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Shaving of axillary hair has only a transient effect on perceived body odor pleasantness

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In contrast to other apes, humans have relatively greater amounts of armpit hair, which is thought to retain signaling molecules. Although armpit shaving is widespread cross-culturally, its effect on body odor has been little investigated. In four experiments, we tested the effect of shaving and the subsequent regrowth of axillary hair. Armpit odors were collected from men who regularly shaved (group S) or who had never shaved (group N) their armpits before. The samples were subsequently rated by women for intensity, pleasantness, and attractiveness. In Experiments I, II (group N) and III, subjects firstly shaved one armpit and then let the hair regrow over 6 or 10 weeks. In Experiments I, II (group S) and IV, subjects shaved both armpits before the sampling and subsequently shaved one armpit during the same period, leaving the second armpit unshaved. Odors of the shaved armpits were rated more pleasant, attractive, and less intense compared to the unshaved armpits (Experiment I (group N)). However, no significant differences found in Experiments II and III (group N) suggest the effect of shaving is relatively minor. Moreover, there were no significant differences in odor comparing unshaved armpits with armpits after 1 week of regrowth (Experiments I, II (group N) and III) or comparing regularly shaved armpits with armpits after 1 or 3 weeks of regrowth (Experiments I, II (group S) and IV). The odor of shaved armpits was rated significantly more attractive compared to the armpits where hair had been regrowing for 6 or 10 weeks.
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ORIGINAL PAPER
Shaving of axillary hair has only a transient effect
on perceived body odor pleasantness
Dagmar Kohoutová &Anna Rubešová &Jan Havlíček
Received: 22 November 2011 / Revised: 1 December 2011 / Accepted: 5 December 2011 / Published online: 29 December 2011
#Springer-Verlag 2011
Abstract In contrast to other apes, humans have relatively
greater amounts of armpit hair, which is thought to retain
signaling molecules. Although armpit shaving is widespread
cross-culturally, its effect on body odor has been little
investigated. In four experiments, we tested the effect of
shaving and the subsequent regrowth of axillary hair. Armpit
odors were collected from men who regularly shaved
(group S) or who had never shaved (group N) their
armpits before. The samples were subsequently rated
by women for intensity, pleasantness, and attractiveness.
In Experiments I,II (group N) and III, subjects firstly
shaved one armpit and then let the hair regrow over 6
or 10 weeks. In Experiments I,II (group S) and IV,
subjects shaved both armpits before the sampling and
subsequently shaved one armpit during the same period,
leaving the second armpit unshaved. Odors of the
shaved armpits were rated more pleasant, attractive,
and less intense compared to the unshaved armpits
(Experiment I(group N)). However, no significant dif-
ferences found in Experiments II and III (group N)
suggest the effect of shaving is relatively minor. More-
over, there were no significant differences in odor
comparing unshaved armpits with armpits after 1 week
of regrowth (Experiments I,II (group N) and III)or
comparing regularly shaved armpits with armpits after 1
or 3 weeks of regrowth (Experiments I,II (group S) and
IV). The odor of shaved armpits was rated significantly
more attractive compared to the armpits where hair had
beenregrowingfor6or10weeks.
Keywords Armpit .Attractiveness Human .Olfaction .
Scent .Smell
Introduction
The last two decades have witnessed an outburst of interest
in human chemical ecology, both in the scientific literature
and the popular media. The majority of studies have focused
on genetically related traits influencing body odor, particu-
larly in mate choice and motherinfant contexts. These
include research on individuality, gender, MHC, and other
aspects intrinsic to the odor carrier (for recent reviews see
Hays 2003; Wysocki and Preti 2004; Havlicek and Roberts
2009). However, as in other species, human body odor is
also shaped by numerous environmental factors. Most non-
genetic variation can be accounted for by differences in
reproductive status, emotional state, infections, and groom-
ing habits (such as using perfumes or deodorants) (reviewed
in Havlicek and Lenochova 2008). For instance, it has been
repeatedly demonstrated that men find the body odor of
women not taking oral contraceptives most appealing when
conception is most likely (e.g. Kuukasjärvi et al. 2004;
Havlicek et al. 2006). Dietary habits may also have a pro-
found effect on body odor. Havlicek and Lenochova (2006)
recently showed that the odor of men on a red meat diet was
judged less attractive than on a meat-free diet.
Communicated by T. Bakker
D. Kohoutová :J. Havlíček (*)
Department of Anthropology, Faculty of Humanities,
Charles University,
Husníkova 2075,
155 00 Prague 5, Czech Republic
e-mail: jan.havlicek@fhs.cuni.cz
A. Rubešová
Department of Philosophy and History of Sciences,
Faculty of Science, Charles University,
Viničná 7,
128 44 Prague 2, Czech Republic
Behav Ecol Sociobiol (2012) 66:569581
DOI 10.1007/s00265-011-1305-0
The axillary region is the most intensely studied body part
regarding chemical communication. Human axillary odor has
an individual character dependent on specific microflora pres-
ent in the human armpit area (Shelley et al. 1953). Aerobic
coryneforms, propionibacteria, staphylococci, and micrococci
are the major axillary microbial organisms (Rennie et al.
1991). These microorganisms metabolise the products
of axillary glands, creating volatile odors (Rennie et
al. 1991; Gower et al. 1994;Natschetal.2003). The
axillary area has some unique features, such as, the
abundance of apocrine glands. This led some theorists
to speculate that in humans the axillary products specif-
ically evolved for communication (e.g. Comfort 1971).
The location might be especially advantageous due to
the upright posture of modern humans (Pawlowski
1999). Another specific feature is the presence of axil-
lary hair which has been proposed to serve to retain
chemical compounds active in communication processes
(Cohn 1994). This is supported by the study of Nixon
et al. (1988) who found 16-androstenes in the axillary
hair extracts. Some of these compounds, in particular
androstenol, androstenone and androstadienone, have
been shown to influence various social interactions
(Cowley and Brooksbank 1991; Jacob et al. 2002;
Lundstrom et al. 2003; Pierce et al. 2004;Saxtonet
al. 2008; for review see Havlicek et al. 2010). Other
odoriferous axillary chemicals, in particular various sat-
urated and unsaturated fatty acids, are also thought to
bind to armpit hair (Zeng et al. 1991;Natschetal.
2003,2006). Moreover, other great apes have apparently
less hair in their armpits (S Lhota personal communica-
tion) which is again suggestive of the idea that human
axillary hair could have evolved as an adaptation.
Shaving of axillary hair is a widespread practice not only
within the context of Western cultures but also in the Near
East, India and elsewhere. In Western cultures, armpit shav-
ing is regarded as a social norm in women, with the over-
whelming majority of women regularly performing it
(Tiggemann and Kenyon 1998; Tiggemann and Hodgson
2008). Recently, it is becoming popular among men as well.
However, actual figures, together with a record of the social
profile and motives of men engaged in this grooming activ-
ity, are missing. Interestingly, the effect of axillary hair
shaving on body odor hedonics has not attracted much
research attention. Until almost 60 years ago, as far as we
know, only one study had addressed this issue. It found that
removal of axillary hair in men resulted in a marked reduc-
tion or elimination of axillary odor for the next 24 h (Shelley
et al. 1953). However, the raters indicated only whether they
were able to smell any odor; their judgments on odor
hedonics or strength were not recorded. Moreover, the effect
of odor dynamics due to hair growth on subjective percep-
tion was not tested in the study.
The aim of our study was to test the effect of armpit
shaving in men and the consequential influence of axillary
hair growth on axillary odor hedonics, as rated by women.
The putative function of axillary hair is to retain armpit
chemicals and therefore we expected that armpit shaving
would decrease the intensity and increase the pleasantness
and attractiveness of the axillary odor. Simultaneously, we
expected that the odor of armpits with regrowing hair would
be rated more intense and less pleasant and attractive com-
pared to the odor of regularly shaved armpits. To test our
hypothesis, we performed four independent experiments
with male odor donors who regularly shaved their armpits
(group S in Experiments Iand II, and Experiment IV)as
well as those who had never shaved their armpits before
(group N in Experiments Iand II, and Experiment III). As
has been found repeatedly, both odor sensitivity and odor
preferences change in females across the course of the
menstrual cycle (Doty et al. 1981;Hummeletal.1991)
and are also affected by hormonal contraception (Caruso et
al. 2001; Roberts et al. 2008). Thus, our sample of odor
raters consisted of both users (Experiment II) and non-users
(Experiments I,III and IV) of hormonal contraception.
Experiments Iand II explored the effect of up to 6 weeks
of hair regrowth and Experiments III and IV continued for
an extended period of 10 weeks (see Fig. 1for a schedule of
the procedure). Different donors participated in each
experiment, and the same was true for the vast majority
of the raters (four raters who participated in Experiment
III and three raters in Experiment IV took also part in
Experiment I).
Methods
Subjects
To avoid body odor fluctuations across the menstrual cycle,
we chose only male subjects as odor donors. All of them
were students of various Prague universities, and none
reported dermatological or other diseases. Sexual orienta-
tion has previously been found to have an effect on hedonic
ratings of body odor (Martins et al. 2005; Sergeant et al.
