1. No category

Department of Clinical Neuroscience
Undergraduate program in Psychology, 6th semester
Bachelor thesis in psychology (2PS013), 15 hp
Spring semester 2011
Human Body Odor from a
Biopsychosocial Approach
A Research Synthesis
Katarina Johansson & Nathalie Thomé
Supervisor: Professor Mats J. Olsson, Department of Clinical Neuroscience
Examiner: Professor Petter Gustavsson, Department of Clinical Neuroscience
Department of Clinical Neuroscience
Undergraduate program in Psychology, 6th semester
Bachelor thesis in psychology (2PS013), 15 hp
Spring semester 2011
Human Body Odor from a Biopsychosocial Approach
A Research Synthesis
Abstract/ Sammanfattning
Research from the past five years was reviewed and summarized by identifying reoccurring
features of human body odor. These features were then organized according to a
biopsychosocial approach. The research synthesis was conducted following a seven-step
approach. A database search for articles was made with the search words “human body
odor/odour”. A thorough screening was made resulting in 23 articles being included in the
analysis. The literature was reviewed and resulted in 11 features described with 11 keywords.
These features were then analyzed and interpreted and placed in a biopsychosocial model. By
doing so we were able to visually illustrate the multifaceted nature of human body odor. This
biopsychosocial model for human body odor provides an innovative way of looking at the
research findings and can facilitate as well as inspire future research within the field.
Keywords: Biopsychosocial model, human body odor, research synthesis
Forskning från de senaste fem åren granskades för att identifiera återkommande faktorer som
berör mänsklig kroppslukt. Dessa faktorer organiserades sedan enligt en biopsykosocial
modell. En systematisk litteraturstudie som följde en sjustegsmodell genomfördes. En sökning
för artiklar utfördes på databaser med sökorden ”human body odor/odour”. En noggrann
granskning gjordes vilket resulterade i de 23 artiklar som inkluderades i analysen. En
genomgång av litteraturen resulterade i 11 faktorer som tilldelades 11 nyckelord. Faktorerna
analyserades och tilldelades positioner i den biopsykosociala modellen, och genom att göra
detta kunde vi visuellt illustrera hur mångfacetterad kroppslukt är. Den biopsykosociala
modellen för kroppslukt är ett innovativt sätt att se på forskningsresultat och kan utöver det
bidra till framtida forskning genom att förenkla och inspirera.
Nyckelord: Biopsykosocial modell, mänsklig kroppslukt, systematisk litteraturstudie
2
Human Body Odor from a Biopsychosocial Approach
A Research Synthesis
Katarina Johansson & Nathalie Thomé
Background
This research synthesis reviews literature on the subject of human body odor with the
intention of gaining a better understanding of the field. The aim is to review the literature and
summarize the research findings in a structured way by identifying and presenting features of
human body odor treated in recent research. Furthermore, these features will be organized and
presented using a biopsychosocial model (Myers, 2006), giving a more integrated view of the
studied field.
We begin by defining human body odor. Human body odor can be referred to as two
components; the actual substance, i.e. the odorant, as well as the percept, i.e. the odor. The
human body odorant consists of a physical component and that is a fluid consisting mostly of
water, which is excreted from sudoriferous glands, more commonly referred to as sweat from
the sweat glands. Sweat is involved in regulating body temperature. Interestingly, sweat itself
is seemingly odorless; it is bacteria on the body surface that multiplies rapidly when
combined with sweat that produces an odor (Wikipedia, 2011a).
Then there is the perceptual component of human body odor. Does an odor exist
without it being captured in an olfactory sensory system and then processed on a neural level?
This may be a philosophic question without an actual answer; nevertheless in this review we
do feel that it is important to mention the perceptual component. Olfactory perception is more
than simple molecular odorant feature detection. Olfactory perception has mechanisms for
and is characterized by synthetic nature and object-oriented processes, capacity for perceptual
constancy and scene analysis as well as modulation by expectancy, attention and experience
(Wilson & Stevenson, 2006).
Besides being a physiological necessity, i.e. controlling body temperature through
sweating, researchers have found scientific proof pointing towards the existence of some kind
of human body odor communication. Communication is defined as the activity of conveying
meaningful information between a sender and an intended recipient, although the receiver
need not be present or aware of the sender's intent to communicate at the time of
communication (Wikipedia, 2011b). If human body odor communicates meaningful
information, what information is conveyed? Furthermore, does this information have any
consequences for the recipient?
Human beings function daily in social systems, and are also beings composed of
systems, like the nervous system and organs. Biological influences, such as genetic
predispositions and natural selection, psychological influence, such as cognition and emotion,
as well as socio-cultural influences, like social expectations and group influences are all
important aspects to consider when studying any human process (Myers, 2006). The
biopsychosocial model has the potential to organize our knowledge in a new and more
integrated way because it takes into account not only biological aspects, but makes us look at
the social and psychological aspects of human processes. We will therefore use the
biopsychological model as a framework to understand and organize the information gathered
from research in the field of human body odor, thus shedding new light on the field of human
body odor.
3
Aim
This research synthesis will review the research conducted during the past five years
and summarize it by identifying reoccurring features of human body odor in the literature.
These features will be assigned a keyword and organized into a biopsychosocial model
illustrating human body odor in an innovative way.
Method
According to the Karolinska Institutes rules and guidelines for research projects,
students do not have to apply for an ethical approval if the research does not include an
analysis of private information of a personal nature, or based on previous research which
includes physical alteration of participants (surgery or otherwise) or biological material
extracted from a participant which can be traced back to the participant in question. Therefore
this literature analysis did not need a formal ethical approval, however, in keeping with the
overall guidelines of the Karolinska Institute, we strived for the truth and did not include
studies that were unjust, irrelevant or of inferior quality (Styrelsen för Utbildnings etikgrupp,
2004).
We chose to conduct a literature review. A research synthesis is a type of literature
review that makes overall conclusions from past research and then presents the state of
knowledge concerning the relations of interest, and by doing so highlights important issues
that have not yet been investigated (Cooper, 2010). For this, past research was reviewed
resulting in features analyzed through all biopsychosocial levels, in order to present new
relations of interest. According to Cooper (2010), a research synthesis can be carried out by
following 7 recommended steps: (1) formulating the problem, (2) searching the literature, (3)
gathering information from studies, (4) evaluating the quality of studies, (5) analyzing and
integrating the outcomes of studies, (6) interpreting the results and (7) presenting the results.
We chose to follow this framework, and our presentation of methodology was structured
accordingly.
Step 1: Formulating the problem
The variables of interest needed to be given clear definitions and by doing so limiting
the literature search to include exclusively the literature intended. A conceptual definition
describes qualities of the variables that are independent of time and space and that describe
what is relevant to the study. In addition to this a structured definition also illustrates exactly
what the research synthesis will result in, to be more precise; describing the literature,
investigating a relationship between variables or if a relationship is associational or causal
(Cooper, 2010). Two questions were formulated in this research synthesis, the first question
drawing overall conclusions from past research and the second question proposing how the
state of knowledge could be understood from a new point of view, i.e. through the
biopsychosocial model. The following questions were formulated; (1) what features of human
body odor have been relevant in the research during the past five years? (2) How can these
features be presented in a biopsychosocial model?
Step 2: Searching the literature
Specific inclusion criteria were set beforehand in order to ensure an unbiased and
reliable application of criteria as well as retrieval of information from the study reports. For
articles to be included in our study they had to investigate or summarize human body odor
and its biological, psychological or social implications on human beings of good health, i.e.
4
without disease or condition that could affect ability to smell or produce body odor.
Moreover, these human beings had to be of fertile age, and the studies had to be documented
in literature written in English. Our broad inquiry question led to the inclusion of a wide range
of study designs as well as studies of quantitative nature as well as review articles. This
consequently resulted in a wide range of outcomes.
The following procedures were used for finding relevant literature. No specific
restrictions were made in the databases, and therefore all fields were included when the
articles were identified by the searches. The databases used were PubMed, Web of Science
and PsycINFO. These three databases were used as they were of the right disciplinary scope.
The search was restricted to articles published in the last 5 years (from 2006-03-15 to 201103-15). The search terms “body odour/odor” were used and the search was restricted to
studies about humans. This was done by selecting the option to only include studies on
humans in “limits” or by combining the search terms with the term “human”. This initial
search yielded a total of 41 hits in PubMed, 63 hits in Web of Science and 22 hits in
PsycINFO. Only articles published in English were included (see Table 2 in Appendix).
We proceeded by doing an initial screening of the 126 articles found, including
duplicates. We removed all articles not meeting our inclusion criteria. We therefore excluded
articles on physically or mentally ill populations as our previously mentioned inclusion
criteria specified that we wanted to investigate the importance of human body odor on healthy
humans. For example, all articles having studied the disorders trimethylaminuria and
isovaleric acidemia, known for causing the affected person to produce distinctive body odors,
were excluded. We also excluded studies about patients having odor hallucinations or any
other odor related disorder. Furthermore, we excluded studies that showed effect on body
odor due to exposure to abnormal levels of chemicals. Moreover, we excluded articles that
included other species than humans, i.e. studies of the malaria mosquitoes and its preferences
to particular types of body odor as well as articles of a strictly chemical nature. All duplicates
were also removed. This initial screening led to a reduction from 126 to 32 remaining articles
to be further evaluated to be included in the final analysis. Finally 23 articles remained which
were included in this synthesis.
