The effect of meat consumption on body odor attractiveness

Body odours as putative chemosignals in the father-child relationship: New insights on paternal olfactory kin recognition and preference from infancy to adolescence

Children's body odours are effective chemical cues in the parent-child relationship. Mothers can recognize the odour of their child and prefer this odour over that of unfamiliar children. This effect is mediated by genetic similarity and developmental stage and is therefore suited to promote parental care at pre-pubertal stage, while facilitating incest avoidance at (post-)pubertal stage. The present study tested whether similar mechanisms apply to fathers. Therefore n = 56 fathers evaluated body odour samples of their own and of unfamiliar children in varying genetic and developmental stages. Genetic status was determined by human leucocyte antigen (HLA) profiling, developmental status by standardized assessment of pubertal status and steroid hormone concentration (estradiol, testosterone). Similar to mothers, fathers identified their own child's body odour above chance and preferred that odour. The paternal preference did not relate to HLA similarity but decreased with increasing age of the child. The decline was associated with higher pubertal stages in daughters only, which supports the hypothesis of odour-mediated incest prevention in opposite-sex parent-child dyads.

Mass Specthoscope: A Hand-held Extendable Probe for Localized Noninvasive Sampling of Skin Volatome for Online Analysis

Human skin emits a unique set of volatile organic compounds (VOCs). These VOCs can be probed in order to obtain physiological information about the individuals. However, extracting the VOCs that emanate from human skin for analysis is troublesome and time-consuming. Therefore, we have developed "Mass Specthoscope"─a convenient tool for rapid sampling and detecting VOCs emitted by human skin. The hand-held probe with a pressurized tip and wireless button enables sampling VOCs from surfaces and their transfer to the atmospheric pressure chemical ionization source of quadrupole time-of-flight mass spectrometer. The system was characterized using chemical standards (acetone, benzaldehyde, sulcatone, α-pinene, and decanal). The limits of detection are in the range from 2.25 × 10-5 to 3.79 × 10-5 mol m-2. The system was initially tested by detecting VOCs emanating from porcine skin spiked with VOCs as well as unspiked fresh and spoiled ham. In the main test, the skin of nine healthy participants was probed with the Mass Specthoscope. The sampling regions included the armpit, forearm, and forehead. Numerous skin-related VOC signals were detected. In the final test, one participant ingested a fenugreek drink, and the participant's skin surface was probed using the Mass Specthoscope hourly during the 8 h period. The result revealed a gradual release of fenugreek-related VOCs from the skin. We believe that this analytical approach has the potential to be used in metabolomic studies and following further identification of disease biomarkers─also in noninvasive diagnostics.

Intrinsic and extrinsic factors affecting axillary odor variation. A comprehensive review

Humans produce odorous secretions from multiple body sites according to the microbiomic profile of each area and the types of secretory glands present. Because the axilla is an active, odor-producing region that mediates social communication via the sense of smell, this article focuses on the biological mechanisms underlying the creation of axillary odor, as well as the intrinsic and extrinsic factors likely to impact the odor and determine individual differences. The list of intrinsic factors discussed includes sex, age, ethnicity, emotions, and personality, and extrinsic factors include dietary choices, diseases, climate, and hygienic habits. In addition, we also draw attention to gaps in our understanding of each factor, including, for example, topical areas such as the effect of climate on body odor variation. Fundamental challenges and emerging research opportunities are further outlined in the discussion. Finally, we suggest guidelines and best practices based on the factors reviewed herein for preparatory protocols of sweat collection, data analysis, and interpretation.

An integrative review: Human chemosensory communication in the parent-child relationship

Body odors serve as signals of kinship, with parents exhibiting a preference for the scent of their infants, and vice versa. The reciprocal perception of body odors can promote bonding through two mechanisms. Firstly, as an indirect pathway, through associative chemosensory learning, which leads to changes in proximity-seeking behaviors. Secondly, as a direct pathway, by eliciting the display of positive emotions, thereby reinforcing the mutual bond. Both mechanisms weaken as the child undergoes development due to changes in body odor expression and perception. This comprehensive review provides an overview of the current literature on chemosignals in the parent-child relationship, highlighting their significance in facilitating dyadic communication throughout the developmental span. Furthermore, future research perspectives are outlined to gain a better understanding of these benefits and, on the long run, derive potential interventions to strengthen parent child attachment.

Immunoactivation Affects Perceived Body Odor and Facial but Not Vocal Attractiveness

Several previous studies have shown that in mammals, the health status of conspecifics can be assessed based on perceptual cues. Olfactory, visual, or acoustic cues may lead to avoidant behavior, thus reducing the risk of contagion by close contact with infected individuals. We tested whether immune system activation after immunization leads to perceptible changes in body odor and facial and vocal attractiveness in humans. We have experimentally activated the immune system of male participants using vaccination against hepatitis A/B and meningococcus. Their body odor, facial photographs, and vocal recordings were collected before and 14 days after vaccination. Subsequently, the body odor samples, facial photographs, and vocal recordings were assessed by female raters for their attractiveness and healthiness. We have also measured skin coloration (from facial photographs and in vivo using a spectrophotometer), vocal parameters, and C-reactive protein (CRP) levels as a marker of inflammation. We found an increase in perceived body odor attractiveness, a decrease in facial attractiveness and healthiness, and no change in vocal attractiveness 14 days after vaccination compared to the prevaccination condition. Moreover, there was no change in facial coloration or vocal parameters between the prevaccination and postvaccination conditions. Prevaccination CRP levels were negatively associated with body odor and facial attractiveness and positively associated with body odor intensity. Overall, our results suggest that perceived body odor as well as facial but not vocal attractiveness may provide cues to activation of the immune response and that each modality may carry specific information about the individual's condition.