2007). We therefore take this factor into account by asking
our odor donors: What is your sexual orientation?One
donor in Experiment III and two in Experiment IV identified
themselves as homosexual. Excluding homosexual donors
did not significantly affect the results. The donors were
awarded 1000 CZK (approximately US $55) as compensa-
tion for their time and potential inconvenience. The number
of samples used for the analyses of individual sessions and
the overall analyses varies as some of the donors did not
attend all of the sampling sessions (e.g. due to illness). We
further excluded from the analyses samples in which more
570 Behav Ecol Sociobiol (2012) 66:569581
than half of the women reported contamination by smoke or
perfume. Female students participated as raters in all experi-
ments. They were unpaid but received a 100-g chocolate bar
after each testing session. The number of raters varies
between individual sessions as some of them did not
attend all rating sessions. Table 1summarizes the num-
ber of samples and raters used and excluded from
particular analyses.
Experiment I
Eleven men (mean age, 20.7; range, 2023 years) served as
odor donors. They comprised two experimental conditions:
group N (n06) who had never shaved their armpits before
and group S (n05) who had been regularly shaving their
armpits for at least 1 year. Thirty female raters (mean age,
24.2; range, 1830 years) participated in this experiment. To
Fig. 1 Male armpit treatments across sessions. Note that the control
axilla in group N of Experiments Iand II and in Experiment III was
unshaved. In contrast, the control axilla in group S of Experiments I
and II and in Experiment IV was regularly shaved. Experiments Iand II
consisted of four sampling sessions and Experiments III and IV con-
sisted of three sampling sessions
Behav Ecol Sociobiol (2012) 66:569581 571
avoid a possible effect of menstrual cycle phase on odor
perception, we only recruited subjects using hormonal con-
traception (21 users of single-phase hormonal contraception
and nine users of another type of hormonal contraception).
Experiment II
Eleven men (mean age, 23.0; range, 2026 years) partici-
pated as odor donors. Six had never shaved their armpits
(group N), and five had been regularly shaving their armpits
for at least 1 year (group S). Twenty-five women (mean age,
23.7; range, 1932 years) participated as raters. To assess
possible effects of the menstrual cycle on odor perception,
we recruited only subjects not using hormonal contracep-
tion. All raters but one reported having a normal menstrual
cycle length (2335 days). The cycle length was estimated
according to the reported usual length of the cycle. The day
of the menstrual bleeding onset was considered to be the
first day of their cycle. The menstrual cycle data were split
into fertile (days 714) and non-fertile phases (days 16 and
days 1528) in a 28-day cycle following a simplified
protocol used by Havlicek et al. (2006). If the cycle
length was other than 28 days, the end of the fertile
phase was computed as F0L14, where Fis the last
day of the fertile phase and Lthe length of the cycle.
Numbers in the fertile phase per session were as fol-
lows: Session 1, 10 out of 25; Session 2, 6 out of 19;
Session 3, 11 out of 22; Session 4, 5 out of 18.
Experiment III
Twelve men (mean age, 21.8; range, 1928 years) who had
never shaved their armpits participated in this experiment as
odor donors. Seventeen women (mean age, 22.9; range, 19
28 years) using hormonal contraception (ten of them used
single-phase hormonal contraception) participated as raters.
Experiment IV
Eleven men (mean age, 21.9; range, 1927 years) who had
been regularly shaving their armpits for at least 1 year
before the study started participated as odor donors.
Twenty raters (mean age, 22.6; range, 1927 years)
using hormonal contraception (15 of them used single-
phase hormonal contraception) participated in this
experiment.
Table 1 Numbers of subjects and temperatures across individual sessions in Experiments IIV
Donors N (excluded) Donors S (excluded) Raters (absent) Outdoor temperature (°C) Indoor temperature (°C)
Experiment I Session 1 6 5 28 (2) 3.4 19
Session 2 5 (P) 5 29 (1) 4.4 1720
Session 3 6 4 (A) 24 (6) 15.7 2021
Session 4 6 5 21 (9) 14.5 1819
OA 5 4 19
Experiment II Session 1 5 (S) 5 25 3.8 1720
Session 2 4 (S, A) 5 19 (6) 7.4 1819
Session 3 6 5 24 (1) 15.5 2021
Session 4 6 5 18 (7) 15.1 1919.5
OA 4 5 12
Experiment III Session 1 12 17 7.2 2021
Session 2 11 (P) 13 (4) 2.1 1719
Session 3 12 15 (2) 5.5 1718
OA 11 12
Experiment IV Session 1 11 20 6.6 1820
Session 2 10 (A) 18 (2) 4.6 1619
Session 3 11 17 (3) 11.2 1819
OA
a
10 15
Donors N indicates men who had never shaved their armpits before and donors S men who regularly shaved one of their armpits across the four
experimental sessions. The capital letters in brackets indicate the reason why a particular donor was excluded from the analyses. Values in brackets
(raters column) indicate the number of raters who did not attend a particular session. Analyses of individual sessions included all non-excluded
donors and raters in each session. Temperature measurements represent the average daytime temperature during the individual sampling sessions
(Outdoor temperature) and the range of temperatures during the rating sessions (Indoor temperature)
Aabsent, Pcontaminated by perfume, Scontaminated by smoke, OA overall analyses
a
Data of subjects who took part in all sessions and adhered to all instructions were included
572 Behav Ecol Sociobiol (2012) 66:569581
Odor sampling procedure
In Experiments Iand II, odor samples were provided four
times over 6 weeks to test the effect of hair regrowth (see
below for details). Following the initial sampling session
(Session 1), the subsequent sessions took place after 1
(Session 2), 3 (Session 3) and 6 weeks (Session 4).
In Experiments III and IV, odor sampling was carried out
three times over 10 weeks. Specifically, following the initial
sampling session (Session 1), the subsequent sessions took
place after 6 (Session 2) and 10 weeks (Session 3).
In Experiments I,II (group N) and III, the effect of
shaving on formerly non-shaved armpits and the temporal
effect of hair regrowth was tested by asking each subject to
shave one of his armpits, randomly assigned by the exper-
imenter, the evening before the first odor sampling, and then
let the hair grow (see Fig. 1).
In Experiments I,II (group S) and IV, the effect of hair
growth on shaved armpit odor was tested by asking subjects to
shave both their armpits every other day for 1 week before the
sampling for Session 1. Subsequently, they shaved one armpit
every other day during the 6- or 10-week experimental period,
and the second armpit was left unshaved (see Fig. 1). The side
of armpit to regrow was again randomly assigned by the
experimenter.
Two days before each sampling session, the subjects
were provided with cotton pads, a T-shirt, a plaster, two
zip-lock plastic bags for storing the odor samples, razors
(Wilkinson Sword Extra II Sensitive), non-perfumed soap
(Sara Lee Household and Body Care, Sweden) and an
instruction sheet. The donors were instructed to refrain from
the following activities 2 days before collecting the samples
and on the day of wearing the pads: (1) using perfumes,
deodorants, antiperspirants, aftershave and shower gels; (2)
eating meals containing garlic, onion, chili, pepper, vinegar,
blue cheese, cabbage, radish, fermented milk products, mar-
inated fish; (3) drinking alcoholic beverages or using other
drugs; (4) smoking; (5) sexual activity; (6) sleeping in a bed
with a partner or pet. Whilst wearing the pads, they were
also asked to avoid intense physical activity (e.g. jogging,
playing football, etc.).
Odor samples were collected using elliptical pads approx-
imately 9× 7 cm in size madeof 100% cotton (Ebelin cosmetic
pads, DM-drogerie markt, www.dm-drogeriemarkt.cz)worn
in the armpits (cf methods in Havlicek et al. 2005,2006). In
the evening before the sampling session, the odor donors
showered without using even the non-perfumed soap. In the
morning (7 a.m.) the donors applied their cotton pads to both
armpits using 3 MMicroporesurgical tape and wore
them for 24 h. Sampling length was kept constant
across the experiments as it can affect the quality of
the samples (Havlíček et al. 2011). To avoid odor con-
tamination from the donorsclothes or from the
background, donors wore the white 100% cotton T-shirts
provided (previously washed without washing powder) as
the first layer of their clothing. The following morning they
put the pads into the two labeled zip-lock plastic bags and
handed them back to the experimenters.
The average outdoor temperatures (source: Research
Institute of Crop Production in Prague) during individ-
ual sampling sessions are shown in Table 1. However,
the actual temperatures for individual donors might vary
slightly as they spent the sampling day in various parts
of Prague.
Odor rating procedure
The experimental procedure is based on a within-subjects
design as the same group of raters assessed the odor samples
repeatedly across all sessions. Odor ratings started within an
hour after collecting all the samples to minimize the possible
influence of further bacterial activity on the samples. The
ratings took place in a quiet, ventilated room. Indoor tem-
peratures during individual sessions are shown in Table 1.
Cotton pads were placed into 500-ml opaque glass jars
labeled by a code. The testing procedure lasted from 9 a.
m. to 6 p.m. Individual raters attended each rating session
approximately at the same time of day. This procedure
minimizes a possible diurnal effect on the olfactory abilities
and temporal changes of the odors. The total sample set
consisted of 22 axillary samples (two from each donor) in
Experiments I,II and IV andof24axillarysamplesin
Experiment III. Additionally, we used two non-human
samples to control for possible fluctuations in the ratersodor
preferences. One was of floral origin, cinnamon (75% cinna-
mal, 14% eugenol and several other minor compounds) and
one of animal origin, castoreum (a musky complex compound
that originates from the beavers anal gland; we used a mixture
of 33% dipropylene glycol, 16% thujopsene, 10% gurjunene,
9% benzyl benzoate, 8% cederene and several other minor
compounds manufactured by the chemical industry). In
both cases, two drops (i.e. approximately 0.1 ml) of
100% essence (Aroma Corp. Decin) were put on a
cotton pad and was placed into a 500-ml opaque glass
jar labeled by a code, thus replicating the procedure
used with the body odor samples.
