmas were designed to simultaneously assess also other conceptual factors, such as personal force, benefit recipient and evitability. It is for future studies to clarify whether the masked body odor elicits different effects on moral choices when different conceptual factors are considered (see for example) 69 . Second, the participants’ respiratory patterns were not recorded and incorporated in the fMRI data processing. Although this is common practice in many olfactory neuroimaging studies 70 , 71 , we invite future studies to investigate whether the breathing patterns to human body odor can have an impact on the moral decisions made. Third, only one common odor (cedarwood oil) has been used as masker, and the results cannot be generalizable to all common odors. Fourth, future studies should also increase the sample size to allow the comparison of masked body odors effects in women and men and evaluate potential sex-related effects. Lastly, it would be interesting if future investigations would be extended to clinical populations with a deficit in emotion processing, such as patients with lesions in the ventromedial prefrontal cortex 72 , or non-clinical populations with emotional deficiencies, such as those with a lack of empathy or with high levels of alexithymia 73 , 74 , to examine whether the masked body odor effects on moral decision-making can overcome the usual tendency in this population to give higher percentage of utilitarian answers 74 .

To conclude, the value of these results is highlighted by the consideration that most of the moral decisions, from everyday choices to choices that we are forced to make under unexpected circumstances, are made in the presence of other people. Starting from the theory proposed by Rai and Fiske 9 , which advanced the hypothesis that actions and outcomes should be considered in the context of specific social relationships, indeed any action - including violence and impure acts - can be perceived as morally acceptable depending on the social relationships it takes place in 9 , body odors were used as a means for triggering the social context and for making the social norms more salient. Our results indicate that body odors could effectively mediate moral decisions, possibly increasing the emotional experience during the decision process, and this effect is possible even when the perceiver cannot appreciate the presence of the body odors. Moreover, the current results suggest that, as Cikara et al . 10 posited, the context in which the decisions are made is relevant for understanding which decision is made.

Data Availability

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

We would like to thank Luigi Alberto Gozzi for his help in the body odors collection, Carlotta Cogoni and Michele Furlan for their input regarding the neuroimaging analysis. Financial support has been provided by the European Research Council -ERC (Grant Agreement No 682117 BiT-ERC-2015-CoG) to D.B.

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C.C., V.P. and R.I.R. developed the study concept and the study design; C.C., V.P. and E.L. collected the data; C.C., V.P. and D.B. conceptualized data analyses; C.C. performed data analyses under the supervision of D.B. and V.P., C.C and V.P. interpreted the data and drafted the manuscript. E.L., D.B., R.I.R. provided critical revisions. All authors approved the final version of manuscript submission.

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Cecchetto, C., Lancini, E., Bueti, D. et al. Body odors (even when masked) make you more emotional: behavioral and neural insights. Sci Rep 9 , 5489 (2019). https://doi.org/10.1038/s41598-019-41937-0

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Yes, Postpartum Body Odor Is Real. Here's What to Know.

Published on 3/19/2024 at 6:15 PM

It's no secret that the pregnancy and postpartum period are filled with tons of changes — physical, emotional, and mental. From pregnancy nose to postpartum depression , the symptoms can run the gamut. But one lesser-talked about consequence of bringing life into this world is postpartum body odor. Put simply: you may smell different after giving birth.

New moms on TikTok have brought about a sense of radical honesty to the symptom, admitting that postpartum B.O. can be brutal. "Why do I ALWAYS smell like an onion?" one creator captioned under a reaction video sniffing her underarms . Other parents hopped in the comments section to join in solidarity. "I'm no joke putting deodorant on 6 times a day," one person wrote. "I smelled my armpits that first time and was like 'THIS IS COMING FROM ME???!,'" another states.

While a quick glance through a comment section can reassure you that you're not alone, you may still be wondering why body odor changes postpartum — and whether you'll smell different permanently, or if things will eventually go back to normal. So we asked an MD. Here's what to know.

Postpartum Odor: Why Does It Happen?

If you smell a little stronger (or even a lot stronger) postpartum, it's not typically cause for concern. It can happen for a number of reasons, says Shieva Ghofrany, MD, ob-gyn, cofounder of Tribe Called V and advisory board member for POPSUGAR's Condition Center .

Hormonal Changes

For starters, "the drop in estrogen postpartum changes your body's thermoregulation and triggers more sweating," Dr. Ghofrany explains, adding that the same thing can happen during menopause. In other words, when estrogen and progesterone levels drop it signals to your brain that you're hot and your body starts to sweat in response, according to the Cleveland Clinic . As you sweat more, you might find that you smell more, too.

It could also be your nose and hormones playing tricks on you, though. These hormone dips, coupled with the increased sense of smell that may occur postpartum , can lead one to think they smell more than they actually do, Dr. Ghofrany says. In reality, you're just sweating more than normal and your sense of smell is heightened.