Deodorants and antiperspirants: New trends in their active agents and testing methods

Sweating is the human body's thermoregulation system but also results in unpleasant body odour which can diminish the self-confidence of people. There has been continued research in finding solutions to reduce both sweating and body odour. Sweating is a result of increased sweat flow and malodour results from certain bacteria and ecological factors such as eating habits. Research on deodorant development focuses on inhibiting the growth of malodour-forming bacteria using antimicrobial agents, whereas research on antiperspirant synthesis focuses on technologies reducing the sweat flow, which not only reduces body odour but also improves people's appearance. Antiperspirant's technology is based on the use of aluminium salts which can form a gel plug at sweat pores, obstructing the sweat fluid from arising onto the skin surface. In this paper, we perform a systematic review on the recent progress in the development of novel antiperspirant and deodorant active ingredients that are alcohol-free, paraben-free, and naturally derived. Several studies have been reported on the alternative class of actives that can potentially be used for antiperspirant and body odour treatment including deodorizing fabric, bacterial, and plant extracts. However, a significant challenge is to understand how the gel-plugs of antiperspirant actives are formed in sweat pores and how to deliver long-lasting antiperspirant and deodorant benefits.

An appeasing pheromone ameliorates fear responses in the brown rat (Rattus norvegicus)

The brown rat (Rattus norvegicus) is one of the major animals both in the laboratory and in urban centers. Brown rats communicate various types of information using pheromones, the chemicals that mediate intra-species communication in minute amounts. Therefore, analyses of pheromones would further our understanding of the mode of life of rats. We show that a minute amount of 2-methylbutyric acid (2-MB) released from the neck region can ameliorate fear responses both in laboratory rats and in wild brown rats. Based on these findings, we conclude that 2-MB is an appeasing pheromone in the brown rat. A better understanding of rats themselves would allow us to perform more effective ecologically based research on social skills and pest management campaigns with low animal welfare impacts, which might contribute to furthering the advancement of science and improving public health.

Investigating the human chemical communication of positive emotions using a virtual reality-based mood induction

Humans can communicate their emotions to others via volatile emissions from their bodies. Although there is now solid evidence for human chemical communication of fear, stress and anxiety, investigations of positive emotions remain scarce. In a recent study, we found that women's heart rate and performance in creativity tasks were modulated by body odors of men sampled while they were in a positive vs. neutral mood. However, inducing positive emotions in laboratory settings remains challenging. Therefore, an important step to further investigate the human chemical communication of positive emotions is to develop new methods to induce positive moods. Here, we present a new mood induction procedure (MIP) based on virtual reality (VR), that we assumed to be more powerful than videos (used in our previous study) to induce positive emotions. We hypothesized that, consequently, given the more intense emotions created, this VR-based MIP would induce larger differences between the receivers' responses to the positive body odor versus a neutral control body odor, than the Video-based MIP. The results confirmed the higher efficacy of VR to induce positive emotions compared with videos. More specifically, VR had more repeatable effects between individuals. Although positive body odors had similar effects to those found in the previous video study, especially faster problem solving, these effects did not reach statistical significance. These outcomes are discussed as a function of the specificities of VR and of other methodological parameters, that may have prevented the observation of such subtle effects and that should be understood more in-depth for future studies on human chemical communication.

Smells as Communication Pathways - why Emotions Pass through the Nose

For many species, the sense of smell is the most important sensory system for interacting with the environment and conspecifics. In contrast, the role of perception and communication of chemosensory information in humans has long been underestimated. The human sense of smell was considered less reliable, so that it was given less importance compared to visual and auditory sensory impressions. For some time now, a growing branch of research has been dealing with the role of the sense of sell in emotion and social communication, which is often only perceived subconsciously. This connection will be examine in more detail in this article. First, he basics regarding the structure and function of our olfactory system will be described for better understanding and classification. Then, with this background knowledge, the significance of olfaction for interpersonal communication and emotions will be discussed. Finally, we conclude that people suffering from olfactory disorders have specific impairments in their quality of life.

Exploring the interrelationship between the skin microbiome and skin volatiles: A pilot study

Unravelling the interplay between a human’s microbiome and physiology is a relevant task for understanding the principles underlying human health and disease. With regard to human chemical communication, it is of interest to elucidate the role of the microbiome in shaping or generating volatiles emitted from the human body. In this study, we characterized the microbiome and volatile organic compounds (VOCs) sampled from the neck and axilla of ten participants (five male, five female) on two sampling days, by applying different methodological approaches. Volatiles emitted from the respective skin site were collected for 20 min using textile sampling material and analyzed on two analytical columns with varying polarity of the stationary phase. Microbiome samples were analyzed by a culture approach coupled with MALDI-TOF-MS analysis and a 16S ribosomal RNA gene (16S RNA) sequencing approach. Statistical and advanced data analysis methods revealed that classification of body sites was possible by using VOC and microbiome data sets. Higher classification accuracy was achieved by combination of both data pools. Cutibacterium, Staphylococcus, Micrococcus, Streptococcus, Lawsonella, Anaerococcus, and Corynebacterium species were found to contribute to classification of the body sites by the microbiome. Alkanes, esters, ethers, ketones, aldehydes and cyclic structures were used by the classifier when VOC data were considered. The interdisciplinary methodological platform developed here will enable further investigations of skin microbiome and skin VOCs alterations in physiological and pathological conditions.

Dynamic influences on the neural encoding of social valence

Social signals can serve as potent emotional triggers with powerful impacts on processes from cognition to valence processing. How are social signals dynamically and flexibly associated with positive or negative valence? How do our past social experiences and present social standing shape our motivation to seek or avoid social contact? We discuss a model in which social attributes, social history, social memory, social rank and social isolation can flexibly influence valence assignment to social stimuli, termed here as 'social valence'. We emphasize how the brain encodes each of these four factors and highlight the neural circuits and mechanisms that play a part in the perception of social attributes, social memory and social rank, as well as how these factors affect valence systems associated with social stimuli. We highlight the impact of social isolation, dissecting the neural and behavioural mechanisms that mediate the effects of acute versus prolonged periods of social isolation. Importantly, we discuss conceptual models that may account for the potential shift in valence of social stimuli from positive to negative as the period of isolation extends in time. Collectively, this Review identifies factors that control the formation and attribution of social valence - integrating diverse areas of research and emphasizing their unique contributions to the categorization of social stimuli as positive or negative.

Do you often sniff yourself or others? Development of the Body Odor Sniffing Questionnaire and a cross-cultural survey in China and the USA

OBJECTIVES

Body odor can convey much information about an individual and thus we frequently engage in sniffing one's own and other people's body odor. However, there is scarce evidence on the within- and cross-cultural variation in body odor sniffing behaviors and no psychometric scale for specifically measuring such behaviors. Hence, our study aimed to develop the Body Odor Sniffing Questionnaire (BOSQ) and used it to make a cross-cultural comparison.