Each rater assessed all samples. The samples were divid-
ed into two equal subsets. The order of the subsets was
randomized in Session 1, and in the subsequent sessions,
the order of the subsets was the same as in Session 1. The
order of samples within a subset was randomized for each of
the sessions. The raters had a break of approximately 10 min
between assessing the two subsets to avoid sensory adaptation,
when they were offered refreshments and asked to complete a
questionnaire regarding their age, health status, menstrual
cycle and partnership status.
Behav Ecol Sociobiol (2012) 66:569581 573
Each rater washed her hands with non-perfumed soap
before the rating to avoid rating bias caused by hand
odor. They were told about the origin of the samples
(i.e. male axillary samples and the two essence sam-
ples), but they were not further informed about the aims
of the experiment.
The samples were rated on 7-point scales for their (1)
intensity, (2) pleasantness, and (3) attractiveness. Both ends
of each scale were anchored by verbal descriptions (e.g.
very unpleasant to very pleasant). For explorative purposes,
we also obtained ratings on masculinity. However, some
raters found judging this variable difficult. According to
our preliminary analyses, ratings of masculinity were in
general positively correlated with intensity ratings and
did not show any systematic trend in relation to shaving
status. For these reasons, results on masculinity are not
included here. The ratings were written down immedi-
ately after sniffing each stimulus, but the time spent by
sniffing was not restricted. Raters were also asked to
note whether they detected any contamination by smoke
or perfume.
The overall rating procedure was same across all experi-
ments. The only difference was that in Experiments III and
IV, we used a more sensitive test paradigm (the equivalent of
a forced-choice test). Within each subset, the samples were
paired. Each pair consisted of samples acquired from the left
and right armpit of a particular donor, and raters were
instructed not to use the same value within each pair (sam-
ples of one person) for any of the assessed variables (e.g.
pleasantness). This procedure is designed to detect subtle
effects as it generally strengthens the differences between
the tested groups.
Statistical analysis
The statistical package Statistica 7.1 was used for all anal-
yses. The data adhered to the requirements for parametric
tests. As our design was a within-subject one, we used a
paired ttest to test the effect of treatment within a session
and a repeated measures analysis of variance (ANOVA) to
test the dynamics of hair growth across individual sessions.
Our aim was to test possible changes in the perception of
axillary odor of shaved and unshaved armpits; therefore, we
used mean subject (raters) ratings as the unit of the analysis.
We used post hoc tests (Fisher LSD test) only when the main
effect of the ANOVA was significant. To assess any possible
effect of the menstrual cycle in Experiment II,wealso
included a binary factor (fertile/non-fertile phase, for details
on criteria see section Subjects) as an independent vari-
able within a repeated measures ANOVA. We did not use
Bonferroni adjustments for multiple tests in order not to
decrease the statistical power of our relatively small sample
sizes (Nakagawa 2004). Further, we tested specific
hypotheses concerning the effect of shaving (in contrast to
the universal null hypothesis). In such cases, adjustments
are not recommended as they inflate the chance of type II
error (Perneger 1998).
We also analysed our data with mean donor ratings as the
unit of the analysis (results are not shown). The results
showed similar trends as with raters as the unit of the
analysis, but were not statistically significant and are not
reported further. Correlations among rated variables were
computed by using Pearson correlations for each session in
all four experiments.
Results
Experiment I
In Session 1, we found a significant difference between
the odors of shaved and unshaved armpits of donor
group N. The axillary odor of shaved armpits was rated
as more pleasant (t
27
02.80; p00.009), more attractive
(t
27
02.28, p00.03) and less intense (t
27
06.55; p<0.001)
than the odor of unshaved armpits. No significant dif-
ference was found between the axillary odors from
unshaved armpits and armpits with regrowing hair in
sessions 2, 3 and 4 (all pvalues> 0.08) (Table 2). To
test the effect of axillary hair growth on odor percep-
tion, we compared the ratings from all four sessions by
a repeated measures ANOVA. The ratings of unshaved
axillae served as control. We did not find a significant effect of
armpit treatment, repeated measure or any interaction with
pleasantness (all pvalues>0.055), or attractiveness (all pval-
ues>0.11). There was a significant repeated measure effect of
intensity (F
3,36
02.70; p00.05), but no interaction with armpit
treatment. Post hoc analyses showed that the odor samples
from Session 3 were rated significantly more intense compared
to Session 1 (p00.03) and Session 2 (p00.01).
Each person from group S shaved both armpits the
day before the first sampling session. We found no
significant differences between the ratings of the left
and right shaved armpits in Session 1, nor in pleasant-
ness (all pvalues>0.07), attractiveness (all pvalues >
0.09) or intensity (all pvalues> 0.12) between repeatedly
shaved armpits and armpits with regrowing hair in the other
three sessions (Table 2). To test the effect of axillary hair
growth during all four sessions in group S, we again
performed a repeated measures ANOVA. We did not
find a significant effect of armpit treatment, repeated
measure nor any interaction with pleasantness (all p
values > 0.24), attractiveness (all pvalues>0.21) or intensity
(all pvalues>0.07).
To test possible fluctuations in the ratersodor preferen-
ces, we included two non-human samples (castoreum,
574 Behav Ecol Sociobiol (2012) 66:569581
cinnamon) in each testing session. We performed a repeated
measures ANOVA for castoreum ratings and did not find a
significant effect for any of the tested characteristics (e.g.
pleasantness) (all pvalues>0.54). For cinnamon, we found
a significant repeated measure effect for pleasantness
(F
3,18
04.10; p00.01) and attractiveness (F
3,18
04.11;
p00.005). Based on post hoc analyses in Session 1,
the cinnamon essence was rated as more pleasant (p00.05)
and more attractive (p00.008) than in Session 2. In Session 3,
it was rated as less pleasant (p00.002) and less attrac-
tive (p00.003) compared to Session 1. The cinnamon
samples from Session 4 were rated as more pleasant
(p00.02) than samples from Session 3 and less attrac-
tive (p00.002) than in Session 1. No significant
changes in ratings of intensity of the cinnamon samples
were found.
Experiment II
In Sessions 1 and 2, we found no significant difference
between the ratings of shaved and unshaved armpit odors
from donor group N (all pvalues>0.18). In Session 3, the
axillary odor of the unshaved armpits was rated as more
pleasant (t
23
02.37; p00.03) and less intense (t
23
02.95;
p00.007) than the odor of the armpits with regrowing
hair. On the contrary, in Session 4, the axillary odor of
the unshaved armpits was rated as less pleasant (t
17
0
2.76; p00.01) and more intense (t
17
08.38; p<0.001)
than the odor of the armpits with regrowing hair (Table 3).
When controlling for the ratersmenstrual cycle phase,
qualitatively identical results were obtained.
To test the effect of axillary hair growth on odor ratings,
we compared the ratings from all four sessions. Ratings of
the unshaved axillae served as a control. We did not find a
significant effect of armpit treatment, repeated measure or
any interaction with pleasantness (all pvalues > 0.31) and
attractiveness (all pvalues> 0.37). A significant repeated
measure effect (F
3,22
08.45; p<0.001) and a significant inter-
action between armpit treatment and repeated measure for
intensity (F
3,22
04.01; p00.01) was found. Based on post
hoc analyses, we found that in Session 4, the samples of
unshaved armpits were judged as significantly more intense
compared to Session 1 (p<0.001), Session 2 (p<0.001) and
Session 3 (p<0.001). The other armpit of each donor was
shaved for Session 1, and then the hair was left to regrow (i.e.
in Sessions 2, 3 and 4). Further, changes in ratings of odor
intensity were found. The samples of armpits with regrowing
axillary hair from Session 2 were rated as less intense than the
samples of the same armpits from Session 3 (p00.02) and
Session 4 (p00.008).