Step 3: Gathering information from studies
In order to identify what features research within the field had focused on, each study
had to be read and summarized in a systematic way (Cooper, 2010). The summaries include
the following components; “title and publishing year”, “author”, “method design”, “results”
as well as “quality score”. This topic is further clarified in the next step (4) “Evaluating the
quality of studies”. Before starting this literature selection, a so-called “coder training” took
place in order for both authors to collect data in the same manner, in order to minimize
variation in data. The coder training consisted of a test trial where both authors separately
summarized the same article and then compared notes in order to settle on which aspects were
important to include and how these aspects should be documented.
Step 4: Evaluating the quality of studies
In order to evaluate the quality of studies, a systematic control based on assessment
criteria was introduced (Carlsson & Eiman, 2003). At this stage an initial screening of each
study had taken place, as well as a summary of each study (see Tables 5 & 6 in Appendix).
The following control consisted of two different assessment models, one for quantitative
studies as well as one for literature reviews (see Tables 3 & 4 in Appendix). By using
assessment models, studies are divided into three different quality levels. Level I is when 80100% of the assessment criteria is achieved. Level II is when 70-79 % is achieved and level
III is when is when only 60-69% is achieved making it the weakest quality level. The
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percentage for each study is calculated by dividing the points a study attained in the
assessment model used, with the total amount of points possible to attain in that model (46
points for quantitative studies and 42 points for literature reviews. Consequently, studies of a
higher assessed quality played a more important part in the final analysis and summary of
research.
Step 5: Analyzing and integrating the outcome of studies
Two questions were formulated in this research synthesis, the first question being; (1)
what features of human body have been studied in the research during the past five years?
In order to answer this first question, we started by distinguishing key features of interest, as
recommended by Cooper (2010). A summarizing keyword was assigned to each distinct
feature. An article could have one or more keywords assigned to it (see Tables 5 & 6 in
Appendix). Eleven features were found and their assigned keywords were the following:
affection, attractiveness, contraception, culture, diet, menstrual cycle, gene, major
histocompatibility complex (MHC), neuronal processing, perception and steroid hormones.
Some keywords are closely related to each other but treat different facets of a subject. The
distinction between the keywords is therefore clarified in Table 1.
Table 1. The following is a summary as well as definitions of the 11 identified features of
human body odor.
Keyword
Affection
Definition
Affection is a "disposition or rare state of mind or body" that is often associated with
a feeling (Wikipedia, 2011c).
Attractiveness Attractiveness refers to a quality that causes an interest or desire in something or
someone (Wikipedia, 2011d).
Contraception Hormonal contraception refers to birth control methods that act on the endocrine
system. Almost all methods are composed of steroid hormones (Wikipedia, 2011e).
The set of shared attitudes, values, goals, and practices that characterizes an
Culture
institution, organization or group (Wikipedia, 2011f).
In nutrition, diet is the sum of food consumed by a person or other organism
Diet
(Wikipedia, 2011g).
A gene is a unit of heredity in a living organism. It is a name given to some stretches
Gene
of DNA and RNA that code for a type of protein or for an RNA chain that has a
function in the organism (Wikipedia, 2011h).
The menstrual cycle is the scientific term for the physiological changes that can
Menstrual
occur in fertile female humans and apes. The menstrual cycle, under the control of
cycle
the endocrine system, is necessary for reproduction. It is commonly divided into
three phases: the follicular phase, ovulation, and the luteal phase (Wikipedia, 2011i).
The major histocompatibility complex is a large genomic region or gene family
MHC
found in most vertebrates that encodes MHC molecules. MHC molecules play an
important role in the immune system and autoimmunity (Wikipedia, 2011j). In some
articles, the term “human leukocyte antigen” (HLA) is used.
How the brain processes information (Wikipedia, 2011k).
Neuronal
processing
Perception is the process by which an organism attains awareness or understanding
Perception
of its environment by organizing and interpreting sensory information. All
perception involves signals in the nervous system, which in turn result from physical
stimulation of the sense organs. Perception is not the passive receipt of these signals,
but can be shaped by learning, memory and expectation (Wikipedia, 2011l).
A steroid hormone is a steroid that acts as a hormone. Steroid hormones help control
Steroid
for example the development of sexual characteristics (Wikipedia, 2011m).
hormones
6
The next step was to organizing the features through the biopsychosocial model (Figure
1). Three separate levels of analysis (the biological, psychological and social), three levels
comprised of two integrated levels (biopsychological, psychosocial and sociobiological) and
one level of analysis integrating all three levels of analysis (biopsychosocial) were used as
illustrated in Figure 1. It is important to note that the information gathered is synthesisgenerated evidence which cannot make statements concerning causality, it is used to organize
evidence from past research through a new point of view, thus aspiring to generate a better
understanding of the topic studied (Cooper, 2010).
BIOLOGY
BIOPSYCHO
SOCIOBIOLOGICAL
BIOPSYCHO
SOCIAL
PSYCHOLOGICAL
SOCIAL
PSYCHO
SOCIAL
Figure 1. The following biopsychosocial model was used as an intermediate construct through
which we organized the features of human body odor.
Step 6: Interpreting the results
The following interpretation is how we propose the features to be organized.
The biological level of analysis
Studies about body odor from a biological level of analysis have reported findings on
body odor and the menstrual cycle. The menstrual cycle is commonly divided into three
phases: the follicular phase during which follicles in the ovary mature, ovulation which is the
process in a female's menstrual cycle by which a mature ovarian follicle ruptures and
discharges an ovum and the luteal phase which begins with the formation of the corpus
luteum and ends in either pregnancy or luteolysis (Wikipedia, 2011i). In a level I quality
study, men were found to potentially use smell to monitor the menstruale phase of a
prospective partner. The authors argue that the fertile period is non-advertized in humans, but
not concealed. During the fertile phase of the menstrual cycle the body odor was rated as less
intense and more attractive than in the non-fertile phases. Significant changes across the
menstrual cycle were found in rated intensity, pleasantness and attractiveness but not for rated
feminity. Olfactory cues, sampled from women near or far from ovulation, signaling women’s
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levels of reproductive fertility, were associated with specific endocrinological responses in
men (Miller & Maner, 2010). Men were found to be more attracted to women during estrus,
e.g. in their fertile phase in their menstrual cycle (Gangestad & Thornhill, 2008). A review
article also supports the existence of olfactory cues to ovulation in humans. This study
suggests that men, for monitoring their current or potential partner’s fertility, could use such
cues. In the same review, a study showed that male subjects rated the smell of the axillae
sweat sample of women as least attractive during menstrual bleeding and most attractive
during the fertile period of the cycle. These authors argue that cyclic odor cues are a
byproduct of physiological changes rather than a specific signal of ovulation (Havlicek &
Lenochova, 2008). Men were also found to potentially use smell to monitor the menstrual
phase a prospective mate is in. Therefore, the fertile period in human females can be seen as
non-advertised, but not either concealed. During the fertile phase of the menstrual cycle, the
follicular phase, the body odor was rated as less intense and more attractive than in the nonfertile phases. It should be noted, however, that men cannot determine ovulation with
exactitude but seem to be able to do so in a probabilistic manner (Havlicek, Dvorakova,
Bartos & Flegr, 2006).
Some studies have attempted to investigate how our genetic composition affect our body
odor. For this, volatile compounds found in axillae sweat were analyzed. These volatile
compounds showed 373 peaks consistent over time. Among these candidate compounds the
chemical structures of 44 individual and 12 gender-specific volatile compounds were found.
These individual compounds provide candidates for major histocompatibility complex and
other genetically determined odors (Penn et al., 2007). The body odor of monozygotic human
twins showed that body odor is dependent on strong genetic contributions but is also subject
to a day to day variation (Kuhn & Natsch, 2009). A review study on human body odor
individuality (Lenochova & Havlicek, 2008) posits that humans do produce temporarily
stable, genetically mediated odor signatures. The significance of genetic control on body odor
individuality has been shown in studies of twins living apart, thus not sharing common
environmental factors.
