Human Body Odor from a Biopsychosocial Approach A Research Synthesis

Department of Clinical Neuroscience Undergraduate program in Psychology, 6th semester Bachelor thesis in psychology (2PS013), 15 hp Spring semester 20...
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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

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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.

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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 5

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

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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 7

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

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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.

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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.

References Capparuccini, O., Berrie, C. P., & Mazzatenta, A. (2010). The potential hedonic role of olfaction in sexual selection and its dominance in visual cross-modal interactions. Perception, 39, 1322 – 1329. Carlsson, S., & Eiman, M. (2003). Evidensbaserad omvårdnad: studiematerial för undervisning inom projektet " evidensbaserad omvårdnad - ett samarbete mellan Universitetssjukhuset MAS och Malmö Högskola". (Rapport nr. 2). Malmö: Malmö Högskola. Chaix, R., Cao, C., & Donnelly, P. (2008). Is mate choice in humans MHC-dependent? Public Library of Science Genetics, 4, retrieved from http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1000184 Cooper, H. M. (2010). Research synthesis and meta-analysis: a step-by-step approach. Los Angeles: SAGE. Dematte, M. L., Osterbauer, R., & Spence, C. (2007). Olfactory cues modulate facial attractiveness. Chemical Senses, 32, 603-610. Doty, R. L. (2010). The great pheromone myth. Baltimore: John Hopkins University Press. Ferdenzi, C., Schaal, B., & Roberts, S. C. (2009). Human axillary odor: Are there side-related perceptual differences? Chemical Senses, 34, 565-571. Ferdenzi, C., Schaal, B., & Roberts, S. C. (2010). Family scents: developmental changes in the perception of kin body odor? Journal of Chemical Ecology, 36, 847-854. Foster, J. D. (2008). Beauty is mostly in the eye of the beholder: olfactory versus visual cues of attractiveness. The Journal of Social Psychology, 148, 765-773.

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Gangestad, S. W., & Thornhill, R. (2008). Human oestrus. Proceedings of the Royal Society B-Biological Sciences, 275, 991-1000. Giles, J. (2005, December 14). Internet encyclopaedias go head to head. Nature. Retrieved from http://www.nature.com/nature/journal/v438/n7070/full/438900a.html Grammer, K., & Oberzaucher, E. (2010). Immune reactivity and attractiveness. Gerontology, 56, 521-524. Havlicek, J., Dvorakova, R., Bartos, L., & Flegr, J. (2006). Non-advertized does not mean concealed: body odour changes across the human menstrual cycle. Ethology, 112, 8190. Havlicek, J., & Lenochova, P. (2006). The effect of meat consumption on body odor attractiveness. Chemical Senses, 31, 747-752. Havlicek, J., & Lenochova, P. (2008). Environmental effects on human body odour. In J. L. Hurst, R. J. Beynon, S. C. Roberts & T. D. Wyatt (Eds.), Chemical signals in vertebrates 11. New York: Springer-Verlag New York Inc. Havlicek, J., Murray, A. K., Saxton, T. K., & Roberts, S. C. (2010). Current issues in the study of androstenes in human chemosignals. Vitamines & Hormones, 83, 47-81. Havlicek, J., & Roberts, S. C. (2009). MHC-correlated mate choice in humans: A review. Psychoneuroendocrinology, 34, 497-512. Havlicek, J., Saxton, T. K., Roberts, S. C., Jozifkova, E., Lhota, S., Valentova, J. et al.(2008). He sees, she smells? Male and female reports of sensory reliance in mate choice and non-mate choice contexts. Personality and Individual Differences, 45, 565-570. Higgins, J.P.T., & Green, S. (editors). Cochrane handbook for systematic reviews of interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011, from www.cochrane-handbook.org. Kuhn, F., & Natsch, A. (2009). Body odour of monozygotic human twins: a common pattern of odorant carboxylic acids released by a bacterial aminoacylase from axilla secretions contributing to an inherited body odour type. Journal of the Royal Society Interface, 6, 377-392. Lenochova, P., & Havlicek, J. (2008). Human body odour individuality. In J. L. Hurst, R. J. Beynon, S. C. Roberts & T. D. Wyatt (Eds.), Chemical signals in vertebrates 11. New York: Springer-Verlag New York Inc. Leyden, J.J., & Preti, G. (2010). Genetic influences on human body odor: genes to the axillae. Journal of Investigative Dermatology, 130, 344–346. Lubke, K., Schablitzky, S., & Pause, B. M. (2009). Male sexual orientation affects sensitivity to androstenone. Chemosensory Perception, 2, 154-160. Lundström, J. N., Boyle, J. A., Zatorre, R. J., & Jones-Gotman, M. (2008). Functional neuronal processing of body odors differs from that of similar common odors. Cerebral Cortex, 18, 1466-1474. Lundström, J. N., Boyle, J. A., Zatorre, R. J., & Jones-Gotman, M. (2009). The neuronal substrates of human olfactory based kin recognition. Human Brain Mapping, 30, 2571-2580. Lundström, J. N., & Jones-Gotman, M. (2009). Romantic love modulates women's identification of men's body odors. Hormones and Behavior, 55, 280-284. Lundström, J. N., & Olsson, M. J. (2010). Functional neuronal processing of human body odors. Vitamins and Hormones: Pheromones, 83, 1-23. Lundström, J. N., Seven, S., Olsson, M. J., Schaal, B., & Hummel, T. (2006). Olfactory eventrelated potentials reflect individual differences in odor valence perception. Chemical Senses, 31, 705-711.

