Thermal infrared directs host-seeking behaviour in Aedes aegypti mosquitoes.

Mosquito-borne diseases affect hundreds of millions of people annually and disproportionately impact the developing world1,2. One mosquito species, Aedes aegypti, is a primary vector of viruses that cause dengue, yellow fever and Zika. The attraction of Ae. aegypti female mosquitos to humans requires integrating multiple cues, including CO2 from breath, organic odours from skin and visual cues, all sensed at mid and long ranges, and other cues sensed at very close range3-6. Here we identify a cue that Ae. aegypti use as part of their sensory arsenal to find humans. We demonstrate that Ae. aegypti sense the infrared (IR) radiation emanating from their targets and use this information in combination with other cues for highly effective mid-range navigation. Detection of thermal IR requires the heat-activated channel TRPA1, which is expressed in neurons at the tip of the antenna. Two opsins are co-expressed with TRPA1 in these neurons and promote the detection of lower IR intensities. We propose that radiant energy causes local heating at the end of the antenna, thereby activating temperature-sensitive receptors in thermosensory neurons. The realization that thermal IR radiation is an outstanding mid-range directional cue expands our understanding as to how mosquitoes are exquisitely effective in locating hosts.

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.

Influence of the human body odor compound HMHA on face perception.

Body odors convey information about the individuals, but the mechanisms are not fully understood yet. As far as human reproduction is concerned, molecules that are produced in sexually dimorphic amounts could be possible chemosignals. 3-hydroxy-3-methylhexanoic acid (HMHA) is one of them-more typical of men. Here, we investigated the possibility that the perception of gender and attractiveness in human faces could be implicitly influenced by this compound. Clearly feminine, ambiguous and clearly masculine faces were primed with an odor of HMHA, a control odor or air. Based on 100-ms face presentation, 40 raters had to identify the face's gender as quickly as possible and provide attractiveness evaluations. 3-hydroxy-3-methylhexanoic acid tended to be perceived as less pleasant and induced lower sniff duration in women compared with men. As to the effects of HMHA on face perception (vs. control conditions), we found that gender identification and the associated response time were unaffected by HMHA. Attractiveness of the faces, however, increased in presence of HMHA, but not in a sex-specific manner and only for unattractive faces with ambiguous gender. In sum, this study found no evidence in favor of a possible role of this sexually dimorphic compound in intrasexual competition nor in intersexual attraction.

An electronic nose can identify humans by the smell of their ear.

Terrestrial mammals identify conspecifics by body odor. Dogs can also identify humans by body odor, and in some instances, humans can identify other humans by body odor as well. Despite the potential for a powerful biometric tool, smell has not been systematically used for this purpose. A question arising in the application of smell to biometrics is which bodily odor source should we measure. Breath is an obvious candidate, but the associated humidity can challenge many sensing devices. The armpit is also a candidate source, but it is often doused in cosmetics. Here, we test the hypothesis that the ear may provide an effective source for odor-based biometrics. The inside of the ear has relatively constant humidity, cosmetics are not typically applied inside the ear, and critically, ears contain cerumen, a potent source of volatiles. We used an electronic nose to identify 12 individuals within and across days, using samples from the armpit, lower back, and ear. In an identification setting where chance was 8.33% (1 of 12), we found that we could identify a person by the smell of their ear within a day at up to ~87% accuracy (~10 of 12, binomial P < 10-5), and across days at up to ~22% accuracy (~3 of 12, binomial P < 0.012). We conclude that humans can indeed be identified from the smell of their ear, but the results did not imply a consistent advantage over other bodily odor sources.

Emotional self-body odors do not influence the access to visual awareness by emotional faces.

A growing body of research suggests that emotional chemosignals in others' body odor (BO), particularly those sampled during fearful states, enhance emotional face perception in conscious and preconscious stages. For instance, emotional faces access visual awareness faster when presented with others' fear BOs. However, the effect of these emotional signals in self-BO, that is, one's own BO, is still neglected in the literature. In the present work, we sought to determine whether emotional self-BOs modify the access to visual awareness of emotional faces. Thirty-eight women underwent a breaking-Continuous Flash Suppression task in which they were asked to detect fearful, happy, and neutral faces, as quickly and accurately as possible, while being exposed to their fear, happiness, and neutral self-BOs. Self-BOs were previously collected and later delivered via an olfactometer, using an event-related design. Results showed a main effect of emotional faces, with happy faces being detected significantly faster than fearful and neutral faces. However, our hypothesis that fear self-BOs would lead to faster emotional face detection was not confirmed, as no effect of emotional self-BOs was found-this was confirmed with Bayesian analysis. Although caution is warranted when interpreting these results, our findings suggest that emotional face perception is not modulated by emotional self-BOs, contrasting with the literature on others' BOs. Further research is needed to understand the role of self-BOs in visual processing and emotion perception.