An additional biological feature that research has been focusing on is the major
histocompatibility complex (MHC)’s importance for body odor preferences. In humans, the
role of MHC in body odor preferences and mate choice is controversial (Chaix, Cao, &
Donnelly, 2008). MHC genes make molecules that enable the immune system to recognize
invaders; in general, the more diverse the MHC genes of the parents the stronger the immune
system of the offspring. The role of mate choice depending on MHC-similarity has been
investigated in several studies. In Roberts and Roiser’s (2010) review study, they analyzed the
findings of studies investigating olfactory preference in humans. Two studies found no
significant difference in ratings between odors of MHC-dissimilar and MHC-similar men
among women during the follicular cycle phase. However, in another study single women
were found to prefer odors of MHC-similar men, while women in relationships preferred
odors of MHC-dissimilar men. The same results was shown by Roberts, Gosling, Carter and
Petrie (2008) in their high quality study (quality level I). Olfaction and visual channels are
suggested to act as complementary systems to achieve an optimal level of MHC in offspring;
visually humans tend to search for similar MHC, whilst olfaction indicates the favouring of
MHC dissimilar mates (Havlicek & Roberts, 2009). In a quality I study, genome-wide
genotype data and MHC types in African and European American couples were used to test
whether humans tend to, hypothetically mediated by body odor, choose MHC-dissimilar
mates. Humans were shown to possibly rely on biological factors in addition to social factors,
when choosing a mate. European Americans spouses showed significantly more MHC
dissimilarities compared with genome and African American random pairs. African American
8
spouses showed no similarities or dissimilarities across the MHC region (loci) in comparison
to genome and other random pairs (Chaix, et al., 2008).
Steroid hormones in men have also been studied, both how they affect other
individuals and vice versa. Two studies showed that men exposed to the odor of an ovulating
woman displayed higher levels of testosterone than did men exposed to the odor of a
nonovulating woman or a control scent (Miller & Maner, 2010; Rantala, Eriksson, Vainikka
& Kortet, 2006). A study conducted on homosexual and heterosexual men showed that
homosexual men displayed significantly higher olfactory sensitivity to the odor of
androstenone, which is a steroid found in both male and female sweat and urine (Wikipedia,
2011n). The authors of the study argue that sexual orientation had a significant impact on
perception of androstene, though not necessarily on a conscious level (Lubke, Schablitzky, &
Pause, 2009).
The psychological level of analysis
Moving on to the psychological level of analysis, we identified research findings about
how body odor affects and is affected by affective states. Men's self-rated confidence and
women’s judgements of the men’s visual attractiveness were found to be significantly altered
depending on whether the men where using a fragranced deodorant containing antimicrobial
ingredients and fragrance oil or a placebo deodorant. The men that were assigned the placebo
deodorant, without intimicrobial ingredients and fragranced oil, rated themselves as having
lower self-confidence and women rated the placebo-using men as being less attractive than
the men using the fragranced deodorant (Roberts et al., 2009). Mental states were also found
to induce changes in body odor. In a review authored by Havlicek and Lenochova (2008),
they mentioned a study about how watching excerpt from different movies influence body
odor. In this study, participants watched excerpts from either a comedy or a fearful movie. It
was found that “fearful body odor” was rated as less pleasant and more intense. They also
found that women were able to correctly identify “happy odor” collected from both sexes and
“fearful odor” from men but not from women. Men correctly identified “happy odor”
collected from women and “fearful odor” from men. This review also suggests that at least
some mental states may result in changes in body odor but that more research needs to be
conducted using either hedonic ratings or more objective physiological measures such as
changes in skin conductance, heart beat or hormonal levels as emotional information is not
necessarily perceived under full conscious control (Havlicek & Lenochova, 2008).
The social level of analysis
From a social level of anlysis, we identified cultural differences in preferences and diet
as important features. A study by Havelicek et al. (2008) showed that culture modulates body
odor ratings. In the United States the women seemed to be more visually oriented overall,
compared to Czeck women, whereas Czeck women tended to rate a strong male body odor
more positively than women from the United States. The consumption of red meat has shown
to have a negative impact on body odor pleasantness. The body odors of participants
following a non-meat diet was found to be significantly more attractive, more pleasant and
less intense (Havlicek & Lenochova, 2006). Havlicek and Lenochova (2008) further reviewed
articles about dietary effects on body odor. They discussed that research on human body odor
mention diet as the most significant source of environmental variability. This is way
researchers try to control the diet of their odor donors in most odor studies. In particular,
consumption of garlic, onion, chilies, pepper, vinegar, blue cheese, cabbage, radish, fermented
milk products and marinated fish are recommended to be avoided. Concerning dietary effects
in mate choice, the authors suggest that outbreeding avoidance may to some extent rely on
unattractiveness of highly unfamiliar odors. This may result, for instance, from interactions
9
between the odor of genetically distant individuals and odors due to different eating habits of
such individuals.
The biopsychological level of analysis
In the biopsychological level of analysis we identified research papers focusing on the
neuronal processing of human body odor. In a quality I study conducted by Lundström,
Boyle, Zatorre and Jones-Gotman (2009) an initial behavioral experiment demonstrated that
accurate identification of kin is performed with a low conscious recognition, indicated by low
confidence ratings. Participants were able to correctly identify their sister’s and their friend’s
body odor above chance values when compared with the body odors of strangers even though
many subjects expressed frustration with the seemingly impossible task. The same study also
showed that olfactory based kin recognition in women recruited the frontal-temporal junction,
the insula, and the dorsomedial prefrontal cortex, an area implicated in the coding of selfreferent processing and kin recognition. The neuronal response was seemingly found to be
independent of conscious identification of the individual source, suggesting that humans have
a nonconscious odor based kin detection system. In an other study by Lundström, Boyle,
Zatorre and Jones-Gotman (2008) body odors were found to be processed by a network that
was distinctly separate from common odors, indicating a separation in the processing of odors
based on their source. Smelling a friend’s body odor activated regions previously seen for
familiar stimuli, whereas smelling a stranger activated amygdala and insular regions akin to
what has previously been demonstrated for fearful stimuli. A review of behavioral studies
using body odors as stimuli suggested that the complex mixture constituting human body
odors is processed in a unique way due to its behavioral relevance. The studies regarding the
neuronal processing of human body odor processing suggests that human body odor is
processed with a low level of conscious recognition, recruiting a network distinctly separate
from the neuronal network for processing common odors (Lundström & Olsson, 2010).
The sociobiological level of analysis
A sociobiological feature is contraception. The contraceptive methods our studies have
been referring to is the birth-control pill, which is a birth control method that includes a
combination of different hormones that inhibits female fertility. We argue that the actual
choice to use contraception is dependent of social factors such as what country one lives in, a
person’s marital status or religious beliefs but the implications are of a biological nature
radically affecting women’s hormonal system. As hormonal contraception interferes with the
normal hormonal changes with the aim of preventing reproduction, the menstrual cycle was
often also studied as both features are per se intertwined. A study of high quality (quality
score I) found a significant preference shift towards MHC-similarity associated with pill use,
which was not evident in the control group. If odor plays a role in human mate choice, the
results suggest that contraceptive pill use could disrupt disassortative mate preferences
(Roberts, et al, 2008). Fertile women, e.g. not using birth control, were found to be better than
infertile women in assessing male attractiveness only by olfaction (Foster, 2008).
The psychosocial level of analysis
Several papers focused on person perception by way of body odor. The capability of
self, gender, kin and non-kin odor recognition plays a role in social interactions. We argue
that perception is psychosocial event mediating information from the external world to the
perceiving individual. In one study, family members were asked to rate the body odor of other
family members and unfamiliar individuals. The following was rated: pleasantness, intensity,
masculinity and recognition. The study found that participants showed no aversion for the
body odors of family members of the opposite sex and reduced aversion for body odor of the
10
parent of same sex as oneself compared to ratings made by unfamiliar individuals (Ferdenzi,
Schaal, & Roberts, 2010). In a review study on human body odor individuality researchers
posits that humans possess the ability to recognise, discriminate and identify other people
through the sense of smell (Lenochova & Havlicek, 2008). Research results from a quality I
study indicated that romantic love seems to affect perceptual attention in that individuals in a
state of romantic love demonstrate reduced attention to alternative partners at an early and
more automated stage of visual perception than do controls. Attention, which in involved in
the perceptive process, is the cognitive process of selectively concentrating on one aspect of
the environment while ignoring other things. Attention has also been referred to as the
allocation of processing resources (Wikipedia, 2011o). Romantic love deflects attention away
from potential new partners supporting the deflection theory leading to a reduction in
relationship threats and help maintaining the long-term commitment to one's current partner
(Lundström & Jones-Gotman, 2009). Women were also found to rely more on olfactory cues
and men more on visual cues both in partner choice and during sexual arousal (Havlicek et al.,
2008).
The biopsychosocial level of analysis
The final level of analysis is the biopsychosocial level of analysis, which leads us to our
final feature: attractiveness. We argue that attractiveness belongs in the biopsychosocial level
of analysis as biological, psychological and social aspects modulate it as judgment of
attractiveness of physical traits is partly universal to all human cultures, partly dependent on
culture, societal factors or time period, partly biological, and partly a matter of individual
subjectivity. Body odor is a quality that can attract, i.e. cause interest or desire, or evoke
disgust and avoidance. Olfactory cues has shown to modulate facial attractiveness. Male faces
were rated as significantly less attractive when combined with unpleasant odors. There were
no significant varitations between type of odors, which implies that it didn't matter if the
smells were relevant to the faces, such as body odor and male fragrance, or not, such as
rubber (Dematte, Osterbauer, & Spence, 2007). One study had men’s body odor and physical
attractiveness assessed either independently (body odor and then photography) or together
(body odor and photography at the same time) by women. The independent assessment of
attractiveness, by looking at a picture of a man and then smelling the body odor separately,
gave a better prediction of the "overall attractiveness" than the assessments made by looking
at both picture and smelling the body odor at the same time. This was the same for all women,
although fertile women were better at assessing attractiveness only by olfaction (Foster,
2008).