To test possible differences between the ratings of axil-
lary odors of the right and left armpit, each person from
group S shaved both armpits before the onset of the
Table 2 Mean (standard deviations) ratings of pleasantness, attractiveness and intensity in Experiment I
Session 1 Session 2 Session 3 Session 4
Group N U S U R U R U R
Pleasantness 3.235 (0.965) 3.532 (0.957) 3.072 (0.944) 3.190 (0.898) 3.380 (0.808) 3.331 (0.908) 3.182 (1.155) 3.233 (1.104)
Attractiveness 3.216 (0.973) 3.480 (1.046) 3.090 (0.982) 3.147 (1.005) 3.277 (0.809) 3.163 (0.908) 3.125 (1.143) 3.373 (1.040)
Intensity 4.255 (1.050) 3.589 (1.190) 4.096 (0.966) 3.864 (1.156) 3.954 (1.118) 3.913 (1.173) 3.927 (1.042) 3.811 (1.078)
Group S S S S R S R S R
Pleasantness 3.649 (0947) 3.526 (1.008) 3.647 (0.839) 3.365 (0.941) 3.250 (0.892) 3.356 (1.218) 3.528 (1.032) 3.593 (0.921)
Attractiveness 3.469 (0.983) 3.354 (0.981) 3.540 (0.775) 3.279 (1.039) 3.190 (0.907) 3.235 (1.186) 3.528 (1.016) 3.500 (0.932)
Intensity 3.630 (1.159) 3.849 (0.995) 3.523 (1.090) 3.842 (1.132) 4.298 (1.011) 4.377 (1.286) 3.590 (1.163) 3.624 (1.324)
Group N indicates donors who had never shaved their armpits before and group S donors who regularly shaved one of their armpits across the four experimental sessions. Values in bold significantly
differ at P<0.05. The ratings are based on the judges using hormonal contraception
Umean values in the unshaved armpits, Rmean values in the armpits with regrowing hair, Smean values in the shaved armpits
Behav Ecol Sociobiol (2012) 66:569581 575
experiment. First we compared ratings separately for each of
the four sessions. The only significant differences found
were that in Session 4, where the odor of the repeatedly
shaved armpits was rated as more attractive (t
17
03.07;
p00.007) than the odor of the armpits with hair regrowth.
Again when controlling for the ratersmenstrual cycle phase,
qualitatively identical results were obtained.
Subsequently, we tested the effect of axillary hair growth
during all four sessions in group S. We did not find any
significant effect of armpit treatment nor any significant
interaction between armpit treatment and repeated measure
for pleasantness, attractiveness and intensity (all pvalues >
0.35). However, there was a significant repeated measure
effect for pleasantness (F
3,22
06.33; p00.001), attractiveness
(F
3,22
08.41; p<0.001) and intensity (F
3,22
012.06; p<0.001).
Subsequent post hoc analyses showed that odor samples from
Session 2 were rated significantly less pleasant (all pvalues<
0.01), less attractive (all pvalues<0.007) and more intense (all
pvalues<0.02) compared to Sessions 1, 3 and 4,and that odor
samples from Session 4 were rated significantly more intense
compared to Session 1 (p00.002). We also performed a
repeated measures ANOVA for castoreum and cinnamon
ratings and did not find a significant effect for any of
the tested characteristics (all pvalues> 0.09).
Experiment III
We found no significant differences in ratings of pleasant-
ness, attractiveness or intensity between the odors of the
shaved (or the armpits with regrowing hair) and unshaved
armpits in any of the three sessions (all pvalues > 0.47)
(Table 4). To test the effect of axillary hair growth on odor,
we compared the ratings from all three sessions. We did not
find any significant effect of armpit treatment, repeated
measure or any interaction with any of the rated character-
istics (all pvalues>0.15).
For castoreum ratings, we found a significant repeated
measure effect for pleasantness (F
3,18
03.83; p00.04). In
Session 2, the castoreum sample was rated as less pleasant
compared to Session 1 (p00.03) and Session 3 (p00.02).
For cinnamon, we did not find a significant effect for any of
the tested characteristics (all pvalues>0.21).
Experiment IV
Each donor had regularly shaved both armpits before the
onset of the experiment. In Session 1, we found no signif-
icant difference between the axillary odors from the right
and left shaved armpits (all pvalues> 0.06) (Table 5). No
significant differences in pleasantness or intensity of the
axillary odors were found between the repeatedly shaved
armpits and armpits with regrowing hair in Sessions 2 and 3
(all pvalues>0.10). In Session 3, the odor of the repeatedly
Table 3 Mean (standard deviations) ratings of pleasantness, attractiveness and intensity in Experiment II
Session 1 Session 2 Session 3 Session 4
Group N U S U R U R U R
Pleasantness 3.359 (1.149) 3.493 (0.955) 3.434 (1.243) 3.557 (1.118) 3.490 (1.062) 3.220 (1.030) 3.198 (1.245) 3.559 (1.081)
Attractiveness 3.347 (1.057) 3.318 (1.112) 3.320 (1.263) 3.478 (1.035) 3.579 (1.054) 3.437 (1.066) 3.269 (1.292) 3.473 (1.148)
Intensity 4.008 (1.028) 4.161 (0.766) 4.070 (1.173) 3.763 (1.148) 3.955 (0.964) 4.432 (1.069) 5.261 (1.129) 4.550 (1.201)
Group S S S S R S R S R
Pleasantness 3.985 (1.045) 3.896 (1.036) 3.087 (0.963) 3.108 (1.228) 4.044 (0.999) 3.748 (1.079) 4.068 (1.235) 3.657 (1.220)
Attractiveness 3.717 (1.148) 3.694 (1.125) 3.016 (1.088) 2.855 (1.205) 3.869 (0.931) 3.693 (0.873) 3.975 (1.166) 3.381 (1.032)
Intensity 3.589 (0.869) 3.665 (0.796) 4.913 (0.906) 5.129 (905) 3.587 (0.969) 3.414 (1.061) 4.142 (1.210) 4.233 (1.170)
Group N indicates donors who had never shaved their armpits before and group S donors who regularly shaved one of their armpits across the four experimental sessions. Values in bold significantly
differ at P<0.05. The ratings are based on the judges not using hormonal contraception
Umean values in the unshaved armpits, Rmean values in the armpits with regrowing hair, Smean values in the shaved armpits
576 Behav Ecol Sociobiol (2012) 66:569581
shaved armpit was rated to be more attractive (t
16
03.13;
p00.006) than the odor of armpits with growing hair.
Subsequently, we tested the effect of axillary hair growth
during all three sessions. There was a significant repeated
measure effect for pleasantness (F
2,28
06.09; p<0.01),
attractiveness (F
2,28
04.48; p00.02) and intensity (F
2,28
0
5.58; p00.006), but no interaction with armpit treatment.
Odor samples from Session 1 were rated less pleasant com-
pared to Session 2 and Session 3. The odor samples from
Session 1 were rated less attractive compared to Session 3, and
odor samples from Session 1 and Session 2 were rated more
intense compared to Session 3. Repeated measures ANOVA
for castoreum and cinnamon ratings did not reveal any signif-
icant effect for any of the tested characteristics (all pvalues>
0.07), suggesting that there were no systematic fluctuations in
the ratersodor preferences.
Additional analyses
To explore relations between rated characteristics, we
carried out correlational analyses between individual
variablesforeachsession.Wefoundhighlysignificant
positive correlations between attractiveness and pleasantness
in all four experiments (all r00.810.92). Conversely,
negative significant correlations between intensity and attrac-
tiveness (all r00.130.57) or pleasantness (all r00.280.63)
were significant (p<0.05) in all but one case.
Some of the differences between shaved and unshaved
armpits could be attributed to the particularly intense odor of
unshaved armpits in some individuals. To check this possi-
bility, we compared the ratings of the unshaved armpits
between individual experiments. The ratings of intensity in
Experiment Icompared to other experiments were higher,
though not significantly so.
We further tested whether the proportion of raters
having previous experience with the odor studies varied
across individual experiments. The proportion of such
raters was 25%, 20%, 29% and 25% in Experiments I,
II,III and IV, respectively. This factor could potentially
explain the discrepancies between the experiments (see
Discussionfor details). However, we did not find
significant differences.
Discussion
The main aim of this study was to test whether armpit
shaving and subsequent hair growth influences the subjec-
tive perception of quality and/or intensity of axillary odor.
We used two different approaches by comparing (1) ratings
of axillary odor of one-shot shaved armpits and the
unshaved armpits of the same donors who had never shaved
their armpits before (Experiments Iand II (group N) and
Experiment III) and (2) ratings of the odor of regularly
shaved axilla and axilla with regrowing hair (Experiments
Iand II (group S) and Experiment IV). The dynamics of
odor development during hair growth was tested for 6 weeks
in Experiments Iand II, and for 10 weeks in Experiments III
and IV.
In a series of experiments, we demonstrated that axillary
hair grooming affects the perception of odor intensity, pleas-
antness and attractiveness. In general, our results show that
Table 4 Mean (standard deviation) ratings of pleasantness, attractiveness and intensity in Experiment III
Session 1 Session 2 Session 3
U SURUR
Pleasantness 3.484 (0.552) 3.419 (0.552) 3.521 (0.614) 3.591 (0.600) 3.559 (0.713) 3.594 (0.609)
Attractiveness 3.331 (0.671) 3.390 (0.519) 3.387 (0.678) 3.449 (0.595) 3.487 (0.807) 3.570 (0.558)
Intensity 4.086 (0.679) 4.066 (0.533) 3.873 (0.584) 3.868 (0.704) 3.736 (0.840) 3.658 (0.705)
No significant differences at P<0.05 were found. The ratings are based on the judges using hormonal contraception
Umean values in the unshaved armpits, Rmean values in the armpits with regrowing hair, Smean values in the shaved armpits
Table 5 Mean (standard deviations) ratings of pleasantness, attractiveness and intensity in Experiment IV
Session 1 Session 2 Session 3
SSSRSR
Pleasantness 3.162 (0.865) 3.180 (0.786) 3.403 (0.669) 3.540 (0.682) 3.580 (0.739) 3.451 (0.867)
Attractiveness 3.137 (0.873) 3.167 (0.915) 3.394 (0.800) 3.441 (0.745) 3.645 (0.803) 3.343 (0.906)
Intensity 4.472 (0.718) 4.253 (0.734) 4.501 (0.536) 4.459 (0.567) 4.084 (0.701) 4.181 (0.548)
Values in bold significantly differ at P<0.05. The ratings are based on the judges using hormonal contraception
Rmean values in the armpits with regrowing hair, Smean values in the shaved armpits
Behav Ecol Sociobiol (2012) 66:569581 577
the axillary odor of shaved armpits is rated as more pleasant,
more attractive and less intense compared to the unshaved
armpits of the same individual. However, the magnitude of the
observed effect is presumably not very high as we found
differences between the shaved and unshaved armpits only
in Experiment Ibut not in Experiments II and III.Moreover,
no differences were found between regularly shaved armpits
(group S) and armpits where hair had been regrowing for 1 or
3weeks.Onlyafter6(ExperimentII)or10(ExperimentIV)
weeks of hair regrowth were unshaved armpits judged to
smell less attractive than shaved armpits. The lack of the effect
in Experiment III and partially in Experiment IV is particularly
striking as we used the more sensitive force choice paradigm
which strengthens the differences between the tested groups.