Breastfeeding

If you're breastfeeding, you've got a whole new body fluid you're getting used to: breast milk. Babies aren't known for their neatness in eating, and even if you're exclusively pumping, as your supply regulates, you may experience breast milk leakage. Milk has an odor, especially if it gets trapped near the skin (like beneath or between one's breasts), Dr. Ghofrany says. So what you may suspect is a change in your body odor may just be some spilled milk.

What's more, prolactin, the hormone that stimulates the production of milk, can also suppress estrogen levels, contributing to increased sweating, and possibly increased odor.

Lochia is the vaginal discharge that occurs after giving birth and is a mixture of blood, mucus, tissue, and uterine tissue, per the Cleveland Clinic . It's often characterized as smelling similar to a period, but others find that the odor is stronger or just different. It's been described as sour, metallic, or musty. (If you're unsure whether the odor you're smelling is normal, it's always worth checking with your doctor to make sure you don't have a UTI, BV, or other infection that could be responsible.)

Hygiene and Self-Care

The days, weeks, and months after having baby can be overwhelming. Parents are caring for a new human and a lot is required of them, meaning they may not have much time to shower. Additionally, some people may be reluctant to bathe or give themselves a thorough cleaning right after giving birth because they're still healing from labor and are afraid of hurting or even injuring themselves. So they may simply be dealing with a little more body odor than they're normally accustomed to.

How Long Does Postpartum Odor Last?

If the smell you notice is truly body odor, it's likely related to hormones. This type of postpartum B.O. won't last forever — but it may last a little longer than you'd expect. The Cleveland Clinic notes that it can begin to taper off as early as one to two months postpartum as the hormone swings behind the odor begin to even out.

But Dr. Ghofrany says people who are breastfeeding may notice their body odor smells a little different until they stop nursing , when their hormone levels return to pre-childbirth levels — and that could be any time between a few weeks to a couple years or more. Ultimately, every body is different.

If the smell is more related to lochia, postpartum bleeding typically tapers off around six weeks, and you'll notice the scent leaving with it. If it's related to lifestyle, it'll last until you get into the swing of your new routine — which, we promise, will happen eventually!

How to Manage Postpartum Odor

There's nothing "wrong" with postpartum odor changes, and there's no need to "treat" it, beyond keeping up with regular hygiene practices. But while it's fine to use soap, don't douche or put soap inside the vagina, and don't over-wash the vulva, as that can throw off the skin's pH and cause yeast infection or bacterial vaginosis . If you're concerned that the odor you're experiencing isn't normal, contact your ob-gyn to ask for their input.

When to Worry About Postpartum Odor

You can always reach out to your doctor to ask for them to weigh in on the symptoms you're experiencing, and it's better to err on the side of caution when you're postpartum — you've just been through a major health event.

But definitely consider talking to your healthcare provider if the odor you're noticing is very strong or foul, and/or accompanied by pain, fever or chills, body aches, or fatigue, as these can be signs of an infection.

Alexis Jones is the senior health editor at POPSUGAR. Her areas of expertise include women's health, mental health, racial and ethnic disparities in healthcare, diversity in wellness, and chronic conditions. Prior to joining POPSUGAR, she was the senior editor at Health magazine. Her other bylines can be found at Women's Health, Prevention, Marie Claire, and more.

• Postpartum Bodies

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'rhop' star karen huger smelled of booze after crash, cops say, 'rhop' star karen huger reeked of booze after crash ... according to cops, exclusive 132 3/22/2024 4:57 pm pt.

Karen Huger was swaying and had a strong odor of alcohol on her breath following her frightening crash Tuesday night in Potomac, MD ... this according to the police report.

According to the report, obtained by TMZ, officers noted the 'Real Housewives of Potomac' cast member also had slurred speech and bloodshot eyes when they arrived on scene -- and they say she didn't answer when cops asked her twice how much she had to drink.

Officers also noted she had 2 closed bottles of the alcoholic beverage Stella inside her vehicle.

The report adds that while cops thought Karen appeared to be intoxicated ... she declined to undergo a field sobriety test or a breathalyzer.

Fire rescue, which also responded to the scene, tried to get her to sit on a stretcher -- but the report says she refused both the stretcher and any medical care.

According to officers, Karen also made it clear she did not wish to be recorded when officers told her she was on their bodycam footage.

She was ultimately arrested for DUI, and driven to the police station where she was issued citations ... and later released to her husband, Raymond .

As we reported ... cops told us Karen hit the median and a street sign late Tuesday night while driving her 2017 Maserati -- and a security guard in the neighborhood called the police after witnessing the whole thing.

Huger hasn't addressed the charges yet.

BTW, we spoke with Karen's 'RHOP' costar Candiace Dillard Bassett ... who filled us in on the folks showing her tons of support following her crash -- as well as what it might mean for Karen's future on the series.

Pretty interesting insight from a reality bedfellow ... take a look for yourself.

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