METHODS

In Study 1, 2,026 participants were recruited from our university, with one half used for exploratory factor analysis (EFA) to examine the factor structure of the BOSQ (sample 1) and the other half used for confirmatory factor analysis (CFA) to verify the factor structure (sample 2). In Study 2, 352 Chinese and 254 US participants were recruited to complete the BOSQ through Wenjuanxing and Amazon Mechanical Turk, enabling comparison of body odor sniffing behaviors across two cultures.

RESULTS

The Study 1 results showed that the BOSQ comprises 17 items in three factors: self-private body odor, others' body odor, and self-common body odor. The CFA results further supported that this three-factor model was a good fit. The Study 2 results showed that US participants scored higher overall and on the self-private body odor and others' body odor dimensions, whereas Chinese participants scored higher on the self-common body odor dimension.

CONCLUSIONS

The BOSQ demonstrated good reliability and validity, which is a useful tool for evaluating individuals' body odor sniffing behaviors. Cross-cultural difference existed as the US population reported a higher prevalence of body odor sniffing behavior, compared to the Chinese population.

Canine Smell Preferences—Do Dogs Have Their Favorite Scents?

Simple Summary

There are many products that are targeted to pet owners. One category of these products is dog repellents—strongly aromatized solutions designed to stop dogs from approaching and investigating particular areas; the second are cosmetics which should be pleasant for dogs. Dogs have a particularly sensitive sense of smell; therefore, strong scents may be very intense, and not always pleasant, stimuli. It is truly interesting, then, that canine cosmetic products often have very strong fragrances designed mostly to appeal to the dog owners, rather than to the dogs themselves. Indeed, the scents that dogs choose to put on their fur differ strongly from those of common cosmetics. Dogs choose mostly intense, animal-derived smells, such as feces or carcasses, so there is a need to differentiate between canine and human smell preferences. As there is limited scientific data related to canine smell preferences, the purpose of this study was to verify dogs’ reactions to selected scents, which can also be appealing to humans. Our study shows that dogs were more likely to interact with the scents of blueberry, blackberry, mint, rose, lavender, and linalol.

Abstract

The available evidence on dogs’ scent preferences is quite limited. The purpose of this study was to verify the canine response to selected odors that may also be preferred by humans. The experiment was performed using 14 adult dogs (10 female and 4 male) of different breeds, body size, and age (1–14 years). During the experiment, dogs were exposed to 33 odor samples: a neutral sample containing pure dipropylene glycol (control) and 32 samples containing dipropylene glycol and fragrance oils. The dog was brought to the experimental area by its handler, who then stopped at the entrance, unleashed the dog, and remained in the starting position. The dog freely explored the area for 30 s. All dog movements and behavior were recorded and analyzed. The methodology of observing the dogs freely exploring the experimental area allowed us to determine the smells that were the most attractive to them (food, beaver clothing). Our study shows that dogs interacted more frequently with the scents of blueberries, blackberries, mint, rose, lavender, and linalol.

Similar Trajectories in Current Alcohol Consumption and Tick-Borne Diseases: Only Parallel Changes in Time or Links Between?

In a modern world, both tick-borne diseases and alcohol consumption are among major public health threats. In the present opinion article, we pose the question, whether these two health problems: alcohol consumption and tick-borne diseases prevalence can be related. We hypothesize that it is possible due to at least three factors: outdoor places chosen for alcohol consumption, behavioral changes induced by alcohol, and possible stronger attraction of human hosts after alcohol consumption to ticks. Many important clues are coming from social studies about people’s preference of places to consume alcohol and from studies regarding the attraction of people consuming alcohol to mosquitos. These data, however, cannot be directly transferred to the case of alcohol consumption and ticks. Therefore, we suggest that more detailed studies are needed to better understand the possible individual attractiveness of people to ticks and ways alcohol may influence it.

What is the link between personality and food behavior?

A number of personality characteristics have been linked to various aspects of taste (gustation), trigeminal, and olfactory perception. In particular, personality traits have been linked to olfactory sensory thresholds and olfactory identification abilities, as well as to the sensory-discriminative aspects of taste/flavour perception. To date, much of the research in this area has focused on Sensation Seeking (including Experience Seeking, and Openness to Novel Experiences), with the latter being linked to a preference for spicy, and possibly also crunchy, sour, and bitter foods/drinks. Novelty-seeking has also been linked to a preference for salty foods, while anxious individuals appear to enjoy a much narrower range of foods. A bidirectional link has also been documented between taste and mood. Certain of the personality-based differences in taste/flavour perception and food behaviour have been linked to differences in circulating levels of neurotransmitters and hormones in both normal and clinical populations. Taken together, therefore, the evidence that has been published to date supports a number of intriguing connections between personality traits and taste perception/food behaviour.

Ability of dog owners to identify their dogs by smell

Several studies report that olfactory cues play an important role in human life; humans are essentially able to recognize other family members and friends by their odors. Moreover, recent studies report that humans are also able to identify odors of non-conspecifics. The aim of this study was to determine whether dog owners are able to identify their dogs by smell and distinguish the odor of their own dogs from those of other dogs. A total of 53 dog owners (40 females and 13 males of different ages) volunteered to take part in this study. A number of the participants (17) owned 2 dogs; these owners took part in the study twice (i.e., working with only one dog at a time). Sterile gauze pads were used to collect odor samples from the dogs. Each pad was placed in its own sterile glass jar (750 ml) with a twist off lid until the experiment commenced. Participants were asked to identify their own dog´s odor from a line-up of 6 glass containers. This experiment demonstrated that dog owners are capable of identifying their dogs by smell on a significant level. Results of this study additionally suggested that male owners outperformed their female counterparts in the identification process. Moreover, dog owners whose dogs were housed outside had a higher success rate in identification than did participants who kept their dogs indoors with them. The dog owners found it easier to identify dogs that had been neutered, fed dry dog food and bathed less frequently. In general, younger dog owners tended to have more success when attempting to identify their dogs than did their older counterparts.