Effect of one-shot shaving
Significant differences found in Experiment I(group N) but
not in Experiments II and III may be due to differences in
the donors odor intensity between the experiments. It is
possible that by chance the donors in Experiment Ihad
stronger axillary odors compared to the other experiments.
The higher intensity of the unshaved armpit may have resulted
in higher differences compared to the shaved armpit. Howev-
er, comparison of intensity of unshaved armpits across the
experiments brings only limited support for this claim.
The negative results in group N obtained in Experiments
II and III can be attributed to several factors. For instance,
the raters participating in a human odor study for the first
time might judge most of the samples rather negatively
which in turn may obscure the differences between odors
of shaved and unshaved axillae. This could result in lower
variability in using our 7-point scale and lead to the so-
called floor effect. Less intense and thus also more positive
(those two scales are usually negatively correlated) ratings
of previously experienced stimuli are a widely recognized
phenomenon (e.g. OConnell et al. 1994). However, the
proportion of raters having previous experience with the
odor studies did not vary between particular experiments.
The effect of one-shot shaving observed in Experiment I
was only transient. One week after shaving the axillary hair,
we did not find any significant differences compared to the
odor of the unshaved armpit. Further, no significant differ-
ences in pleasantness or intensity were found between the
axillary odors from the unshaved armpits and the armpits
with regrowing hair for a period of up to 10 weeks in
Experiments Iand III. These results are in accord with the
study of Shelley et al. (1953). They indicate that the axillary
odor is not present for 24 h after armpit shaving, but is again
perceivable after 48 h. However, the raters in the study of
Shelley et al. indicated only whether they could smell any
odor at all and did not judge its strength or pleasantness.
Moreover, from the method description, it is not clear
whether the raters could see the targets while smelling their
armpits, a factor which might have biased the results.
Effect of regular shaving
The next aim of our study was to compare the odor of a
regularly shaved armpit and the odor of an armpit with
regrowing hair (group S). To our knowledge, this effect
has not been studied previously. To avoid possible odor
instability due to changes in microbial colonization in freshly
shaved axilla we chose male donors who had been shaving
their armpits regularly for at least 1 year before the beginning
of the study.
We found no significant difference in pleasantness, attrac-
tiveness and intensity of the axillary odors between repeatedly
shaved armpits and armpits with 1 or 3 weeks of hair
regrowth. On the other hand, the odor of the repeatedly
shaved armpits was rated as more attractive than the odor of
armpits with 6 (Experiment II)or10(ExperimentIV)weeks
of hair regrowth. The results suggest that only relatively long
hair causes differences perceived by humans. Anthropomet-
rical observations state 0.91.0cm per month axillary hair
growth in Caucasian populations with minor individual and
seasonal variability (Martin and Saller 1961). Although we
did not measure hair length, we can estimate that it was about
1.5 cm after 6 or 2.5 cm after 10 weeks. Alternatively,
a longer time may be needed to re-establish different
bacterial population following long-term shaving com-
pared with one-shot shaving.
The odor quality and intensity are probably not influ-
enced only by the presence or removal of hair but also by
changes in or damage to the skin due to shaving. Regular
axillary shaving causes graver axillary skin damage than
one-shot shaving (Marti et al. 2003). The modification of
the skin surface in the armpit area may cause changes in the
composition of axillary microflora and subsequently it may
modify the intensity and/or quality of the axillary odor.
Whether such changes can be perceived by human subjects
should be addressed in future studies by employing subjects
with one regularly shaved axilla and the other shaved singly.
Moreover, in our study, we did not test the differences
between the odor ratings of the unshaved and regularly
shaved armpit. Nevertheless, as we found differences between
the ratings of the regularly shaved armpit and the armpit with
hair growing for 6 and subsequently 10 weeks and also
between the one-shot shaved axilla and unshaved axilla, we
may expect similar or greater differences between the
unshaved and regularly shaved armpits.
Effect of hair growth
The influence of hair growth dynamics on body odor was
tested by comparing the ratings across individual sessions.
578 Behav Ecol Sociobiol (2012) 66:569581
We employed the same protocol in all testing sessions to
make conditions as standard as possible. It included restric-
tions in the consumption of certain food and alcohol and in
activities, the same sampling length, ratings attended at
similar time of day and so on. However, it is important to
note that there were still a number of external factors which
could not be controlled and therefore the results of between
session analyses should be interpreted with caution. One
such intervening factor is the environmental temperature
and humidity during the sampling sessions. Temperature
positively influences intensity of perspiration and subse-
quently increases the humidity in the axillary area. Increase
in temperature and humidity results in higher growth of a
number of skin microflora (Hartmann 1983) as well as in the
rate of colonization by axillary microorganisms which
changes the intensity of axillary odor (Hopwood et al.
2005). In Experiments Iand II, there was a relatively high
increase in the environmental temperature (cca 10°C) between
sampling Sessions 2 and 3 (see Table 1). This might be the
reason why the odor samples(provided by men from group N)
in Experiment Iwere rated more intense in Session 3 com-
pared to Sessions 1 and 2. Another example of the possible
environmental temperature influences might be the ratings in
Experiment II. For instance, odor samples (provided by men
from group S) from Session 4 (outdoor temperature, 15.1°C)
were rated more intense compared to Session 1 (outdoor
temperature, 3.8°C).
Yet another factor which might have a systematic effect
on between-session comparisons is seasonal variation in
eating habits. As mentioned above, we tried to control the
diet components presumed to influence body odor. However,
the effect of the diet is still a largely unexplored field (for a
review, see Havlicek and Saxton 2009), and for instance the
amount of meat consumed, which is known to influence the
quality and intensity of body odor (Havlicek and Lenochova
2006), might have varied across the sessions. Other important
factors, which influence the results in olfactory studies, are
changes in mental condition (e.g. in mood) and subsequent
changes in the olfactory preferences of raters. Also, possible
habituation to the samples might influence the results. The
results of the longitudinal part of our study suggest that the
aforementioned factors probably had the main influence on
changes in ratings of odor samples and as already mentioned
above, the between session analyses should be interpreted
with caution.
Other confounds and implications
Some of the results may be further attributed to higher noise
caused by the fluctuations in both odor sensitivity, peaking
around ovulation and preferences across the ratersmenstrual
cycle (Doty et al. 1981;Hummeletal.1991;Grammer1993;
Pause et al. 1996). In Experiment II, where the raters did not
use hormonal contraception, we unexpectedly found that the
odor of the unshaved armpits was judged significantly more
pleasant and less intense compared to the armpits with
regrowing hair in Session 3. To check for this con-
founding factor, we included the data on menstrual
cycle phase in the analyses. However, we did not find
any effect of the cycle. Our further inspection of possi-
ble confounding factors (e.g. the donorsphysical activ-
ities) also did not reveal any potential reason for the
observed effect. In view of the negative results in Ses-
sion 1 and the surprising result of Session 3, the overall
picture in Experiment II is mixed. To increase the
sensitivity of our experiments, we recruited only women
using hormonal contraception in three other experi-
ments. In contrast to non-pill users, olfactory functions
in women taking contraceptive pills are expected to be
relatively stable (Caruso et al. 2001, although see Doty
et al. 1981 for different results). Analyses including
menstrual cycle data in raters using hormonal contra-
ception again did not affect the results (data not shown).
Another possible contributing factor might be the differ-
ences between axillary odor of the right and left armpit
caused by the differences in the local microflora. It is not
yet clear from the literature whether the left and right armpit
microflora differs (Hopwood et al. 2005) or not (Leyden et
al. 1981; Rennie et al. 1991). The side of armpit which was
shaved was assigned randomly, although it is possible that
the majority of donors shaved the stronger axilla, particu-
larly given the small sample size, and this could obscure the
results. As laterality may influence the intensity of the odor
produced in each armpit, we checked our subjectshanded-
ness, but did not find any difference among the individual
experiments. Further, the comparison of the left and right
shaved armpits (Session 1, group S in Experiments I,II and
Experiment IV) and unshaved armpits between individual
sessions in Experiments I,II and III (group N) showed its
relative stability. Contrary to expectation, we found signif-
icant fluctuations in the intensity ratings among axillary
odors of the unshaved armpits in Experiment II. However,
in general, these comparisons support the assumption of
similarity between both armpits and justify our within-
subject design. Thus, the differences we found in particular
sessions were probably not caused by distinctions between
the axillary odor of the right and left armpits. This is in
agreement with a recently published study which in general
suggests no perceptional variation between armpit sides
(Ferdenzi et al. 2009).