Step 7: Presenting the results
Two questions were formulated in this research synthesis; (1) what features of human
body odor have been studied in the research during the past five years? (2) How can these
features be presented in a biopsychosocial model?
Features of human body odor from research from the past five years have now been
identified and presented using the biopsychosocial model’s different levels of analysis. Recent
research findings do indeed strongly advocate that human body odor communicates
meaningful information with behavioral, biological and social implication. To illustrate the
answer to the second question we hereby propose the keywords to be organized as shown in
Figure 2.
11
Bio
-
Neuronal
processing
MHC
Estrus
Steroid hormon
Gene
Contraception
Attractiveness
Affection
-
Perception
Culture
Diet
Social
Psycho
Figure 2. This figure illustrates the distrubution of features of human body odor in the
biopsychosocial model.
The model illustrates our integrated view of the research in the field of human body
odor. Through this model we clarify how seemingly disparate and separate features are
connected to each other. In the biopsychosocial model’s hub lays the biopsychosocial level of
analysis where one feature was identified: attractiveness. This can be interpreted as
attractiveness having a central function in human body odor communication. Attractiveness is
intimately related to mate choice but also kin recognition and avoidance of the unattractive or
unfamiliar. Two articles reviewed in this research synthesis have directly investigated how
human body odor modulates attractiveness. But we argue that all distinguished features can,
albeit in a less direct way, be said to modulate human body odor attractiveness. Human body
odor is processed differently than similar common odors. For example, the study conducted
by Lundström et al. (2008) found that smelling a friend’s body odor activated regions
previously seen for familiar stimuli, whereas smelling a stranger activated amygdala and
insular regions akin to what has previously been demonstrated for fearful stimuli, which is a
signal of something to be avoided. The biological features have been found to possibly
indicate fertility status and genetic information, signaling mate quality. Social features, such
as diet, have a great impact on human body odor feasibly signaling group belonging. As
previously mentioned in a quality II study, outbreeding avoidance may to some extent rely on
unattractiveness of highly unfamiliar odors. Psychological states can modulate body odor
consequently affecting attractiveness ratings. Perception of body odor can be altered by
romantic love, which is greatly connected with attractiveness. Results suggest that
contraceptive pill use could disrupt disassortative mate preference and that women using birth
control were found to be poorer than fertile women at assessing male attractiveness only by
olfaction. It should be noted that human body odor communication is controversial subject in
the scientific world (Doty, 2010).
We believe that the biopsychosocial model has helped us shed new light on the field of
human body odor by organizing recent research findings in an integrated way. We think that it
can act as a tool for future human body odor studies. The biopsychosocial model itself might
inspire further investigation to include all three levels of analysis in the study in order to
increase ecological validity, which we argue is achieved by using the model. And vice versa,
12
other studies may use the model in order to identify which features need to be controlled for
or even avoided in order to investigate a specific feature independently. The model can also
be seen as a renewable tool where features can be added, replaced and removed in order for
optimized use. By using it in the same manner that this study has, future investigations could
for example add more features to the model, and by doing so benefit from gaining clarity over
how those features are distributed.
Discussion
This research synthesis organizes previous research findings in an innovative way, and
by doing so, attempts to illustrate human body odor from a new point of view. We, the
authors, feel that the biopsychosocial model for human body odor provides clarity by
illustrating how multifaceted human body odor is and how many things affect and are affected
by human body odor. By organizing features into biological, psychological and social levels,
people might find inspiration for new studies that further investigates for example the
importance of human body odor for people in different societies. In addition to this, the model
facilitates future studies as it can act as a reminder of the importance of controlling features
that potentially could alter results, for example if one wishes to study one specific biological
feature, other biological, psychological as well as social features need to be monitored.
A critique that can be directed towards this review is that we choose to include the
research findings from only the previous five years, which could lead to a loss of preliminary
data; our reason for doing this, however, is due to time constraints, and therefore a limitation
of the number of studies included had to be made. Also, the free online encyclopedia
Wikipedia was used for many of the definitions in this research synthesis, which can be seen
as questionable. We, the authors, would however argue that Wikipedia is a good source of
information as publicized in a study in Nature where Wikipedia is said to be about as good a
source of accurate information as Britannica, regarded as one of the most scholarly of
encyclopedias (Giles, 2005). We would also like to add that all definitions’ accuracy was
always considered.
Another aspect worth mentioning is the fact that although we choose to analyze the
research findings from a socio-cultural point of view, we are not able to distinguish what the
differences are between cultures, we can only establish that there is a cultural factor involved.
For example, a majority of the studies we included had criteria of female participants to not
use contraceptive pills, or other hormonal methods of contraception. The rate of female use of
hormonal contraceptives is largely culturally dependent, and might be of variable ecological
validity depending on the country.
In our study, the quality of the reviewed articles is assessed with quality scales. This
assessment tool is based on the one created by Carlsson and Eiman (2003), although it was
adjusted to better suit our literature review, since their version was meant to be used in
clinical trials only. We were able to do this adjustment by studying other quality assessments
as well as reading recommendations for how and why to assess quality (Carlsson & Eiman,
2003). Our adjustments are basically a removal of some questions that were directly focused
on clinical practices, and more importantly a translation of the scales from Swedish to
English.
The use of quality scales has in itself been a subject for debate; some argue that the use
of different scales can in itself be the source of problems with methodology. For example,
Cochrane discourages the use of such scales since, amongst a range of problems; the
adjectives used in the scales may be subjected to individual appraisals (Higgins & Green
(eds.), 2011). In our review we face one challenge when it comes to the use of quality scales,
and this is when rating the literature reviews. According to our quality scale, a review has to
13
include a detailed definition of exactly how the literature search took place; however, a
majority of the reviews did not contain such an explanation, which makes it harder to
replicate the reviews. This said the reviews contain a lot of information, which is of great
importance for our research synthesis, so in this case the quality scales are mostly used in
order for us as authors to ensure that we interpreted the literature reviews in the same manner.
However, although faced with some challenges, we still choose to follow Coopers (2010)
recommendations to use quality scales in order to avoid variance in our ratings. Since we are
two authors of this research synthesis, a common way of rating the design as well as how well
the studies met our inclusion criteria, was necessary in order to achieve consistent ratings,
which improves reliability. By using scales we were also able to judge how much weight
should be placed on a particular study, according to the quality the study achieved.
Hence, human body odor has many features, on different levels of analysis, and with
this research synthesis we hope to have provided a further understanding of what recent
research findings has found about human body odor. We hope that the model will serve as a
tool for future studies, and moreover we hope to inspire future research to methodologically
design the studies in order to increase ecological validity by including social, biological and
psychological features, in order to investigate how human body odor is interpreted outside of
the laboratory in everyday life.
Acknowledgments
The authors wish to thank their supervisor Professor Mats J. Olsson for his constructive
discussions and helpful ideas and Kimmo Sorjonen for his invaluable feedback.
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17
Appendix
Table 2. The following illustrates how the article searches were conducted in the databases
Database
PubMed
Producer: United States
National Library of Medicine
(NLM), US
Web of Science
Producer: Thomson Scientific,
Thomson Reuters, USA
PsycINFO
Producer: American
Psychological Association,
Washington DC
Search terms
"body odour" OR "body odor"
Limits
Humans
Results
41
"body odour" OR "body odor" AND
human
-
63
"body odour" OR "body odor"
Humans
22
Table 3. The following is the tool used for quality assessment of literature reviews.
An Evaluation of Literature Reviews
Points
0
Missin
Abstract (purpose, method, results = 3 p)
Missin
Introduction
Not specified
Goal
Metho d
Choice of method
Not specified
Description of method / reliability
Not specified
Literature search
Not described
Selection (similar results, relevance)
Not acceptable
Scientific Quality of Studies Included
Not discussed
Results
Question Answered
No
Analysis of the Results
Not acceptable
Description of Results
Missin
Discussion and Conclusions
Discussion of Problems
Missin
Self-reflection, Sources of Error
Missin
Comparison with Previous Research
Missin
Correspondence with Results
Conclusion Missing
Aspects of the
Suitable Conclusion
No
Total Points (Max 42 p)
p
Quality I: 80%
Quality II: 70%
Quality II: 60%
18
1
1 out of 3
Meage
Unclear
2
2 out of 3
Mediocre
Mediocre
3
All of the above
Well written
Clear
Not relevant
Meage
Meage
Low
Low
Relevant
Mediocre
Mediocre
Mediocre
Mediocre
Able to replicate
Able to replicate
Good
Good
Yes
Low
Low
Mediocre
Mediocre
Good
Clear
Unclear
Low
Low
Mediocre
Good
Mediocre
Clear
Good
Low
Mediocre
Good
Yes
p
p
p
p
%
Quality
Table 4. The following is the tool used for quality assessment of quantitative studies.