Investigating Inattentional Blindness Through the Lens of Fear Chemosignals.

Inattentional blindness is a phenomenon wherein people fail to perceive obvious stimuli within their vision, sometimes leading to dramatic consequences. Research on the effects of fear chemosignals suggests that they facilitate receivers' sensory acquisition. We aimed to examine the interplay between these phenomena, investigating whether exposure to fear chemosignals (vs. rest body odors) can reduce the inattentional-blindness handicap. Utilizing a virtual-reality aquarium, we asked participants to count how many morsels a school of fish consumed while two unexpected stimuli swam by. We predicted that participants exposed to fear chemosignals (N = 131) would detect unexpected stimuli significantly more often than participants exposed to rest body odors (N = 125). All participants were adult Portuguese university students aged 18 to 40 years. The results confirmed our hypothesis, χ2(1) = 6.10, p = .014, revealing that exposure to fear chemosignals significantly increased the detection of unexpected stimuli by about 10%. The implications of our findings open a novel avenue for reducing the adverse consequences of inattentional blindness.

Quantification of Anopheles gambiae Olfactory Preferences under Semi-Field Conditions.

Anopheles gambiae is a highly anthropophilic (human-preferring) malaria vector that prefers to blood feed frequently and selectively on humans. This mosquito species exhibits a strong innate olfactory preference to seek out human scent over other animals, and certain humans over others-key behavioral traits with the potential to drive heterogeneity in biting risk and malaria transmission. Here, we describe the application of a large-scale, semi-field system in Zambia for the quantification of An. gambiae olfactory preferences toward whole body odor sourced from individual humans. We detail steps for modifying one-person canvas tents to duct odor from sleeping humans into a central, semi-field flight cage arena that is securely screened. Using this system, we describe a protocol to perform two-choice olfactory preference assays with two human volunteers using laboratory-reared An. gambiae and odor-guided thermotaxis assays that leverage infrared video tracking to quantify mosquito landings on heated targets baited with each body odor sample. This multichoice olfactory preference assay has the potential to be applied with expanded cohorts of humans to define the chemosensory basis of An. gambiae host preference and interindividual differences in human attractiveness to mosquitoes and to be used to quantify the effects of protective measures such as personal and spatial repellents on mosquito landing behavior.

A Behavioral Assay to Quantify Odor-Guided Thermotaxis with Anopheles gambiae under Semi-Field Conditions.

The African malaria mosquito Anopheles gambiae is strongly attracted to human body odor and skin temperature. Quantitative behavioral assays suitable for use in semi-field environments with this nocturnal mosquito species are essential to gain improved insights into An. gambiae sensory biology, the mechanistic basis of mosquito attraction to humans, and host preference. In this protocol, we describe steps for engineering equipment for a novel behavioral assay for An. gambiae, which we have termed the odor-guided thermotaxis assay (OGTA). The OGTA uses infrared videography to quantify landings of female An. gambiae on an aluminum platform heated to human skin temperature that can be baited with volatile odorants such as carbon dioxide or human whole body odor. The OGTA facilitates high-content recordings of An. gambiae landing behavior during odor-guided thermotaxis under naturalistic semi-field conditions without the requirement for domestic power.

Olfactory self-inspection: Own body odour provides cues to one's health and hygiene status.

Olfactory self-inspection has been observed in various mammals, including humans. This behaviour can help individuals to monitor own state, including health and hygiene. This study's aim was to explore the frequency of sniffing particular body parts and investigate possible gender differences. Further, we tested a possible function of this behaviour, namely monitoring health and hygiene, by investigating associations between the frequency of self-sniffing and health, hygiene, and disgust sensitivity. Respondents completed an online survey on self-sniffing behaviour, health status, hygiene habits, and disgust sensitivity. Self-sniffing behaviour was investigated using a purpose-built inventory which explored the incidence and frequency of sniffing different parts of own body. Principal Component Analysis identified three main axes of self-sniffing behaviour: Social acceptability self-inspection, Intimate self-inspection, and Cosmetic self-inspection. Our results further show that respondents with lower standards of hygienic habits engage significantly more in intimate self-inspection (sniffing body parts such as genitals, anus, or navel). Interestingly, individuals who reported more frequent health issues sniff more frequently areas such as the armpits, feet, or own breath (Social acceptability self-inspection), probably to check for possible changes in smell due to illness. Our results indicate that olfactory self-inspection probably has several functions depending on the location from which the smell originates.