In our study as well as in Shelley et al. (1953), the effect
of shaving was tested only in men. We chose this approach
to avoid body odor fluctuations across the menstrual cycle
(e.g. Kuukasjärvi et al. 2004; Havlicek et al. 2006). It is
reported in most studies that adult womens body odor is
generally weaker than mens (e.g. Hold and Schleidt 1977).
Behav Ecol Sociobiol (2012) 66:569581 579
The magnitude of the observed effect of shaving is rather
small and therefore it is a matter of debate whether conducting
the same experiments with female donors would lead to
similar conclusions. As in Western cultural settings, axillary
hair removal is much more widespread in women (Tiggemann
and Kenyon 1998; Tiggemann and Hodgson 2008)itshould
be tested experimentally, too.
As a consequence of this study, we suggest that shaving
habits should be considered in human odor studies. This is a
particularly important issue in studies employing a between-
subjects design on individuals who might systematically
differ in their grooming habits. For instance, Martins et al.
(2005) tested the odor attractiveness of male and female
homosexuals compared to heterosexual men and women.
The number of individuals shaving their armpits, a habit
more widespread in women and in the gay community, was
not reported.
The differences observed between shaved armpits and
armpits with axillary hair might be in fact far greater than
our results show. Cotton pads worn by donors in their
armpits represent a mechanical barrier for the retention of
chemical compounds and therefore this treatment might
partly substitute the assumed function of axillary hair
(i.e. retention of volatile compounds). In our previous studies
(e.g. Havlicek et al. 2006), we advocated the use of armpit
pads instead of T-shirts as media for body odor collection as
with T-shirts, the source of the odor cannot be specified. It is
possible that for testing the effect of armpit hair the T-shirt
method would be more suitable. At this point this issue
remains only speculative as the validity of methods used in
human chemical ecology has scarcely been tested (for a full
discussion see, Lenochova et al. 2009).
In sum, our study shows that axillary hair shaving has an
impact on body odor quality and intensity. However, the
effect is relatively weak and was not observed in all experi-
ments and also not when the hair was relatively short. One-
shot shaving seems to have a relatively short-term effect as
the development of an odor similar to unshaved axilla in
one-shot shaved axilla was observed as early as after 1 week
of hair regrowth. On the other hand, odor development of
regularly shaved axilla after regrowth seems to be more
profound as it differed from shaved axilla after 6 weeks.
Our results are, in general, consistent with the idea that
axillary hair developed for the retention of chemicals which
may serve in chemical communication (Cohn 1994)and
contribute to our emerging understanding of the complex
nature of human chemical ecology.
Acknowledgements We wish to thank all volunteers for their partic-
ipation in the study, Jindra Havlickova, Robert Martin, Tamsin K.
Saxton and Jarka Valentova for the valuable advice and language
corrections, Pavlina Lenochova for helping with data collection and
Aroma Corp. Decin for providing samples of essences. The study was
supported by Grant Agency of Charles University (GAUK 57010),
Grant Agency of Czech Republic (GACR 406/09/0647) and Czech
Ministry of Education grant 0021620843.
Ethical standards This study complied with the current laws of the
Czech Republic.
Conflict of interest The authors declare that they have no conflict of
interest.
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... Thornhill & Gangestad [190] Singh & Bronstad [172] Kuukasjärvi et al. [95] Havlíček et al. [67] Gildersleeve et al. [59] Lobmaier et al. [106] Vaglio et al. [196] Habel et al. [ Croijmans et al. [23] Lenochová et al. [99], Allen et al. [5] Kohoutová et al. [91] Zhang et al. [208] negative bias since infancy which serves an evolutionary adaptive purpose [197]. Moreover, the odor release of fear, stress, and anxiety likely share a common physiological mechanism that manifests in the rapid activation of the fight-or-flight stress response, during which the adrenalin release stimulates the secretions from the apocrine sweat glands [32,64]. ...
... The function of axillary hair has been proposed to be retention of the chemical compounds released from the apocrine glands [20], such that hair removal was found to eliminate axillary odor up to 24 h after shaving in men [168]. Similarly, Kohoutová et al. [91] found that the odor of shaved male underarms was more attractive and pleasant and less intense than unshaved ones from the same person. However, this effect was only temporary and it was dependent on whether the donor shaved his axillary hair regularly or had never shaved them. ...
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Humans produce odorous secretions from multiple body sites according to the microbiomic profile of each area and the types of secretory glands present. Because the axilla is an active, odor-producing region that mediates social communication via the sense of smell, this article focuses on the biological mechanisms underlying the creation of axillary odor, as well as the intrinsic and extrinsic factors likely to impact the odor and determine individual differences. The list of intrinsic factors discussed includes sex, age, ethnicity, emotions, and personality, and extrinsic factors include dietary choices, diseases, climate, and hygienic habits. In addition, we also draw attention to gaps in our understanding of each factor, including, for example, topical areas such as the effect of climate on body odor variation. Fundamental challenges and emerging research opportunities are further outlined in the discussion. Finally, we suggest guidelines and best practices based on the factors reviewed herein for preparatory protocols of sweat collection, data analysis, and interpretation.
... Tribal leaders, too, are said to have a strong smell, which indicates their power not only to rise above the social order but also to inflict social disorder [47] (pp. [106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][202][203]. Finally, smell may indicate membership in a tribal group. ...
... 40). Shaving of underarm hair does reduce body odor, although the reduction disappears after a week of regrowth [116]. ...
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As hunter-gatherers, humans used their sense of smell to identify plants and animals, to find their way within a foraging area, or to distinguish each other by gender, age, kinship, or social dominance. Because women gathered while men hunted, the sexes evolved different sensitivities to plant and animal odors. They also ended up emitting different odors. Male odors served to intimidate rival males or assert dominance. With the rise of farming and sedentism, humans no longer needed their sense of smell to find elusive food sources or to orient themselves within a large area. Odors now came from a narrower range of plants and animals. Meanwhile, body odor was removed through bathing to facilitate interactions in enclosed spaces. This new phenotype became the template for the evolution of a new genotype: less sensitivity to odors of wild plants and animals, lower emissions of male odors, and a more negative response to them. Further change came with the development of fragrances to reodorize the body and the home. This new olfactory environment coevolved with the ability to represent odors in the mind, notably for storage in memory, for vicarious re-experiencing, or for sharing with other people through speech and writing.
... As body odour quality fluctuates across the menstrual cycle, we recruited only women using hormonal contraception [19,27]. All were healthy, non-smokers and regularly shaved their armpits (this can influence odour intensity: [25]). They were recruited via posters or contacted via e-mail by JF. ...
... However, our sample was large enough to detect a statistically significant increase in three measures of perceived odour quality from the restriction to restoration phase. Furthermore, our sample size is comparable to previous olfaction-related studies (e.g., [1,23,25,29]) and importantly, our within-subjects experimental design is sensitive to detect subtle changes. ...
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Previous studies on various vertebrates have shown that quantity and quality of food intake affect odour attractiveness as perceived by potential mates. In humans, the quality of body odour is similarly affected by ingested foods, such as by variation in meat and garlic intake. Nevertheless, it is not known whether quantity of food has an impact on human body odour attractiveness. Thus, here we tested how 48 h of complete caloric intake restriction affects the hedonic quality of human axillary odour. Odour samples (cotton pads fixed in both armpits and worn for 12 h) were obtained from healthy female donors across three conditions: i) during their habitual food regime; ii) after 48 h of complete caloric intake restriction (drinking water was provided), and iii) 72 h after restoration of caloric intake. Axillary samples were assessed by male raters regarding their pleasantness, attractiveness, femininity, and intensity. We also collected blood samples to assess physiological changes due to dietary restriction (e.g., glucose, sodium, albumin, and triacylglyceride assays) and anthropometric measurements at the same intervals as body odour samples. We found no differences in pleasantness, attractiveness and intensity between the odour samples collected at baseline and during complete caloric intake restriction. Interestingly, we found that body odours were rated more pleasant, more attractive and less intense after restoration of food intake as compared to the baseline and during caloric restriction. Our results suggest that restoration of food intake positively influences hedonic quality of human body odour which might thus provide cues to current fitness status and metabolic efficiency.
... Similar to most other studies investigating cyclic shifts in body odour, we provided no specific instructions on shaving axillary hair. In a previous study [65], only weak effects of axillary hair on body odour perception were found, and we are not aware of studies assessing the impact of axillary hair on the chemical body odour composition. Furthermore, we statistically controlled for odour donor ID, but the potential influence of axillary hair may not have been fully addressed. ...