An Evaluation of Quantitative Studies
Points
0
Abstract (purpose, method, results = 3 p)
Missing
Introduction
Missing
Goal
Not specified
Method
Choice of method
Not specified
Description of method / reliability
Not specified
Selection (number, description,
Not acceptable
representative)
"Drop outs"
Unspecified
Quality of analysis
Missing
Ethical Aspects
Not given
Results
Question Answered
No
Confounders
Not controlled for
Statistical Analysis (methods, significance,
Missing
calculations)
Analysis of Results
Not acceptable
Description of Results (tables, charts
Missing
etc.)
Discussion
Discussion of Problems
Missing
Self-reflection, Sources of Error
Missing
Comparison with Previous Research
Missing
Conclusion
Correspondence with Results
Conclusion Missing
Aspects of the Study)
Suitable Conclusion
No
Total Points (Max 46 p)
p
Quality I: 80%
Quality II: 70%
Quality II: 60%
19
1
1 out of 3
Meager
Unclear
2
2 out of 3
Mediocre
Mediocre
3
All of the above
Well written
Clear
Not relevant
Meager
Relevant
Mediocre
Reliable
Low
Mediocre
Good
>20%
Low
Given
5 -20%
Mediocre
<5%
High
Yes
Controlled for
Not appropriate
Good
Low
Mediocre
Good
Low
Mediocre
Clear
Unclear
Low
Low
Mediocre
Good
Mediocre
Clear
Good
Low
Mediocre
Good
Yes
p
p
p
p
%
Quality
Table 5. The following is a summary of the review articles reviewed for the analysis.
Title + year
Human oestrus
(2008)
Immune
Reactivity and
Attractiveness
(2010)
Environmental
effects on
human body
odour (2008)
Authors
Aim of the study
Gangestad, S. W.
& Thornhill R.
Investigate whether
human females still
have an oestrus phase
in their menstrual
cycle, and if this period
involves changes in
sexual behavior in
comparison to infertile
phases.
Method: participants,
design and method of
analysis
The definition of
"oestrus" is reviewed
as well as womens
sexual preferences
across the reproductive
cycle. Also reviewed is
womens extended
sexuality, the role of
counter-pair copulation
and if men have
counterpart
adaptations.
Results
Quality score
Keywords
Human oestrus does still appropriatly apply
and was not lost in evolution since empirical
data supports the fact that women are drawn
to indicators of genetic quality when fertile.
Men are also more attracted to women
during oestrus because of changes in
physical appearance.
Points: 28 (=67%)
Quality: 3
Menstrual cycle
Points: 19 (=45%)
Quality : NA
Excluded
Points: 33 (=79%)
Quality: 2
Affection, diet,
menstrual cycle
Grammer K. &
Oberzaucher, E.
Investigate the
biological function of
signals of
attractiveness.
Not specified
Attractiveness signals immune resistance.
Being attractive would thus be an honest
signal for an immune system that coped well
with the environmental challenges it was
exposed to during ontogeny. This is a
prerequisite for developmental stability,
which again affects the differentiation of
beauty characteristics. The argument is that
human preferences and mate choice criteria
have evolved in coevolution with parasites,
and that the current parasite load modulates
our decision making.
Havlicek, J. &
Lechanova, P.
Human body odour is
individually specific
and several lines of
evidence suggest that
to some extent it is
under genetic control.
There are however
numerous other sources
of variation, commonly
labelled as
environmental factors,
Not specified
Specific diet and some diseases have major
impact on variations in human body odour.
which are the main aim
of this paper. These
include: 1)
reproductive status, 2)
emotional state, 3) diet
and 4) diseases. We
primarily focus on
axillary and genital
odours as they have
been proposed to have
communicative
function.
MHC-correlated
mate choice in
humans: A
review (2009)
Current Issues in
the Study of
Androstenes in
Human
Chemosignals
(2010)
Havlicek, J. &
Roberts, S. C.
A critical review of
studies on MHCassociated mate choice
in humans. The areas
that are investigated
are; 1. Odor preference,
2. Facial preference, 3.
Actual mate choice
surveys. The aim is
also to investigate if
the studies themself
differ from each other
or are biased.
Reviewing
methodology of studies
to determine the source
of body odor, the
treatment of the body
odor stimuli, the
experimental designs,
identification of loci
under study, the
questions used in
questionnaires as well
as the repeatability of
the ratings for facial
attractiveness and mate
choice. How this is
done is unclear.
Relevant factors for individual preferences is
reproductive status and if the mating context
is long term or short term. Olfaction and
visual channels may act as complementary
systems to achieve an optimal level of
MHC-variation in offspring; visually
humans tend to search for similar MHC,
whilst olfactory indicates favouring of MHC
dissimilar mates.
Point: 41 (=98%),
Quality: 1
MHC
Havlicek, J.,
Murray, A. K.,
Saxton, T. K. &
Roberts, S. C.
It is suggested that
odor plays a role in
mediating social
behavior. This review
aims to identify key
active compounds,
evaluate the
quantification of
naturally occuring
concentration, what
concentrations should
A review of studies
within three fields;
1. Biochemistry and
androstenes
2. Psychophysical
Research using
androstenes
3. Psychological effects
The review results in suggestions on how to
improve future research. Androstenes
influence physiology, psychology and
behavior; exactly what key compounds are
responsible for this is still unclear.
Thresholds for ecologically valid
concentrations seem to vary, so screening
before initiating a study is recommended.
And lastly there seems to be clear indicators
of functional gender differences.
Exculded for
being too specific
about androstenes
and the
difficulties met
when doing
resaerch studies
on adrostenes.
Excluded
21
Human Body
Odour
Individuality
(2008)
Genetic
Influences on
Human Body
Odor: Genes to
the Axillae
(2010)
Lenochova, P. &
Havlicek, J.
Leyden, J. J. &
Preti, G.
be used in studies in
order to be a realistic
representation of "the
real world", review
elisit effects and
elucidation of
individual differences
in production rates (e.g.
do men produce more
androstenes than
women?).
The main aim of this
paper is to review
studies dealing with
different aspects of
body odour
individuality. We
mainly focus on odour
recognition of (1)
gender specific cues,
(2) self and sexual
partner cues, (3) kin
cues and (4) motherinfant cues.
Subsequently, we
discuss possible
proximal causes of
odour individuality.
Describe the
relationship between
the production of
axillary odorants and
variants in the
ABCC11 gene.
Not specified
Humans produce temporarily stable,
genetically mediated odour signatures and
possess the ability to recognise, discriminate
and identify other people through the sense
of smell. The capability of self, gender, kin
and non-kin odour recognition plays a role
in social interactions. It seems that despite
the stability of olfactory cues, the hedonic
quality of body odour may vary over time.
Points: 31
(=74%) Quality: 2
Gene,
perception
Not specified
Individuals who are homozygotic for a SNP
(538G>A) were found to have significantly
less of the characteristic axillary odorants
than either individuals who were
heterozygotic for this change or those who
had the wild-type gene. The 538G>A SNP
predominates in Asians who have nearly
complete loss of typical body odor.
ABCC11 is expressed and localized in
apocrine sweat glands. These findings are
remarkably similar to the ethnic distribution
Do not meet the
inclusion criteria
(too specific).
Excluded
22
and expression patterns for apocrine apoD, a
previously identified carrier of a
characteristic axillary odorant.
Functional
Neuronal
Processing of
Human Body
Odors (2010)
The steroids
considered as
human
pheromones
(2010)
The future of an
applied
evolutionary
psychology for
human
partnership
(2010)
Lundström, J. N.
& Olsson, M. J.
The aim is to provide
an overview of the
current knowledge of
how the human brain
processes body odors
and the potential
importance these
signals have for us in
everyday life.
Overview of current
knowledge of how the
human brain processes
body odors.
Behavioral studies using body odors as
stimuli suggest that the complex mixture
constituting human body odors is processed
in a unique way due to the high behavioral
relevance.
Points: 38 (=90%)
Quality: 1
Neuronal
processing
Rajchard, J.
Give a review over
what research has
found about human
pheromones
Not specified
-
Points: 13 (=31%)
Quality: NA
Excluded
Roberts, S. C.,
Miner, E. J. &
Shackelford, T. K.
Review evidence for
the effects of (1)
increasing exposure to
mass media, (2) the
advent of novel ways
to meet potential
partners, and (3)
cultural influences
which may disrupt or
alter the expression of
evolved mate
preferences. They
comment on the
potential for these
effects to influence
self-perception and
partner-perception,
Not specified
A common theme emerges, which is that
these effects may contribute to relationship
dissatisfaction and dissolution, with negative
implications for societal change.
Evolutionary psychology research may focus
on and offer informed approaches to
ameliorate these effects in the future.