Love Stinks: The Association between Body Odors and Romantic Relationship Commitment

Anecdotal reports indicate that women dislike their partner’s body odor (BO) during the breakdown of a relationship; however, whether disliking a partner’s BO is associated with intentions to break up has not been empirically tested. Therefore, the aim of the current study was to investigate, for the first time, whether disliking one’s partner’s BOs is associated with experiencing lower commitment to a romantic relationship. Eighty participants (48 partnered, 32 single and previously partnered) completed self-report questionnaires about their current or previous romantic relationship and the amount of exposure to—and hedonic ratings of—their current or former partner’s BOs. Olfactory function was also tested, and participants smelled and rated various pieces of clothing imbued with a stranger’s BO. The results demonstrated that for participants who had experienced a breakup, historically higher levels of relationship commitment were associated with higher hedonic ratings of a previous partner’s BOs, regardless of the type of BOs. For participants currently in a relationship, lower relationship commitment was associated with higher breakup intentions in response to smelling their partner’s BOs. These preliminary results contribute evidence for the positive association between exposure to a partner’s BOs and favorable hedonic appraisals of BOs; however, further research needs to be conducted in this area to investigate nuances. Lower levels of exposure to one’s partner’s BOs may be more indicative of relationship commitment than exposure to hedonically unpleasant BOs of one’s partner. The findings are discussed with reference to their implications for interventions in relationship breakdown.

No evidence for association between human body odor quality and immune system functioning

Previous studies have shown that women perceive male faces with a more reactive immune system as more attractive, but whether body odor might likewise provide cues to immune function has not been investigated yet. These two studies tested a possible relationship between body odor quality and immunoreactivity (Study 1) and immune system function (Study 2). In Study 1, we collected body odor samples from 21 men just before and two weeks after vaccination against hepatitis A/B and meningococcus. We determined the levels of specific antibodies (selected as markers of immune system's reactivity), testosterone, and cortisol. Subsequently, 88 female raters assessed the odor samples for their attractiveness, intensity, and healthiness. In Study 2, we collected body odor and blood samples from 35 men and women. We assessed key parameters of their innate and adaptive immunity, such as complement activity or total lymphocyte T and B counts and asked 95 raters to assess the odor samples for their attractiveness, intensity, and healthiness. In Study 1, we found no significant association between antibody levels induced by vaccination and perceived body odor attractiveness, intensity, and healthiness. We also found no significant relationship between antibody levels and steroid hormones (testosterone and cortisol). In Study 2, we likewise found no association between basal key parameters (innate and adaptive) of the immune system and body odor quality. Our results indicate that body odor may not serve as a cue to the reactivity of the immune system.

You See What You Smell: Preferential Processing of Chemosensory Satiety Cues and Its Impact on Body Shape Perception

The current study examines neural responses to satiety- and fasting-related volatiles and their effect on the processing of body shapes. Axillary sweat was sampled with cotton pads from 10 individuals after 12 h of fasting, and after having consumed a standard breakfast. Pure cotton pads served as the control. The chemosensory stimuli were presented to 20 participants (via a constant-flow olfactometer) exclusively, and additionally as context to images of overweight and underweight avatars. EEG was recorded (61 electrodes), and chemosensory (CSERPs; P1, N1, P2, P3) and visual event-related potentials (VERPs; N1, P2, P3a, P3b) were analyzed. The amplitudes of all positive CSERP components differed more strongly from cotton in response to chemosensory satiety cues as compared to fasting cues (P1: p = 0.023, P2: p = 0.083, P3: p = 0.031), paralleled by activity within the middle frontal and temporal gyrus. Overweight compared to underweight body shapes tended to elicit larger VERP P2 amplitudes (p = 0.068), and chemosensory satiety cues amplified the VERP amplitudes in response to any body shape (P2, P3a, P3b; all p_s ≤ 0.017) as compared to the cotton control. The results indicate that chemosensory satiety cues transmit complex social information, overriding the processing of analogous visual input.

Scent of a Woman-Or Man: Odors Influence Person Knowledge

First impressions of social traits are regularly, rapidly, and readily determined from limited information about another individual. Relatively little is known about the way that olfactory information, particularly from scents that are not body odors, alters a first impression. Can the attributes of an odorant be conferred onto a person associated with that scent? To explore this, 101 participants were asked to form an impression of a hypothetical person based on the following stimuli: A gender-neutral silhouette, a list of six personal characteristics, and one of five odorants. Participants then rated the likelihood that the hypothetical person possessed each of 51 personality traits that were determined a priori as falling into six attribute categories. Participants also directly rated all odorants for the six categories and intensity. A T-test showed that ratings of the hypothetical person were less disparate from the odor that was presented during impression formation than from other odors. ANOVA revealed that the effects were heterogeneous, with odorants varying in their effectiveness in associating the hypothetical person with categories. The present data suggest that a hypothetical person can be imbued with the specific attributes of an odor and that some odors are better at contributing to impressions than others.

The scent of attraction and the smell of success: crossmodal influences on person perception

In recent decades, there has been an explosion of research into the crossmodal influence of olfactory cues on multisensory person perception. Numerous peer-reviewed studies have documented that a variety of olfactory stimuli, from ambient malodours through to fine fragrances, and even a range of chemosensory body odours can influence everything from a perceiver's judgments of another person's attractiveness, age, affect, health/disease status, and even elements of their personality. The crossmodal and multisensory contributions to such effects are reviewed and the limitations/peculiarities of the research that have been published to date are highlighted. At the same time, however, it is important to note that the presence of scent (and/or the absence of malodour) can also influence people's (i.e., a perceiver's) self-confidence which may, in turn, affect how attractive they appear to others. Several potential cognitive mechanisms have been put forward to try and explain such crossmodal/multisensory influences, and some of the neural substrates underpinning these effects have now been characterized. At the end of this narrative review, a number of the potential (and actual) applications for, and implications of, such crossmodal/multisensory phenomena involving olfaction are outlined briefly.