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Miller, G., Tybur, J. M., & Jordan, B. D. (2007). Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus? Evolution and Human Behavior, 28, 375-381. Miller, S. L., & Maner, J. K. (2010). Scent of a woman: men's testosterone responses to olfactory ovulation cues. Psychological Science, 21,276-283. Myers, D. G. (2006). Psychology. New York: Worth Publishers. Penn, D. J., Oberzaucher, E., Grammer, K., Fischer, G., Soini, H. A., Wiesler, D. et.al (2007). Individual and gender fingerprints in human body odour. Journal of the Royal Society Interface, 4, 331-340. Rajchard, J. (2010). The steroids considered as human pheromones. Ethology Ecology & Evolution, 22, 311-315. Rantala, M. J., Eriksson, C., Vainikka, A., & Kortet, R. (2006). Male steroid hormones and female preference for male body odor. Evolution and Human Behavior, 27, 259-269. Roberts, S. C., Gosling, L. M., Carter, V., & Petrie, M. (2008). MHC-correlated odour preferences in humans and the use of oral contraceptives. Proceedings of the Royal Society B:Biological Sciences, 275, 2715-2722. Roberts, S. C., Little, A. C., Lyndon, A., Roberts, J., Havlicek, J., & Wright, R. L. (2009). Manipulation of body odour alters men's self-confidence and judgements of their visual attractiveness by women. International Journal of Cosmetic Science, 31, 47-54. Roberts, S. C., Miner, E. J., & Shackelford, T. K. (2010). The future of an applied evolutionary psychology for human partnership. Review of General Psychology, 14, 318-329. Roberts, T., & Roiser, J. P. (2010). In the nose of the beholder: are olfactory influences on human mate choice driven by variation in immune system genes or sex hormone levels? Experimental Biology and Medicine, 235, 1277-1281. Styrelsen för Utbildnings etikgrupp (2004). Etikprövning av studentarbeten på grundutbildningsnivå. (PM, godkänd av Styrelsen för utbildning 2004-10-13). Solna: Karolinska Institutet. Wikipedia. (2011a). Perspiration. Retrieved April 14, 2011, from http://en.wikipedia.org/wiki/Perspiration Wikipedia. (2011b). Communication. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Communication Wikipedia. (2011c). Affection. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Affection Wikipedia. (2011d). Attractiveness. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Attractiveness Wikipedia. (2011e). Hormonal contraception. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Hormonal_contraception Wikipedia. (2011f). Culture. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Culture Wikipedia. (2011g). Diet. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Diet_%28nutrition%29 Wikipedia. (2011h). Genes. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Genes Wikipedia. (2011h). Menstrual cycle. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Menstrual_cycle Wikipedia. (2011j). Major histocompatibility complex. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Major_histocompatibility_complex Wikipedia. (2011k). Human Brain. Retrieved April 18, 2011, from http://en.wikipedia.org/wiki/Human_brain 16

Wikipedia. (2011l). Perception. Retrieved April 14, 2011, from http://en.wikipedia.org/wiki/Perception Wikipedia. (2011m). Steroid hormone. Retrieved April 20, 2011, from http://en.wikipedia.org/wiki/Steroid_hormones Wikipedia. (2011n). Androstenone. Retrieved August 10, 2011, from http://en.wikipedia.org/wiki/Androstenone Wikipedia. (2011o). Attention. Retrieved July 8, 2011, from http://en.wikipedia.org/wiki/Attention Wilson, D. A., & Stevenson, R. J. (2006). Learning to smell: olfactory perception from neurobiology to behavior. Baltimore: John Hopkins University Press.

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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

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

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