Do not meet the
inclusion criteria
(not specifically
about human
body odor).
Excluded
23
with downstream
effects on relationship
satisfaction and
stability.
In the nose of
the beholder: are
olfactory
influences on
human mate
choice driven by
variation in
immune system
genes or sex
hormone levels?
(2010)
Roberts, T. &
Roiser, J. P.
The aim of the review
is to critically analyze
the findings of studies
investigating olfactory
preference in humans,
and their implications
for two contrasting
theories of mate
choice: that females
prefer the scent of
males with dissimilar
HLA to their own or
that androstenone play
a role in female mate
choice.
Analysis of the
findings of studies
investigating olfactory
preference in humans,
and their implications
for these two
contrasting theories of
mate choice.
24
Much of literature has thus far treated HLAderived compounds or androstene-derived
compounds separately. However, there is no
clear reason why the two should be mutually
exclusive. Much as body odor and
fluctuation asymmetry are posited to work in
conjunction, it may be that androstene works
in tandem with HLA-derived scents.
Summary of HLA mate choice hypotheses:
preferred mate HLA haplotype are dissimilar
(most diverse HLA haplotype),
heterozygous (‘best of a bad job’ highquality mate able to provide first-order
benefits and reasonable offspring quality),
rare (resistant to common parasites),
intermediate heterozygosity (ensuring the
maintenance of locally co-adapted gene
complexes along with HLA diversity) and
complementary (most diverse HLA
haplotype).
Points: 30 (=71%)
Quality: 2
MHC
Table 6. The following is a summary of the quantitative articles reviewed for the analysis.
Title + year
Authors
Aim of the study
The Potential
Hedonic Role
of Olfaction in
Sexual
Selection and
its Dominance
in Visual
Cross Modal
Interactions
(2010)
Capparuccini,
O., Berrie, C.
P. &
Mazzatenta,
A.
The aim of this study
was to investigate if
perfumes are
involved in human
chemosexual
communication
Is Mate Choice
in Humans
Chaix, R.,
MHCCao, C. &
dependant
Donnelly, P.
(2008)
Are humans’
preferences mediated
by MHCdissimilarities in
body odours (as in
other species like
rodents and fish)? E.g
is there mating
patterns that
encourage
heterozygosity in
MHC?
Method: participants, design and
method of analysis
Participants: 50 males (23.6+-2.1 years
old), 50 females (22.2 +-1.4 years old) in
their ovulator fase. The participants were
right-handed, heterosexuals, normosmotic
for n-butanol and non-smokers without
pathologies. Design: A double blind
experiment. The participants had to assess
the faces on neutral adjectives (familiarity,
confidence), less neutral adjectives (liking,
irritability) and on sexually related
adjectives (beauty, pleasantness, charm,
intensity, sexual interest and sexual
attraction) on a 10 point Likert scales, and
without them knowing perfume was
released into the room . The perfumes
used where commercially available. Data
analysis: Statistical analysis.
Participants: In the first test 30 African
couples and 30 European American
couples were analyzed for relatedness in
SNPs. In the second test 30 African
couples and 44 European American
couples were analyzed for their relatedness
in HLA. Design: A comparison was made
to see if there is a significant dissimilarity
in MHC between spouses in comparison to
similarity in the genome in general.
Method of analysis: Statistical analysis.
25
Results
Quality score
Keywords
Perfumes or so-called "nonpheromonal olfactory cues" seem to be
involved in mate selection. This means
that olfactory cues of this kind seem to
be able to dominate visual signs in a
cross modal interaction.
Excluded for
focusing on
perfumed products
thus not meeting our
inclusion criteria.
Excluded
The study suggests that, in some cases,
humans may rely on biological factors
in addition to social factors, when
choosing a mate. European Amerians
has a significantly more MHC
Points: 40 (=87%)
dissimilarities compared with genome
Quality: 1
and other random pairs. African
spouses show no similarities or
dissimilarities across the MHC region
(loci) in comparison to genome and
other random pairs.
MHC
Olfactory Cues
modulate
Facial
Attractiveness
(2007)
Investigate whether
Dematte, M.,
olfactory cues can
Osterbauer,
influate people’s
R. & Spence,
judgements of facial
C.
attractiveness.
Participants: 16 females (20-34 years)
who went through an initial screening for
normal sense of smell. Design: The
participants viewed faces and rated them
on a scale between 1 and 9. The faces were
either shown with clean air or combined
with 1 out of 4 odorants. Two stimuli were
pleasant (male fragrance and clean air) and
two were unpleasant (rubber and body
odor). These smells were all assessed in a
previous pilot study. The participants then
rated the attractiveness of 40 male faces;
these faces had also been assessed in a
pilot study. Method of analysis: Statistical
analysis.
Male faces were rated as significantly
less attractive when combined with
unpleasant odors. There were no
significant variations between type of
odors, which implies that it didn't
matter if the smells were relevant to
the faces, body odor and male
fragrance, or not, rubber.
Women not taking hormone-based
contraceptives and in the fertile phase
of their menstrual cycle did perceive
the dominant side (left) on left-handed
men as more masculine. An
explanation to this may be an activity
based asymmetri caused by a stronger
smell from the more used axillea,
which in turn results in a more intense
e.g. masculine smell.
The hypothesized emergence of a
Participants: 9 families with 2 children
parent-child mutual aversion for the
each. Altogether 8 pre-pubertal children (7- odor of opposite-sex family members
10 years) and 10 pubertal
at puberty was not found,
children/teenagers (11-18 years). Design:
contradicting one of the few studies on
All family members wore t-shirts during
the topic. However, some
three nights. They then completed
developmental changes were observed,
questionnaires and rated the body odors
including reduced aversion for odor of
from family members and unfamiliar
the same-sex parent, and increased
individuals. The following was rated;
ability of adults, compared to children,
pleasantness, intensity, masculinity and
to recognize odor of family members.
recognition. Method of analysis: Statistical Sex and personality (depressive and
analysis.
aggressive traits) also significantly
influenced odor judgments. Further
Points: 41 (=89%)
Quality: 1
Attractiveness
Participants: 38 men and 49 women (19Human
Study whether odor
35 years). Design: The male participants
Axillary Odor:
samples differ
were asked to wear cotton pads during 24
Are There
Ferdenzi, C., between left and right
hours. The body odors were then rated for
Side-Related
Schaal, B. & axillae from left vs
attractiveness, intensity and masculinity.
Perceptual
Roberts, S. C. right handed men
Odor samples from each axillae was rated
Differences?
when perceived by
as independent stimuli. Method of analysis:
(2009)
female raters.
Statistical analysis.
Excluded for
focusing on siderelated differences
and not on human
body odor
mechanisms thus not
meeting our
inclusion criteria.
Excluded
Investigation of
changes in body odor
perception around
puberty, a period that
Family Scents:
is often forgotten
Developmental
when it comes to
Ferdenzi, C.,
Changes in the
studies on odorSchaal, B. &
Perception of
mediated behavioral
Roberts, S. C.
Kin Body
changes. The reason
Odor? (2010)
for investigating this
is because puberty is
already known to
affect social needs
and emission of body
Points: 36 (=78%)
Quality: 2
Perception
26
odor as well as
perception of body
odor.
Beauty Is
Mostly in the
Eye of the
Beholder:
Olfactory
Versus Visual
Cues of
Attractiveness
(2008)
The Effect of
Meat
Consumption
on Body Odor
Attractiveness
(2006)
He sees, she
smells? Male
and female
reports of
sensory
reliance in
mate choice
contexts.
(2008)
Foster, J. D.
Havlicek, J.
&
Lenochova,
P.
Havlicek, J.
et. al.
research with larger samples is needed
to investigate the poorly explored issue
of how olfactory perception of self and
family members develops, and how it
could correlate with normal
reorganizations in social interactions at
adolescence.
Participants: 44 women (mean age 24)
rated the attractiveness by assessing body
odor and photographs of 21 men (mean age
23). Design: The men wore t-shirts during
two nights, and the attractiveness was
assessed either independently (body odor
and then photography) or together (body
odor and photography at the same time).
Method of analysis: Statistical analysis.
Participants: 30 women and 17 male
donors. Design: A within-subject
We know that body
experimental design was the women
odor is individual and assessed male body odors. The body odors
informational. But
were collected from pads that the men had
what do we know
worn during 24 hours after having
when it comes to
followed either a meat diet or a non-meat
assessing the
diet during 2 weeks before. After one
influence of dietary
month the same males changes diets and
components on our
the body odors were rated again. The body
body odor?
odors were assessed for attractiveness,
pleasantness, masculinity and intensity.
Method of analysis: Statistical analysis.
(Based on previous
Participants: 717 Czech students (17-19
research) Do women
years), as well as previous participants in a
ascribe a greater
similar study conducted in the USA.
importance to smell
Design: Students were asked to complete a
when choosing a
questionnaire with 7-scale questions on the
mate? Is this based on
importance of sensory cues in specific
sexual experience?
contexts. Method of analysis: Statistical
Do men assign a
analysis.
greater importance to
Do women rely more
on olfactory cues
when assessing how
attractive men are? If
this is the case, is
there a difference
between fertile and
infertile women?