Body Odours Sampled at Different Body Sites in Infants and Mothers-A Comparison of Olfactory Perception

Body odours and their importance for human chemical communication, e.g., in the mother-child relationship, are an increasing focus of recent research. Precise examination of sampling methods considering physiology and feasibility aspects in order to obtain robust and informative odour samples is therefore necessary. Studies comparing body odour sampling at different body sites are still pending. Therefore, we sampled axilla, breast, and head odour from 28 mother-infant dyads and examined whether odour perception differs with regard to the body site. The participating mothers were asked to evaluate their own and their infant's body odour samples, as well as odours of two unfamiliar mother-infant dyads. We tested whether maternal pleasantness and intensity evaluation, as well as recognition ability of the odours differed between the body sites. In infants, the head odour exhibited slightly lower pleasantness ratings than axilla and breast, and intensity ratings did not differ between body sites. In mothers, body site affected intensity ratings but not pleasantness ratings, as the breast odour was rated as less intense compared with head and axilla. Across all body sites, mothers rated the own and their infant's odour as less intense when compared with unfamiliar samples. Recognition ability did not differ between body sites, and in line with previous studies, mothers were able to recognize their own and their own infant's odour above chance. In sum, our study extends the previous methodological repertoire of body odour sampling and indicates that the axilla, breast, and head of adults as well as infants serve as informative odour sources.

The lasting smell of emotions: The effects of reutilizing fear sweat samples

A growing body of research has shown that human apocrine sweat carries information about the emotional state of its donor. Exposure to sweat produced in a fear-inducing context triggers in its receivers a simulacrum of this emotional state, as evidenced by increased medial frontalis and corrugator supercilii (facial electromyography; fEMG) activity – two facial muscles involved in the display of fear facial expressions. However, despite the increased interest in the effects of emotional sweat, little is known about the properties of these chemical sweat samples. The goal of this study was to examine whether a second application of the same sweat sample would yield reliable results. Specifically, we assessed whether sweat samples collected from Portuguese males (N = 8) in fear (vs. neutral)-inducing contexts would produce similar fEMG activations (i.e., in the medial frontalis and corrugator supercilii) in female receivers (N = 60) across two independent applications (the first with Dutch and the second with Portuguese receivers). Our findings showed that exposure to fear (vs. neutral) sweat resulted in higher activation of both muscles compared with neutral odors, revealing a similar data pattern across the two applications and underlining the feasibility of reusing emotional sweat samples. The implications of these findings for properties of these sweat volatiles are discussed.

Pheromone effects on the human hypothalamus in relation to sexual orientation and gender

Pheromones are chemicals that serve communicational purposes within a species. In most terrestrial mammals, pheromones are detected by either the olfactory epithelium or the vomeronasal organ and processed by various downstream structures including the medial amygdala and the hypothalamus to regulate motivated behaviors and endocrine responses. The search for human pheromones began in the 1970s. Whereas bioactive ligands are yet to be identified, there has been accumulating evidence that human body odors exert a range of pheromone-like effects on the recipients, including triggering innate behavioral responses, modulating endocrine levels, signaling social information, and affecting mood and cognition. In parallel, results from recent brain imaging studies suggest that body odors evoke distinct neural responses from those observed with common nonsocial odors. Two endogenous steroids androsta-4,16,- dien-3-one and estra-1,3,5(10),16-tetraen-3-ol are considered by some as candidates for human sex pheromones. The two substances produce sexually dimorphic effects on human perception, mood, and physiological arousal. Moreover, they reportedly elicit different hypothalamic response patterns in manners contingent on the recipients' sex and sexual orientation. Neuroendocrine mechanisms underlying the effects of human chemosignals are not yet clear and await future detailed analyses.

Variability in human attractiveness to mosquitoes

Blood-feeding mosquitoes locate humans spatially by detecting a combination of human-derived chemical signals, including carbon dioxide, lactic acid, and other volatile organic compounds. Mosquitoes use these signals to differentiate humans from other animals. Spatial abiotic factors (e.g. humidity, heat) are also used by mosquitoes to find a host. Mosquitoes cause discomfort and harm to humans, being vectors of many pathogens. However, not all humans suffer from mosquito bites with the same frequency or intensity. Some individuals are more attractive to mosquitoes than others, and this has an important impact on the risk of infection by pathogens transmitted by these vectors, such as arboviruses and malaria parasites. Variability in human attractiveness to mosquitoes is partially due to individual characteristics in the composition and intensity in the release of mosquito attractants. The factors that determine these particularities are diverse, modestly understood and still quite controversial. Thus, this review discusses the role of pregnancy, infection with malaria parasites (Plasmodium spp.), skin microbiota, diet, and genetics in human attractiveness to mosquitoes. In brief, pregnancy and Plasmodium infection increase the host attractiveness to mosquitoes. Skin microbiota and human genetics (especially HLA alleles) modulate the production of mosquito attractants and therefore influence individual susceptibility to these insects. There is evidence pointing to a role of diet on human susceptibility to mosquitoes, with some dietary components having a bigger influence than others. In the last part of the review, other factors affecting human-mosquito interactions are debated, with a special focus on the role of mosquito genetics, pathogens and environmental factors (e.g. wind, environmental disturbances). This work highlights that individual susceptibility to mosquitoes is composed of interactions of different human-associated components, environmental factors, and mosquito characteristics. Understanding the importance of these factors, and how they interact with each other, is essential for the development of better mosquito control strategies and studies focused on infectious disease dynamics.

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Individual human attractiveness to mosquitoes is highly variable.

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Mosquito attractants released into the air vary from person to person.

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Variation in attractiveness to mosquitoes alters the risk of mosquito-borne infections.

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Pregnancy, malaria infection, skin microbiota and genetic factors alter the release of mosquito attractants.

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Environment and mosquito-related factors affect human–mosquito interactions.

Individual Chemical Profiles in the Leach's Storm-Petrel

Avian chemical communication, once largely overlooked, is a growing field that has revealed the important role that olfaction plays in the social lives of some birds. Leach's storm-petrels (Oceanodroma leucorhoa) have a remarkable sense of smell and a strong, musky scent. This long-lived, monogamous seabird relies on olfaction for nest relocation and foraging, but whether they use scent for communication is less well studied. They are nocturnally active at the breeding colony and yet successfully reunite with their mate despite poor night-vision, indicating an important role for non-visual communication. We investigated the chemical profiles of Leach's storm-petrels to determine whether there is socially relevant information encoded in their plumage odor. To capture the compounds comprising their strong scent, we developed a method to study the compounds present in the air surrounding their feathers using headspace stir bar sorptive extraction coupled with gas chromatography-mass spectrometry. We collected feathers from Leach's storm-petrels breeding on Bon Portage Island in Nova Scotia, Canada in both 2015 and 2016. Our method detected 142 commonly occurring compounds. We found interannual differences in chemical profiles between the two sampling years. Males and females had similar chemical profiles, while individuals had distinct chemical signatures across the two years. These findings suggest that the scent of the Leach's storm-petrel provides sociochemical information that could facilitate olfactory recognition of individuals and may inform mate choice decisions.