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Although men’s attraction to women’s body odour has been suggested to vary over the ovulatory cycle, peaking around the fertile window, we still lack methodologically robust evidence corroborating this effect. Further, the chemical underpinnings of male preference for the odour of ovulating women remain unknown. Here, we combined perceptual and chemical analyses to investigate the axillary odour of naturally cycling women over 10 days, covering the gradual change in fertility across the ovulatory cycle with a focus on fertile days. The fertile state was confirmed by urinary ovulation tests as well as salivary oestradiol and progesterone levels. Men rated the scent of unfamiliar women, resembling a first encounter. We used multivariate analyses to relate variation in both odour ratings and chemical composition to female conception probability, temporal distance to ovulation and ovarian hormone levels. Our results provide no evidence that males prefer the odour of fertile women. Furthermore, the volatile analysis indicated no link between axillary odour composition and current fertility status. Together, our results showed no convincing support for a chemical fertility cue in women’s axillary odour, questioning the presence of olfactory fertility information that is recognizable during first encounters in modern humans.
... SD = 4.62) were recruited as body odor donors. Participation requirements were the following: good general health, non-smoking, not shaving one's armpits (Kohoutová et al., 2012), and not being vaccinated against hepatitis A/B or meningococcus in the past decade (e.g., Shepard et al., 2006). As compensation for their time and potential inconveniences, participants received 400 CZK (approx. ...
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Previous studies have shown that women perceive male faces with a more reactive immune system as more attractive, but whether body odor might likewise provide cues to immune function has not been investigated yet. These two studies tested a possible relationship between body odor quality and immunoreactivity (Study 1) and immune system function (Study 2). In Study 1, we collected body odor samples from 21 men just before and two weeks after vaccination against hepatitis A/B and meningococcus. We determined the levels of specific antibodies (selected as markers of immune system’s reactivity), testosterone, and cortisol. Subsequently, 88 female raters assessed the samples for their attractiveness, intensity, and healthiness. In Study 2, we collected body odor and blood samples from 35 men and women. We assessed key parameters of their innate and adaptive immunity, such as complement activity or total lymphocyte T and B counts and asked 95 raters to assess the samples for their attractiveness, intensity, and healthiness. In Study 1, we found no significant association between antibody levels induced by vaccination and perceived body odor attractiveness, intensity, and healthiness. We also found no significant relationship between antibody levels and steroid hormones (testosterone and cortisol). In Study 2, we likewise found no association between basal key parameters (innate and adaptive) of the immune system and body odor quality. Our results indicate that body odor does not serve as a cue to the reactivity of the immune system.
... Anecdotal observations suggest seasonal variation in axillary sweat production. Personal grooming habits including shaving of axillary hair have also been shown to affect axillary odor [42]. The cutaneous microflora of individuals is unique in terms of its diversity, composition and microbial load and the action of cutaneous microflora on constituents of axillary sweat has been shown to alter odor characteristics [43,44]. ...
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Background and objective: Luteinizing hormone-releasing hormone agonists (LHRHa) suppress gonadal hormone production and are commonly used to treat prostate cancer (PC) in men and conditions ranging from uterine fibroids to estrogen-sensitive cancers in women. They are also used to delay sexual development in children considering gender reassignment or experiencing premature puberty. As chemically castrating agents, LHRHa may affect cutaneous steroid secretions, which, in turn, could alter body odor and influence the psycho-sexual dynamics between individuals. The objectives of the present study were to determine (1) if LHRHa indeed alter cutaneous skin secretions, and (2) whether this leads to perceivable changes in body odor. Material and methods: Axillary skin secretions were collected on new cotton T-shirts worn by men undergoing androgen deprivation therapy with an LHRHa to treat PC (n = 10), both before starting the LHRHa and 3 months later. Healthy heterosexual university students (50 males, 50 females) were recruited to smell and rate the shirts for their masculinity, attractiveness, and intensity of odor. Liquid chromatography-mass spectrometry (LC-MS) was also used to analyze steroids extracted from the shirt samples. Results: LC-MS showed a statistically significant decline in the concentration of the androgenic metabolites, androsterone and 5α-androstane-3,17-dione. This confirms that LHRHa drugs that suppress gonadal hormone production markedly reduce cutaneous secretion of androgenic metabolic intermediates in adult males. However, no differences in odor were detected in the ratings of the shirts by male, female, nor male and female raters combined for any of the three variables assessed. Possible reasons why the human sniffers failed to perceive a change in odor are explored. Conclusion: Our data document that LHRHa alter steroid skin secretions in older men, but whether such changes alter the olfactory signals that might influence psychosocial interactions remains unresolved.
... Of those that did, almost all (93.1%) considered how animals avoid being infected with pathogens, cope once they are infected, or make mate choice decisions based on their potential partners' infection and immune status (Table 18.1). Only nine of the more than 25,000 papers surveyed considered the potential beneficial contributions of symbiotic microbes to animals' behavioral phenotypes or the behaviors animals engage in to facilitate the transmission of beneficial symbiotic microbes among social partners and kin [13,36,45,53,55,56,64,74,78]. Fortunately, the animal behavior research community has begun showing increasing interest in their subjects' symbiotic microbes, including the beneficial ones [5,33]. ...
Chapter
The hologenome concept of evolution posits that animals and their symbiotic microbes are emergent individuals, or holobionts, exhibiting synergistic phenotypes that are subject to evolutionary forces. Its premises are that interactions between animals and their microbes affect the fitness of holobionts, in both beneficial and deleterious ways, and that microbes and their functional genes can persist across animal host generations with fidelity. Covariance between the host genome and the microbiome can thus be maintained and holobiont phenotypes encoded by the microbiome can be subject to selection and drift within holobiont populations. Animal behavior researchers have historically underappreciated the beneficial effects of symbiotic microbes on animals’ behavioral phenotypes, but this is changing. Symbiotic microbes can protect their host animals from predators, increase their foraging efficiencies and reproductive outputs, and mediate their chemical communication systems. The objectives of this chapter are to introduce the hologenome concept of evolution and, within the framework of the concept’s premises, to present highlights of the current understanding of how symbiotic microbes contribute to animals’ behavioral phenotypes and how animals facilitate transmission of beneficial microbes to their offspring and kin. The chapter concludes with a discussion of how behavioral ecologists, in particular, are well-positioned to evaluate the explanatory value of host-microbial evolutionary models, such as the hologenome concept.
... The men had to be right-handed because, according to Ferdenzi, Schaal, and Roberts (2009), odorants collected of the left armpit of left-handed men are perceived to be more masculine and intense. They were also required to have unshaved armpits because, according to Kohoutová, Rubešová, and Havlíček (2012), women perceive the odour of shaved armpits as less pleasant, less attractive, and more intense. Thus, to ensure greater standardization, only the sweat of right-handed unshaved men was used. ...
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A growing body of literature documents how exposure to another person's fear-related body odorants can increase one's own anxiety and interfere with processing of social information, such as facial expression and impression formation. Building on these results, we aimed to 1) test the hypothesis that exposure to fear-related odorant would affect impression formation through fear contagion and 2) verify whether these effects can be observed in an ecologically valid (i.e. virtual) environment. We proposed that exposure to fear-related odorant would cause receivers to feel more anxious, which in turn would lead them to report less trust toward an unknown virtual character. This study had two distinct phases. First, we collected perspiration odorants from the armpits of 12 male senders (i.e., the source of the odorant) during the viewing of either fear or joy inducing film clips. In the second phase, 53 women receivers were exposed to either a fear, joy, or neutral odorant (i.e. between-subjects design) by breathing through a gauze attached to a disposable respirator mask while immersed in a virtual bar. As expected, receivers exposed to fear odorants felt significantly more stressed. Mediation analysis also revealed an indirect effect of exposure on trust through anxiety. More specifically, the more anxious the receiver felt, the less she trusted the virtual character. Our results show for the first time that the impact of exposure to fear-related body odorants on negative interpersonal impression formation is mediated by the anxiety induced in the receiver.
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Several previous studies have shown that in mammals, the health status of conspecifics can be assessed based on perceptual cues. Olfactory, visual, or acoustic cues may lead to avoidant behavior, thus reducing the risk of contagion by close contact with infected individuals. We tested whether immune system activation after immunization leads to perceptible changes in body odor and facial and vocal attractiveness in humans. We have experimentally activated the immune system of male participants using vaccination against hepatitis A/B and meningococcus. Their body odor, facial photographs, and vocal recordings were collected before and 14 days after vaccination. Subsequently, the body odor samples, facial photographs, and vocal recordings were assessed by female raters for their attractiveness and healthiness. We have also measured skin coloration (from facial photographs and in vivo using a spectrophotometer), vocal parameters, and C-reactive protein (CRP) levels as a marker of inflammation. We found an increase in perceived body odor attractiveness, a decrease in facial attractiveness and healthiness, and no change in vocal attractiveness 14 days after vaccination compared to the prevaccination condition. Moreover, there was no change in facial coloration or vocal parameters between the prevaccination and postvaccination conditions. Prevaccination CRP levels were negatively associated with body odor and facial attractiveness and positively associated with body odor intensity. Overall, our results suggest that perceived body odor as well as facial but not vocal attractiveness may provide cues to activation of the immune response and that each modality may carry specific information about the individual's condition.