27
Looking only at a picture of a man and
assessing the attractiveness gives a
better prediction of the "overall
attractiveness" (body odor and
Points: 33 (=72%)
picture). This is the same for all
Quality: 2
women, although fertile women are
better when assessing attractiveness
only by olfaction.
Ecological factors like eating habits
are a source of variability in body
odor. Red meat consumption has a
negative impact of perceived body
odor hedonicity. A non-meat diet was
found to be significantly more
attractive, more pleasant and less
intense. Relationship status as well as
at time in the menstrual cycle have an
influence.
Points: 41 (=89%)
Quality: 1
A replication of the previous study
was made when it comes to women
relying more on olfactory cues and
men more on visual cues (both in
Points: 28 (=61%)
partner choice and during sexual
Quality: 3
arousal). In non-sexual contexts
women still value smell. Culture
differences do appear when it comes to
prioritizing what aspects are important
Contraception,
attractiveness
Diet
Culture,
perception
visual cues? Is this
relevant across
cultures?
NonAdvertised
does not mean
Concealed:
Body Odor
Changes
Across the
Human
Menstrual
Cycle. (2006)
Body odor of
monozygotic
human twins:
a common
pattern of
odorant
carboxylid
acids (2009)
Males Sexual
Orientation
Affects
Sensitivity to
Androstene
(2009)
Testing the
Havlicek, J.,
presumption that the
Dvorakova,
fertile period in
R., Bartos, L.
human females is
& Flegr, J.
concealed.
in one’s partner. Americans seems to
be more visually oriented overall
whereas Czech women tend to rate a
strong male body odor as something
positive.
Participants: 12 women (19-27 years) and
42 male raters (19-34 years). Design: The
women whore cotton pads for 24 hours
during the menstrual, the follicular and the
luteal cycle phase. The men then rated the
intensity, pleasantness, attractiveness and
femininity of the odors. Method of
analysis: Statistical analysis.
Men can potentially use smell to
monitor the menstrual phase a
prospective mate is in. Therefore, the
fertile period is non-advertised in
humans, but not concealed. During the
fertile phase of the menstrual cycle
Points: 37 (=80%)
(the follicular phase) the body odor
Quality: 1
was rated as less intense and more
attractive than in the non-fertile
phases. Significant changes across the
menstrual cycle were found in all
categories except for rated
"femininity".
Menstrual
cycle
Participants: 14 pairs of monozygotic
twins (2 of which were disqualified).
Design: Axilla secretion was sampled
twice by the participants wearing pads. The
samples were then treated in order to avoid
bacterial metabolism. Method of analysis:
Statistical analysis.
There was a clustering of samples
taken from monozygotic twins.
Specific pattern for volatile carboxylic
Points: 39 (=85%)
acids is subject to a day to day
Quality: 1
variation although the smell is also
dependent on strong genetic
contributions.
Gene
Kuhn, F &
Natsch, A.
A quantitative
investigation of
volatile carboxylic
acids (odorants) in 12
pairs of monozygotic
twins.
Lubke, K.,
Schablitzky,
S. & Pause,
B. M.
Participants: 13 homosexual men and 14
heterosexual men (between 18-40 years,
mean age was 25,4 years). Design: the
An investigation of
participants were to smell body odor,
whether male sexual
isovaleric acids were used as a control
orientation influences
substance. The odor was assessed by rating
perception of
sensitivity, subjective ratings of intensity,
androstene, which is
pleasantness, unpleasantness, familiarity as
a human social
well as self-reported emotional responses
chemosignale.
(valence, arousal and dominance) . The
ratings were made on a scale between 0-10.
Method of analysis: Statistical analysis.
28
Homosexual men have a higher
olfactory sensitivity to odor of
androstenes, this was compared to the
control substance where there were no
differences. Therefore, sexual
orientation has a significant impact on
perception of androstene but this does
not necessarily extend to the selfreported emotional responses.
Points: 36 (=78%)
Quality: 2
Steroid
hormones
Functional
Neuronal
Processing of
Body Odors
Differs from
that of Similar
Common
Odors (2008)
By means of positron
emission
tomography, the aim
was to elucidate the
Lundstrom, J.
neuronal substrates
N., Boyle, J.
behind body odor
A., Zatorre,
perception to answer
R. J. &
the question of
Joneswhether the central
Gotman, M
processing of body
odors differs from
perceptually similar
nonbody odors.
Participants: 15 healthy, right-handed,
nulliparous, nonsmoking women (mean
age 23 years) recruited from the
university’s student body, with an absence
of nasal congestion, sinus infection,
allergies, or decreased olfactory function.
Body odors were collected from each
participant and her long-time close friend
(mean length of friendship, 60 months).
Design: the PET session consisted of 5
odor conditions (odor-free baseline, odor
control, self, friend, and stranger), each
presented twice in a pseudo-randomized
order, yielding a total of 10, 60-s scans.
Participants were informed that all body
odors within each scan would originate
from the same identity category. Special
care was taken to assert that body odors in
the category Stranger had not been
presented to the participant during the
aforementioned behavioral testing to
prevent familiarization with the odor.
Method of analysis: Imaging analysis
29
Body odors were processed by a
network that was distinctly separate
from common odors, indicating a
separation in the processing of odors
based on their source. Smelling a
friend’s body odor activated regions
previously seen for familiar stimuli,
whereas smelling a stranger activated
amygdala and insular regions akin to
what has previously been
demonstrated for fearful stimuli.
Points: 46 (=100%)
Quality: 1
Neuronal
processing
The Neuronal
Substrates of
Human
Olfactory
Based Kin
Recognition
(2009)
Participants: 12 healthy, right-handed,
nulliparous, nonsmoking women (mean
age 24 years) with an absence of nasal
congestion, sinus infection, allergies, or
decreased olfactory function. Design: In
experiment 1, the ability to identify
individual body odors was assessed in a
Kin recognition based counterbalanced order using a
on body odors is done psychophysical testing paradigm. A threepredominantly
alternative, no feedback, forced-choice task
without conscious
with nine repetitions for each body odor
recognition. The aim category (sister and friend), with body
Lundstrom, J. of this study was to
odors from strangers as foils, was
N., Boyle, J. map the neural
administered. In experiment 2, the PET
A., Zatorre,
substrates of human
session consisted of four conditions [odorR. J. &
kin recognition by
free baseline, odor control, sister’s body
Jonesacquiring measures of odor, and friend’s body odor, each repeated
Gotman, M. regional cerebral
twice in a pseudo-randomized order.
blood flow from
Method of analysis: In experiment 1,
women smelling the behavioral identification performance
body odors of either
above chance value for each body odor
their sister or their
category was assessed with separate onesame-sex friend.
sample Student’s t-tests. To identify the
neuronal substrates of kin recognition, the
activations obtained while smelling the
sister with activations obtained while
smelling the friend were contrasted. A
conjunction analysis was performed to
explore regions that were commonly
activated in the two kin detection contrasts.
30
The initial behavioral experiment
demonstrated that accurate
identification of kin is performed with
a low conscious recognition. The
subsequent neuroimaging experiment
demonstrated that olfactory based kin
recognition in women recruited the
frontal-temporal junction, the insula,
and the dorsomedial prefrontal cortex;
Points: 46 (=100%)
the latter area is implicated in the
Quality: 1
coding of self-referent processing and
kin recognition. It is further shown that
the neuronal response is seemingly
independent of conscious
identification of the individual source,
demonstrating that humans have an
odor based kin detection system akin
to what has been shown for other
mammals.
Neuronal
processing
Olfactory
Event-Related
Potentials
Reflect
Individual
Differences in
Odor Valence
Perception
(2006)
The aim of the study
was to investigate the
reflections of
perceived quality on
olfactory ERPs. It is
difficult to assess
individual differences
when trying to
understand the neural
substrates of
perceived quality in
olfaction in studies
Lundstrom, J.
using odorants.
N., Seven, S.,
Therefore, this is an
Olsson, M. J.,
investigation of how
Schaal, B. &
individual differences
Hummel, T.
in perceived quality
of androstenes odor,
can be better
understood when put
into a continuum. The
rated valence of these
same stimuli could
then be investigated
by looking at the
olfactory event
related potentials of
the continuum.
Participants: A total of 22 healthy, righthanded, normosmic participants (11
women) with a mean age of 26.6 years
participated in the study. These participants
were selected from an initial group
consisting of 43 individuals who were
screened for consistency in their verbal
descriptors and sensitivity for the odor of
androstenone. Design: This was an
investigation of how individual differences
in perceived quality of androstenes odor,
can be better understood when put into a
continuum. The rated valence of these
same stimuli could then be investigated by
looking at the olfactory event related
potentials of the continuum. The difference
in the early cortical processing of
androstenone between 2 established groups
was studied differing only in their
perceived quality of androstenone. The
dimensions of rated valence and intensity
were especially monitored. Further,
hydrogen sulfide (H2S) was used as a
control odor to monitor valence which
most people describe as unpleasant (smell
of rotten eggs). Method of analysis:
psychophysical testing,
electrophysiological recording and
perceptual ratings.