Interdisciplinary challenges for elucidating human olfactory attractiveness

Many species use chemicals to communicate. In humans, there is increasing evidence that chemicals conveyed by the body are extremely important in interpersonal relationships. However, many aspects of chemical communication remain to be explored to fully understand this function in humans. The aim of this article is to identify relevant challenges in this field, with a focus on human attractiveness in the context of reproduction, and to put forward roadmaps for future studies that will hopefully extend to a wider range of social interactions. The first challenge consists in not being limited to body (mal)odours from the axilla. Preliminary data on how the odour of the face and head is perceived are presented. Second, there is a crucial need to increase our knowledge of the chemical bases of human chemical communication. Third, cross-cultural approaches must not be overlooked, because they have a major input in understanding the universal and culture-specific aspects of chemical communication. Fourth, the influence of specific cultural practices such as contraceptive and fragrance use is likely to be prominent and, therefore, needs to be well described. The fifth and last challenge for research projects in this field is the integration of different disciplines such as behavioural sciences, social sciences, neurosciences and microbiology. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Detection of axillary perspiration metabolites using ion mobility spectrometry coupled to rapid gas chromatography

The composition of human sweat-and as a consequence the composition of volatiles released from human skin-strongly depends on genetic preconditions, diet, stress, personal hygiene but also on health status and medication. Accordingly, the composition is a carrier of information on the physical and mental states of a person. Therefore, rapid on-site analysis of the relevant substances may be used for medical diagnosis and medication control or even for psychological characterisation. Ion mobility spectrometry coupled to rapid gas chromatography (GC-IMS) was applied to the analysis of human axillary sweat as a sensitive, selective, rapid, and non-invasive method in a feasibility study. For this purpose, a sampling chamber was designed and manufactured. The design and the experimental setup were validated successfully. At least 179 human metabolites could be detected by GC-IMS from the skin of 7 volunteers. Fifteen metabolites were available in all samples from all volunteers and therefore can be characterised as basic sweat compounds which might enable the localisation of hidden persons. Furthermore, in a preliminary feasibility study, the potential of GC-IMS for differentiating the composition of sweat after physical exercises and in a stressful situation-even gender specific-could be demonstrated. Thus, with GC-IMS, a rapid and mobile analytical tool for the analysis of skin volatiles is available for a broad range of applications, e.g. with regard to axillary odour, human health, nutrition, consumption of remedies or drugs of abuse, the localisation of trapped or hidden persons, or even the characterisation of the reaction on stressful situations. Graphical abstract.

Modulation of feed composition is able to make hens less attractive to the poultry red mite Dermanyssus gallinae

The poultry red mite (PRM) is an obligatory haematophagous pest that causes substantial economic losses in poultry worldwide. The PRM does not live on the host but in the bird's environment and must find its host remotely. Hence, manipulating chicken odours is of interest. Several crude plant-originating volatile organic compounds (VOCs) have already been shown as repellent to Dermanyssus gallinae. We aimed to test whether these VOCs can interfere with PRM host-seeking behaviour by their oral administration to the poultry. The objectives were to determine (1) if hen odours are modified by supplemented feed ingestion and (2) if such treatment makes hens less attractive to the PRM. Chemical characterization by gas chromatography-mass spectrometry of the hen odour was conducted before and after the hens ingested the supplemented feed. The chromatograms obtained show that hen odour was substantially modified after the hens consumed it. Among the molecules recurrently detected from the supplemented hens, 26% were nearly absent in the unsupplemented hens. Behavioural choice tests to compare the effect of the modified and unmodified-host odours on the PRM show that some of the plant-originating emitted VOCs and the modified whole-hen odours were repellent to the PRM.

Evidence for odour-mediated assortative mating in humans: The impact of hormonal contraception and artificial fragrances

There is substantial evidence for assortative partner preferences in humans based on physical characteristics. In contrast, evidence suggests that olfactory preferences tend to be disassortative, with people preferring body odour of potential partners who are dissimilar at key genetic loci, perhaps to gain fitness advantage through offspring heterozygosity. We compared ratings of perceived body odour similarity of real couples with those of randomly paired 'fake' couples. Contrary to prediction, we find that odours of real partners are perceived more, rather than less, similar to each other than fake couples. However, this applied only to natural odour samples: there were no differences in similarity levels of real and fake couples' samples which were collected while wearing artificial fragrances. Furthermore, in light of suggestions that hormonal contraception (HC) disrupts disassortative odour preferences in women, we compared odour similarity among real couples in which the female partner was using or not using HC at the time when the relationship began. We find that odours of HC-using couples are of intermediate similarity between non-using and fake couples, suggesting that HC use during partner choice could affect odour-influenced assortment. We also examined the association between relationship satisfaction and perceived similarity of unfragranced odours of real couples. We found that these are positively correlated in male partners but negatively correlated in the female partners, indicative of a sex difference in the relative favourability of odour similarity in partner preference. Finally, by comparing odour similarity ratings with those given by perfumers using a novel olfactory lexicon we found evidence that similarity judgements were based on the Spicy/Animalic aspects of individual odour profiles. Taken together, our results challenge the conventional view that odour-mediated partner preferences in humans are typically disassortative.

The effect of complete caloric intake restriction on human body odour quality

Previous studies on various vertebrates have shown that quantity and quality of food intake affect odour attractiveness as perceived by potential mates. In humans, the quality of body odour is similarly affected by ingested foods, such as by variation in meat and garlic intake. Nevertheless, it is not known whether quantity of food has an impact on human body odour attractiveness. Thus, here we tested how 48 h of complete caloric intake restriction affects the hedonic quality of human axillary odour. Odour samples (cotton pads fixed in both armpits and worn for 12 h) were obtained from healthy female donors across three conditions: i) during their habitual food regime; ii) after 48 h of complete caloric intake restriction (drinking water was provided), and iii) 72 h after restoration of caloric intake. Axillary samples were assessed by male raters regarding their pleasantness, attractiveness, femininity, and intensity. We also collected blood samples to assess physiological changes due to dietary restriction (e.g., glucose, sodium, albumin, and triacylglyceride assays) and anthropometric measurements at the same intervals as body odour samples. We found no differences in pleasantness, attractiveness and intensity between the odour samples collected at baseline and during complete caloric intake restriction. Interestingly, we found that body odours were rated more pleasant, more attractive and less intense after restoration of food intake as compared to the baseline and during caloric restriction. Our results suggest that restoration of food intake positively influences hedonic quality of human body odour which might thus provide cues to current fitness status and metabolic efficiency.