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.

Unraveling the universality of chemical fear communication: evidence from behavioral, genetic, and chemical analyses.

Abundant evidence indicates that humans can communicate threat-related information to conspecifics through their body odors. However, prior research has been primarily conducted on Western (WEIRD) samples. In this study, we aimed to investigate whether threat-related information can be transmitted by individuals of East Asian descent who carry a single-nucleotide polymorphism (SNP) 538G → A in the ABCC11 gene, which significantly reduces (noticeable) body odor. To examine this, we recruited 18 self-identified male East Asian AA-homozygotes and 18 self-identified male Western individuals who were carriers of the functional G-allele. We collected samples of their fear-related and neutral body odors. Subsequently, we conducted a double-blind behavioral experiment in which we presented these samples to 69 self-identified female participants of Western Caucasian and East Asian backgrounds. The participants were asked to rate faces that were morphed between expressions of fear and disgust. Notably, despite the "odorless" phenotypical expression of the ABCC11-mutation in East Asians, their fear odor caused a perceptual fear bias in both East Asian and Caucasian receivers. This finding leaves open the possibility of universal fear chemosignaling. Additionally, we conducted exploratory chemical analysis to gain initial insights into the chemical composition of the body odors presented. In a subsequent pre-registered behavioral study (N = 33), we found that exposure to hexadecanoic acid, an abundant compound in the fear and neutral body odor samples, was sufficient to reproduce the observed behavioral effects. While exploratory, these findings provide insight into how specific chemical components can drive chemical fear communication.

Olfactory Cues of Naturally Occurring Systemic Inflammation: A Pilot Study of Seasonal Allergy.

INTRODUCTION: In an attempt to avoid contact with infectious individuals, humans likely respond to generalized rather than specific markers of disease. Humans may thus perceive a noninfectious individual as socially less attractive if they look (e.g., have facial discolouration), move (e.g., have a slower walking pace), or sound (e.g., sneeze) sick. This pilot study tested whether humans are averse to the body odour of noninfectious individuals with a low-grade systemic inflammation. METHODS: We collected the axillary body odour of individuals with severe seasonal allergy (N = 14) and healthy controls (N = 10) during and outside the allergy season and measured serum levels of two inflammatory cytokines (tumour necrosis factor-α and interleukin-5). Independent participants (N = 67) then sampled and rated these odours on intensity and pleasantness. RESULTS: While individuals with seasonal allergy had nominally more unpleasant and intense body odours during the allergy season, relative to outside the allergy season and to healthy controls, these effects were not significant. When examining immune markers, the change in perceived pleasantness of an individual's body odour (from out-to-inside pollen season) was significantly related to the change in their interleukin-5 levels but not to tumour necrosis factor-α. DISCUSSION: Our findings tentatively suggest that the human olfactory system could be sensitive to inflammation as present in a noncommunicable condition. Larger replications are required to determine the role of olfaction in the perception of infectious and noninfectious (e.g., chronic diseases) conditions.

Knockout of OR39 reveals redundancy in the olfactory pathway regulating the acquisition of host seeking in Anopheles coluzzii.

The attraction of anthropophilic mosquitoes to human host cues, such as body odour and carbon dioxide, gradually increases during adult maturation. This acquisition of host-seeking behaviour correlates with age-dependent changes in odorant receptor (OR) transcript abundance and sensitivity of olfactory sensory neurons (OSNs). One OR gene of the human malaria vector, Anopheles coluzzii, AcolOR39, is significantly downregulated in mature females, and a cognate ligand of AcolOR39, sulcatone, a major component of human emanations, mediates the observed behavioural inhibition of newly emerged (teneral) females to human body odour. Knockout of AcolOR39, using CRISPR-Cas9 mutagenesis, selectively abolished sulcatone detection in OSNs, housed in trichoid sensilla. However, knockout of AcolOR39 altered neither the response rate nor the flight behaviour of teneral females in a wind tunnel, indicating the involvement of other genes, and thus a redundancy, in regulating the acquisition of host seeking in mosquitoes.

Human scent as a first-line defense against disease.