31
The aim of the study was to investigate
the reflections of perceived quality on
olfactory ERPs, by studying the
differences. Results of the present
Excluded because
study suggest that the
too specific.
pleasantness/unpleasantness aspect of
odors is represented in the late
positivity of olfactory ERPs.
Excluded
Romantic love
modulates
Lundtröm, J.
women's
N. & Jonesidentification
Gotman, M.
of men's body
odors (2009)
Investigate the role of
the following
mechanisms:
(1)increased attention
toward current
partner or
(2)deflected attention
away from potential
novel partners in
relationships by
assessing the ability
of human participants
to identify individual
body odors. Here, this
question is addressed
by investigating
whether a
heterosexual woman's
ability to identify the
body odor of her
romantic partner, and
that of a male and
female friend, is
influenced by the
degree of romantic
love she feels towards
her partner.
Participants: 20 nulliparous, self-described
exclusively heterosexual women in
different stages of their menstrual cycle.
Their male partner and two close
heterosexual friends participated as body
odor donors. Only couples that had been
together for 12–36 months and had
expressed deep romantic love towards each
other in a semi-structured interview were
included in the study. Design: Here, this
question is addressed by investigating
whether a heterosexual woman's ability to
identify the body odor of her romantic
partner, and that of a male and female
friend, is influenced by the degree of
romantic love she feels towards her
partner. Ability to identify an individual's
body odor was assessed for each body odor
category in a three-alternative, nofeedback, forced-choice task with seven
trials, using the target body odor and the
odors of two same-sex strangers as lures.
The body odor collected from the other
participants' friends or boyfriends were
used as the odors of strangers. Method of
analysis: Statistical analysis
Results indicated that romantic love
deflects attention away from potential
new partners rather than towards
present partner.
Points: 45 (=98%)
Quality: 1
Perception
Scent of a
Woman: Men's
Testosterone
Miller S. L.
Responses to
& Maner J.
Olfactory
K.
Ovulation
Cues (2010)
Examine the extent to
which olfactory cues
to female ovulation—
scents of women at
the peak of their
reproductive
fertility—influence
endocrinological
responses in men.
Participants: 37 men in study 1 and 38
men in study 2 (18–23 years). Design: Men
in the current studies smelled T-shirts worn
by women near ovulation or far from
ovulation (Studies 1 and 2) or control Tshirts not worn by anyone (Study 2).
Method of analysis: To predict
participants’ testosterone levels after
smelling the women’s T-shirts (post smell
testosterone), statistical analysis were
performed.
Men exposed to the scent of an
ovulating woman displayed higher
levels of testosterone than did men
exposed to the scent of a nonovulating woman or a control scent.
Hence, olfactory cues signaling
women’s levels of reproductive
fertility were associated with specific
endocrinological responses in men.
Points: 42 (=91%)
Quality: 1
Menstrual
cycle, steroid
hormones
32
Ovulatory
cycle effects
on tip earnings
by lap dancers:
economic
evidence for
human estrus?
(2007)
Individual and
gender
fingerprints in
human body
odor (2007)
Male steroid
hormones and
female
preference for
male body
odor (2006)
Miller, G.,
Tybur, J. M.
& Jordan, B.
D.
To see whether estrus
still exists, the
ovulatory cycle
effects on tip earnings
by professional lap
dancers working in
gentlemen's clubs
were examined.
Participants: 18 dancers. Design:
Participants recorded their menstrual
periods, work shifts, and tip earnings for
60 days (representing about 5300 lap
dances) on a study web site. Method of
analysis: Statistical analysis.
Participants: Subjects were from large
families (89 males, 108 females, ages 18–
91, mean 44 years) living in a small village
in the Austrian Alps. Design: axillary
sweat, urine and saliva were collected. Five
Investigate if
sweat samples per subject were collected
individuals have their
over 10 weeks using a novel skin sampling
Penn, D. J.
own distinctive scent,
device and was analyzed for compounds.
et.al.
analogous to a
Method of analysis: the samples were
signature or
analyzed using stir bar sorptive extraction
fingerprint.
in connection with thermal desorption gas
chromatograph–mass spectrometry (GC–
MS), and the chromatographic profiles
were then statistically analyzed using
pattern recognition techniques.
To examine how
Participants: 76 nonsmoking Caucasian
human scent works as
women (age mean=23.18 years)
a signal in mate
participated by sniffing the T-shirts and 19
selection by
men aged 20 to 35 donated body odor and
investigating whether
saliva. Design: To test whether
women’s olfactory
Rantala, M.
attractiveness or intensity of male body
preferences for a
J., Eriksson,
odor is correlated with salivary
man’s scent could be
C., Vainikka,
concentrations of testosterone, estradiol, or
correlated with his
A. & Kortet,
cortisol the women were asked to rate the
testosterone,
R.
men’s body odor. The women were also
estradiol, or cortisol
sorted as contraceptive users and nonconcentrations, and
contraceptive users and asked to rate the
whether these
men’s body odor during different stages of
preferences change
their menstrual cycle. Method of analysis:
along with the
Statistical analysis.
menstrual cycle.
33
Normally cycling participants earned
about US$335 per 5-h shift during
estrus, US$260 per shift during the
luteal phase, and US$185 per shift
during menstruation. By contrast,
participants using contraceptive pills
showed no estrous earnings peak.
Do not meet the
inclusion criteria
because the article
does not directly
address human body
odor.
Excluded
More volatile compounds were found
in axillary sweat than in urine or
saliva, and among these, 373 peaks
consistent over time were found.
Among these candidate compounds
the chemical structures of 44
Points: 39 (=85%)
individual and 12 gender-specific
Quality: 1
volatile compounds were found. These
individual compounds provide
candidates for major
histocompatibility complex and other
genetically determined odors.
Gene
Women in their most fertile period
gave the highest attractiveness ratings
to all men, a finding in line with
previous studies. However, the
intensity ratings by women at different
menstrual phases did not significantly
differ statistically. It was found that
Points: 36 (=78%)
cortisol concentration in saliva
Quality: 2
correlated positively with the
attractiveness but not with the intensity
ratings of male T-shirt odor by all
women’s groups. However, neither
testosterone nor estradiol was
significantly associated with the
ratings of attractiveness or intensity.
Steroide
hormones
Participants: 35 heterosexual males (19-35
years, non-smokers, students). 8 female
raters. Design: Repeated-measures withinsubject experimental design. First there
Manipulation
was a collection of baseline info. The
of body odour
Testing the effects of males were divided into to groups and then
alters men's
a double blind
an application of underarm spray each day
selfmanipulation of
(either a fragranced deodorant with
confidence and Roberts, S.C.
personal odour on
antimicrobial ingredients and fragrance oil,
judgements of et. al.
self-confidence, rated or a placebo deodorant without these
their visual
attractiveness and
ingredients). Then the self-confidence was
attractiveness
behaviour.
measured 15 minutes before and 48 hours
by women.
after the application with a questionnaire.
(2009)
For the behavioural control, filming took
place. And for the rating of attractiveness
images were taken. Method of analysis:
Statistical analysis.
Genes in the major
histocompatibility
Participants: 193 women aged 18–35 were
complex (MHC)
registered and 97 of these completed the
influence individual
experiment (attended both sessions). The
odors and females
MHCwomen were genotyped at HLA-A, -B and
often prefer odor of
correlated
-DRB1. Male participants were 97
Roberts, S.
MHC-dissimilar
odour
heterosexual, non-smoking students or
C., Gosling, males. Women using
preferences in
staff, aged 18–35. Body odor was collected
L. M., Carter, oral hormonal
humans and
from male participants and they were also
V. & Petrie, contraceptives have
the use of oral
genotyped. Design: the women were tested
M.
been reported to have
contraceptives
before and after initiating pill use in a
the opposite
(2008)
longitudinal design; a control group of
preference. Here, the
non-users were tested with a comparable
aim is to test whether
interval between test sessions. Method of
contraceptive pill use
analysis: Statistical analysis.
alters odor
preferences.
34
A significant increase in selfconfidence when using a fragranced
deodorant and a significant decrease in
self-rated attractiveness can be
Points: 31 (=67%)
induced with a placebo deodorant.
Quality: 3
Outside raters show the same results
by assessing visible non-verbal
behaviour. Self-esteem can therefore
be seen as flexible.
Affective
states
There was no significant difference in
ratings between odors of MHCdissimilar and MHC-similar men
among women during the follicular
cycle phase. However, single women
preferred odors of MHC-similar men,
while women in relationships
preferred odors of MHC-dissimilar
Points: 43 (=93%)
men. A significant preference shift
Quality: 1
towards MHC-similarity associated
with pill use, which was not evident in
the control group. If odor plays a role
in human mate choice, the results
suggest that contraceptive pill use
could disrupt disassortative mate
preferences.
MHC,
contraception