The role of body odors and olfactory ability in the initiation, maintenance and breakdown of romantic relationships - A review

The aim of this review is to present direct and indirect lines of converging evidence that highlight the many ways our body odors and sense of smell may influence the three broad stages of romantic relationships; initiation, maintenance and breakdown. This emerging area of study requires a multidisciplinary empirical approach. Here we survey research findings that taken together, suggest that body odor perception moderates mate choice, provides a source of comfort in existing relationships and may signal the breakdown of a relationship through disgust processes. In terms of olfactory ability, having a good sense of smell may facilitate identifying a healthy mate, enhance sexual experiences, relationship security and ensure empathic responsivity, predictors of relationship longevity. We therefore conclude that olfaction plays an important - yet understudied - role in romantic relationships.

Chemical composition of glandular secretions from a pair-living monogamous primate: Sex, age, and gland differences in captive and wild owl monkeys (Aotus spp.)

Broadening our knowledge of olfactory communication in strictly monogamous systems can inform our understanding of how chemosignals may facilitate social and reproductive behavior between the sexes. Compared to other social and mating systems, relatively little is known about olfactory communication in strictly monogamous non-human primates. Furthermore, platyrrhines are not well represented in chemical analyses of glandular secretions. We conducted semi-quantitative headspace gas chromatography with mass spectrometry to investigate the chemical components of glandular secretions from the subcaudal and pectoral glands of a strictly pair-living platyrrhine, the owl monkey (Aotus spp.). In this study, the first chemical analysis of a wild platyrrhine population, our goals were to (1) conduct a robust analysis of glandular secretions from both captive and wild owl monkey populations and (2) identify whether biologically relevant traits are present in glandular secretions. We also compared and contrasted the results between two Aotus species in different environmental contexts: wild Aotus azarae (N = 33) and captive A. nancymaae (N = 104). Our findings indicate that secretions from both populations encode sex, gland of origin, and possibly individual identity. These consistent patterns across species and contexts suggest that secretions may function as chemosignals. Our data also show that wild A. azarae individuals are chemically discriminated by age (adult or subadult). Among the captive A. nanycmaae, we found chemical differences associated with location, possibly caused by dietary differences. However, there was no noticeable effect of contraception on the chemical profiles of females, nor evidence that closely related individuals exhibit more similar chemical profiles in A. nancymaae. Overall, our data suggest that glandular secretions of both wild and captive Aotus convey specific information. Future studies should use behavioral bioassays to evaluate the ability of owl monkeys to detect signals, and consider whether odor may ultimately facilitate social and sexual relationships between male and female owl monkeys.

Do Single Men Smell and Look Different to Partnered Men?

Previous research indicates human body odor (BO) can signal kinship, sickness and genetic compatibility. Based on research indicating single males have higher testosterone levels than partnered males and that higher testosterone levels are associated with stronger smelling BO, the current study aimed to determine if, by extension of previous findings, single males’ BO smells stronger than partnered males’ BO. Eighty-two heterosexual women aged 18–35 years rated the BO and faces of six different males also aged 18–35 years. Consistent with the hypothesis, single men’s BO smelled stronger than partnered men’s BO and single men’s faces were rated as more masculine than partnered men’s faces. The possible advantages of females being able to identify single males are addressed in the Discussion.

Fatal attraction: lone star ticks (Amblyomma americanum) exhibit preference for human female breath over male breath

Ticks use a variety of chemical cues to locate hosts, the main cue being carbon dioxide, which is exhaled by hosts. This study sought to experimentally determine whether ticks exhibit preference among human hosts based on host sex, as the chemical components of human male and female breath have been shown to differ. We focused on the lone star tick, Amblyomma americanum, due to its importance as a disease vector in the United States and its active host-seeking behavior. To test the hypothesis that ticks exhibit preference based upon host sex, we conducted a binary choice behavioral bioassay. Male and female human volunteers (n = 20 pairs) breathed into opposite sides of a secured polycarbonate tube containing 10 adult A. americanum and the proportion of ticks that exhibited a host preference was recorded. We found that under controlled conditions, human females attract a significantly larger proportion of ticks than males. Possible mechanisms to explain these results include that (1) female breath contains components that ticks find attractive, and/or (2) male breath contains a repellent chemical component.

Reconciling Not Eating Meat and Masculinity in the Marketing Discourse for New Food Alternatives

Traditional hegemonic masculinity can be traced on the typical man's plate where meat represents the centerpiece. Meat consumption dominates the current marketing discourse which builds on masculinity to reinforce the stereotyped gender-based diets. In light of scientific evidence about the detrimental impacts of meat consumption on human wellbeing and environmental health, this chapter argues that men are at the crossroads where the concept of masculinity is being redefined. Their social role is similarly changing with new expectations for more sustainable diets which call for plant-based food choices and possibly lab-grown meat. Some men are endorsing these imperatives while others continue to succumb to social inertia. A new marketing discourse is needed which reconciles masculinity with not eating meat and encourages a transition to alternative dietary choices that are better for personal health, allow improved use of the planet's resources, and have less impact on climate change.

Impact of Consumption of Bananas on Attraction of Anopheles stephensi to Humans

Humans vary in attractiveness to mosquitoes, a phenomenon that is largely attributed to differences in physical cues such as heat and volatile odors emanating from breath and skin. Diet can change human odors but whether specific dietary components alter host attractiveness is largely unexplored. We identified bananas as a target for study following a survey of the internet for advice on avoiding mosquito bites. Human attractiveness to Anopheles stephensi Liston was measured using a glass vial bioassay where mosquito contacts were measured before and 1–3 h after ingestion of bananas or grapes. Consumption of grapes had no effect on the number of contacts but banana ingestion resulted in a significant increase in the overall number of contacts in spite of individual variation that included some subjects who showed no effect or decreases in contacts. Further tests with a single volunteer showed that the effect was repeatable and consistent across 15 trials. The magnitude of the increase was not affected by the number of bananas eaten. Increased contact counts after banana ingestion were also observed when A. gambiae Giles was tested. These results support the hypothesis that diet plays an important role in mediating host attractiveness to anopheline mosquitoes.