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Body odours and their importance for human chemical communication, e.g., in the mother–child relationship, are an increasing focus of recent research. Precise examination of sampling methods considering physiology and feasibility aspects in order to obtain robust and informative odour samples is therefore necessary. Studies comparing body odour sampling at different body sites are still pending. Therefore, we sampled axilla, breast, and head odour from 28 mother–infant dyads and examined whether odour perception differs with regard to the body site. The participating mothers were asked to evaluate their own and their infant’s body odour samples, as well as odours of two unfamiliar mother–infant dyads. We tested whether maternal pleasantness and intensity evaluation, as well as recognition ability of the odours differed between the body sites. In infants, the head odour exhibited slightly lower pleasantness ratings than axilla and breast, and intensity ratings did not differ between body sites. In mothers, body site affected intensity ratings but not pleasantness ratings, as the breast odour was rated as less intense compared with head and axilla. Across all body sites, mothers rated the own and their infant’s odour as less intense when compared with unfamiliar samples. Recognition ability did not differ between body sites, and in line with previous studies, mothers were able to recognize their own and their own infant’s odour above chance. In sum, our study extends the previous methodological repertoire of body odour sampling and indicates that the axilla, breast, and head of adults as well as infants serve as informative odour sources.
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A number of studies concerning the analysis of axillary odors have assumed that the characteristic odor produced in the axillae is due to volatile steroids and isovaleric acid. Organoleptic evaluation of Chromatographic eluants from axillary extracts was employed to isolate the region in the chromatogram where the characteristic odor eluted. The odor of the dissolved eluant was eliminated when it was treated with base, suggesting that acids make up the characteristic axillary odor. Subsequent extraction of the pH-adjusted axillary extract in conjunction with organoleptic evaluation of the Chromatographic eluant, preparative gas chromatography, and analysis by GC-MS as well as GC-FTIR showed the presence of a number of C6 to C11 straight-chain, branched, and unsaturated acids as important contributors to the axillary odor. The major odor component is (E)-3-methyl-2-hexenoic acid. Three homologous series of minor components are also important odor contributors; these consist of the terminally unsaturated acids, the 2-methyl-C6 to -C10 acids and the 4-ethyl-C5 to -C11 acids. These types of acids have not been reported previously as components of the human axillary secretions and have not been proposed previously as part of the principal odor components in this area.
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The assumption that absence of oestrus and of manifestations of ovulation is specific to humans has given rise to various proposals of a role for selection pressures in the evolution of these features in the form of sexual selection or other behavioural adaptations. Analysis of the sexual behaviour of nonhuman primates and humans indicates, however, that constant receptivity is not unique to humans and that human sexual behaviour is not independent of the phases of the menstrual cycle. Quantitative differences in the distribution of sexual behaviour between humans and the nonhuman primates in question may be the result of many morphological, ecological, and cultural factors of which those differences are side effects. In the case of the postulated selection pressures on the disappearance of visual manifestations of ovulation, the rather unlikely chimpanzee model of anogenital swelling in the early Hominidae may be replaced by an early-hominoidal model in which the swelling was relatively small. Its reduction in anthropogenesis may have been caused by bipedal locomotion, the cost of water accumulation, hyperaemia of the area, and an increase in adipose tissue. Furthermore, olfactory communication in the context of sexual behaviour in the climatic conditions of the African savannah would have been sufficient for detection of the fertile periods of the menstrual cycle. Thus, assuming the existence of direct selection pressures on sexual behaviour in the Plio/Pleistocene evolution of the Homininae seems unjustified. © 1999 by The Wenner-Gren Foundation for Anthropological Research. All rights reserved.
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Individual differences in sensitivity to the putative human pheromone androstadienone were investigated in three experiments. In experiment 1, the absolute detection threshold for androstadienone was determined to be 211 micro M using the method of constant stimuli. Detection for the related compound estratetraenol was also investigated but a threshold could not be determined. In experiment 2, using an adaptive threshold test on 100 participants, the sensitivity distribution for androstadienone, but not for the reference odor phenylethyl alcohol, was bimodal, with a smaller group of individuals with a high sensitivity to androstadienone (supersmellers). A lack of correlation between thresholds for androstadienone and phenylethyl alcohol further suggested that the bimodality for androstadienone was not due to individuals with a high general olfactory sensitivity. In line with an earlier observation, there was a statistical tendency for women to be more sensitive to androstadienone than men. Results of experiment 3 preclude the possibility that the bimodal sensitivity distribution for androstadienone would depend on individual differences in trigeminal activation. Altogether, the current study suggests that olfactory sensitivity to androstadienone is bimodally distributed in the population with a subgroup consisting of highly sensitive people.
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The assumption that absence of oestrus and of manifestations of ovulation is specific to humans has given rise to various proposals of a role for selection pressures in the evolution of these features in the form of sexual selection or other behavioural adaptations. Analysis of the sexual behaviour of nonhuman primates and humans indicates, however, that constant receptivity is not unique to humans and that human sexual behaviour is not independent of the phases of the menstrual cycle. Quantitative differences in the distribution of sexual behaviour between humans and the nonhuman primates in question may be the result of many morphological, ecological, and cultural factors of which those differences are side effects. In the case of the postulated selection pressures on the disappearance of visual manifestations of ovulation, the rather unlikely chimpanzee model of anogenital swelling in the early Hominidae may be replaced by an early-hominoidal model in which the swelling was relatively small. Its reduction in anthropogenesis may have been caused by bipedal locomotion, the cost of water accumulation, hyperaemia of the area, and an increase in adipose tissue. Furthermore, olfactory communication in the context of sexual behaviour in the climatic conditions of the African savannah would have been sufficient for detection of the fertile periods of the menstrual cycle. Thus, assuming the existence of direct selection pressures on sexual behaviour in the Plio/Pleistocene evolution of the Homininae seems unjustified.
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It is a long held assumption that women have concealed ovulation, which means that men do not know when women's menstrual cycles are in their most fertile phase. Recent empirical results have provided evidence that ovulation may not be totally concealed from pair-bonded males, but the generality and the mechanisms of the finding demand further study. To examine the possible adaptive value of the phenomenon, it is necessary to study whether the ability to detect ovulation is confined to males. We studied these questions in an experiment in which male and female raters rated the sexual attractiveness and intensity of T-shirts' odors worn by 42 women using oral contraceptives (pill users) and by 39 women without oral contraceptives (nonusers). Males rated the sexual attractiveness of nonusers highest at midcycle. However, female raters showed only a nonsignificant trend for this relationship. Neither sex rated attractiveness of the odors of pill users according to their menstrual cycle. The results indicate that men can use olfactory cues to distinguish between ovulating and nonovulating women. Furthermore, the contrasting results between pill users and nonusers may indicate that oral contraceptives demolish the cyclic attractiveness of odors. Together, these findings give more basis for the study of the role of odors in human sexual behavior. Copyright 2004.
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AS FAR back as history records, man has been aware of a distinctively malodorous scent that may emanate from his axilla. Since the axilla is remarkable anatomically for the presence of the apocrine gland, the unique body odor of this area has been popularly ascribed to this structure. Furthermore, racial differences in body odor have been related to differences in number of apocrine glands seen in the various races.1 The intense acridity of body odor sometimes noted under stress situations is thought to be the result of apocrine sweating. As a result of these speculations the apocrine gland has been thought of as a "scent gland," responding to emotional stimuli and thus performing the function of such similar glands in the lower mammalia. In studying the physiology of the apocrine gland2 we have been impressed by the lack of appreciable odor in pure apocrine sweat as it
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Olfactory cues play a prominent, yet underestimated role in shaping emotional attitudes towards conspecifics. Among humans olfactory cues can have effects on behavior. In a rating study (n = 290) females rated the smell of androstenone. The emotional reaction to androstenone changed during the menstrual cycle. Females rated the main component of male body odor unattractive. This changed to a neutral emotional response at the conceptive optimum around ovulation. The finding has direct consequences for hypotheses concerning the evolutionary loss of estrus. It is suggested that the cyclic-dependent emotional rating of androstenone may facilitate active female choice of sex partners and may be a proximate cue for female mate-choice.
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This study aimed to investigate the frequency andmeaning of the removal of body hair in women.Participants were 129 female university students (meanage = 22.3 years) and 137 female high school students (mean age = 14.3 years). Almost all (>95%)were Caucasian. It was found that, as predicted, the vastmajority (92%) of women remove their leg and/or underarmhair, most frequently by shaving. This was irrespective of their feminist beliefs, but wasnegatively related to self-esteem in university students.The reasons cited for hair removal were primarilyconcerned with a desire for femininity andattractiveness. However, the reasons provided for starting toremove body hair differed between the groups, in thatthey were relatively more normative for the universitystudents than for the high school students. It was concluded that women's stated reasons forstarting the practice of hair removal reflectprimarilytheir vantage point as an observer. In fact, removingbody hair is a practice so normative as to go mostly unremarked, but one which contributessubstantially to the notion that womens' bodies areunacceptable as they are.
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The axillary microflora of 229 subjects was characterized quantitatively and the results correlated with whether the odor was pungent body odor or instead a faint “acid odor.” The axillary flora was found to be a stable mixture of Micrococcaceac, aerobic diphtheroids and Propionibacteria. Significantly higher numbers of bacteria were recovered from the axillae of those with pungent axillary odor than in those with acid odor. Aerobic diphtheroids in high numbers were recovered in all subjects having typical body odor. These included lipophilic as well as large-colony diphtheroids. When droplets of apocrine sweat placed on the forearm were inoculated with various bacteria which reside in the axilla, only diphtheroids generated typical body odor. Cocci produced a sweaty odor attributable to isovalerie acid.