Comparing the sniffing behavior of great apes

The importance of smell in humans is well established but we know little about it in regard to our closest relatives, the great apes, as systematic studies on their olfactory behavior are still lacking. Olfaction has long been considered to be of lesser importance in hominids given their relatively smaller olfactory bulbs, fewer functional olfactory receptor genes than other species and absence of a functional vomeronasal organ. Therefore, the aim of this study was to evaluate the use of olfaction in hominids. In particular, we observed sniffing behavior in captive groups of four species (Sumatran orangutans, Pongo abelii; Western lowland gorillas, Gorilla gorilla gorilla; Western chimpanzees, Pan troglodytes verus; bonobos, Pan paniscus) and evaluated in which contexts sniffing was used. Our results show that all investigated species frequently used the sense of smell, and that the sniffing frequency varied with species, sex, age, and context. Most sniffing events were observed in gorillas in comparison to the three other species. Sniffing frequencies were also influenced by sex, with males sniffing slightly more often than females. Furthermore, our results revealed an effect of age, with younger individuals sniffing more often than older individuals. All species mainly sniffed in the non-social context (i.e., toward food and other environmental items) rather than in the social context (i.e., at conspecifics), suggesting that the evaluation of the environment and the nutritional value of food items is of major importance to all great ape species investigated here. In contrast to the other species and female chimpanzees, however, male chimpanzees most often used olfaction to inspect their conspecifics. Together, our study suggests that olfaction is likely to be more important in great apes than previously appreciated.

Influence of Body Odors and Gender on Perceived Genital Arousal

Olfaction is often linked to mating behavior in nonhumans. Additionally, studies in mating behavior have shown that women seem to be more affected by odor cues than men. However, the relationship between odor cues and sexual response-specifically, sexual arousal-has not been studied yet. The aim of this study was to evaluate the impact of the exposure to human body odors (from individuals of the opposite gender) on perceived genital arousal, while these were presented concomitantly to sexually explicit video clips. Eighty university students (40 women) rated their perceived genital arousal (perceived degree of erection/genital lubrication) in response to an audiovisual sexual stimulus, while simultaneously exposed to a body odor from an opposite-gender donor or no odor. Participants also rated each odor sample's (body odor and no odor) perceived pleasantness, intensity, and familiarity. Findings indicated that odor condition had an effect on women's (but not men's) perceived genital arousal, with women showing higher levels of perceived genital arousal in the no odor condition. Also, results showed that women rated body odors as less pleasant than no odor. Notwithstanding, the odor ratings do not seem to explain the association between body odor and perceived genital arousal. The current results support the hypothesis that women, rather than men, are sensitive to odors in the context of sexual response. The findings of this study have relevance for the understanding of human sexuality with respect to chemosensory communication.

What Is More Important

The unnecessary question what a man is without his masculinity, is deeply ingrained into the socially established norms of strength, power, virility and machoism. Although the traditional male masculinity stereotype and its association with meat consumption are still undisputable for many “real” men, there is indication about a shift toward a new modern evolutionary masculinity which reflects more sustainability values. The chapter explores this based on a survey of Sydney men. It reveals the influence of new factors, such as environmental, health and animal welfare concerns, which shape the concept of the masculine. Meat-eating men will experience increasing pressure to defend their traditional masculinity. The Sydney study also explores the factors likely to influence Australian men to replace a meat-centred diet with more plant-based alternatives.

Smelling is Telling: Human Olfactory Cues Influence Social Judgments in Semi-Realistic Interactions

How does a person's smell affect others' impressions of them? Most body odor research asks perceivers to make social judgments based on armpit sweat without perfume or deodorant, presented on t-shirts. Yet, in real life, perceivers encounter fragranced body odor, on whole bodies. Our "raters" wore blindfolds and earplugs and repeatedly smelled same-sex "donors" in live interactions. In one condition, donors wore their normal deodorant and perfume ("diplomatic" odor) while in the other condition, donors were asked to avoid all outside fragrance influences ("natural" odor). We assessed the reliability of social judgments based on such live interactions, and the relationships between live judgments and traditional t-shirt based judgments, and between natural- and diplomatic odor-based judgments. Raters' repeated live social judgments (e.g., friendliness, likeability) were highly consistent for both diplomatic and natural odor, and converged with judgments based on t-shirts. However, social judgments based on natural odor did not consistently predict social judgments based on diplomatic odor, suggesting that natural and diplomatic body odor may convey different types of social information. Our results provide evidence that individuals can perceive reliable, meaningful social olfactory signals from whole bodies, at social distances, regardless of the presence or absence of perfume. Importantly, however, the social value of these signals is modified by the addition of exogenous fragrances. Further, our focus on judgments in same-sex dyads suggests that these olfactory cues hold social value in non-mating contexts. We suggest that future research employ more ecologically relevant methods.

Changes in diet associated with cancer: An evolutionary perspective

Changes in diet are frequently correlated with the occurrence and progression of malignant tumors (i.e., cancer) in both humans and other animals, but an integrated conceptual framework to interpret these changes still needs to be developed. Our aim is to provide a new perspective on dietary changes in tumor‐bearing individuals by adapting concepts from parasitology. Dietary changes may occur alongside tumor progression for several reasons: (i) as a pathological side effect with no adaptive value, (ii) as the result of self‐medication by the host to eradicate the tumor and/or to slow down its progression, (iii) as a result of host manipulation by the tumor that benefits its progression, and finally (iv) as a host tolerance strategy, to alleviate and repair damages caused by tumor progression. Surprisingly, this tolerance strategy can be beneficial for the host even if diet changes are beneficial to tumor progression, provided that cancer‐induced death occurs sufficiently late (i.e., when natural selection is weak). We argue that more data and a unifying evolutionary framework, especially during the early stages of tumorigenesis, are needed to understand the links between changes in diet and tumor progression. We argue that a focus on dietary changes accompanying tumor progression can offer novel preventive and therapeutic strategies against cancer.