Individuals may have a different body odor, when they are sick compared to healthy. In the non-human animal literature, olfactory cues have been shown to predict avoidance of sick individuals. We tested whether the mere experimental activation of the innate immune system in healthy human individuals can make an individuals' body odor be perceived as more aversive (intense, unpleasant, and disgusting). Following an endotoxin injection (lipopolysaccharide; 0.6 ng/kg) that creates a transient systemic inflammation, individuals smelled more unpleasant compared to a placebo group (saline injection). Behavioral and chemical analyses of the body odor samples suggest that the volatile components of samples from "sick" individuals changed qualitatively rather than quantitatively. Our findings support the hypothesis that odor cues of inflammation in axillary sweat are detectable just a few hours after experimental activation of the innate immune system. As such, they may trigger behavioral avoidance, hence constituting a first line of defense against pathogens of infected conspecifics.

Gas-Phase Biosensors (Bio-Sniffers) for Measurement of 2-Nonenal, the Causative Volatile Molecule of Human Aging-Related Body Odor.

The molecule 2-nonenal is renowned as the origin of unpleasant human aging-related body odor that can potentially indicate age-related metabolic changes. Most 2-nonenal measurements rely on chromatographic analytical systems, which pose challenges in terms of daily usage and the ability to track changes in concentration over time. In this study, we have developed liquid- and gas-phase biosensors (bio-sniffers) with the aim of enabling facile and continuous measurement of trans-2-nonenal vapor. Initially, we compared two types of nicotinamide adenine dinucleotide (phosphate) [NAD(P)]-dependent enzymes that have the catalytic ability of trans-2-nonenal: aldehyde dehydrogenase (ALDH) and enone reductase 1 (ER1). The developed sensor quantified the trans-2-nonanal concentration by measuring fluorescence (excitation: 340 nm, emission: 490 nm) emitted from NAD(P)H that was generated or consumed by ALDH or ER1. The ALDH biosensor reacted to a variety of aldehydes including trans-2-nonenal, whereas the ER1 biosensor showed high selectivity. In contrast, the ALDH bio-sniffer showed quantitative characteristics for trans-2-nonenal vapor at a concentration range of 0.4-7.5 ppm (with a theoretical limit of detection (LOD) and limit of quantification (LOQ) of 0.23 and 0.26 ppm, respectively), including a reported concentration (0.85-4.35 ppm), whereas the ER1 bio-sniffer detected only 0.4 and 0.8 ppm. Based on these findings, headspace gas of skin-wiped alcohol-absorbed cotton collected from study participants in their 20s and 50s was measured by the ALDH bio-sniffer. Consequently, age-related differences in signals were observed, suggesting the potential for measuring trans-2-nonenal vapor.

Factors Affecting Postoperative Complications of Suction-Curettage by Arthroscopic Shaver for Bromhidrosis.

BACKGROUND: Suction-curettage by arthroscopic shaver is the most effective treatment for bromhidrosis; however, postoperative complications require wound management and exhibit a high risk of hypertrophic scarring. We investigated factors affecting postoperative complications. METHODS: We retrospectively evaluated data for 215 patients (430 axillae) with bromhidrosis treated with suction-curettage by arthroscopic shaver between 2011 and 2019. Cases followed for less than 1 year were excluded. Complications of hematoma or seroma, epidermis decortication, skin necrosis, and infection were recorded. Multinomial logistic analysis was used to calculate odds ratios and corresponding 95% confidence intervals for the complication of the surgery, adjusting for relevant statistically significant variables. RESULTS: Complications occurred in 52 axillae (12.1%). Epidermis decortication occurred in 24 axillae (5.6%), with a significant difference for age (P < 0.001). Hematoma occurred in 10 axillae (2.3%) with a significant difference in tumescent infiltration use (P = 0.039). Skin necrosis occurred in 16 axillae (3.7%) with a significant difference for age (P = 0.001). Infection occurred in 2 axillae (0.5%). Severe scarring occurred in 15 axillae (3.5%), with complications related to more severe skin scarring (P < 0.05). CONCLUSION: Older age was a risk factor for complications. Use of tumescent infiltration resulted in good postoperative pain control and less hematoma. Patients with complications presented with more severe skin scarring, but none experienced limited range of motion after massage.

Human scent guides mosquito thermotaxis and host selection under naturalistic conditions.

The African malaria mosquito Anopheles gambiae exhibits a strong innate drive to seek out humans in its sensory environment, classically entering homes to land on human skin in the hours flanking midnight. To gain insight into the role that olfactory cues emanating from the human body play in generating this epidemiologically important behavior, we developed a large-scale multi-choice preference assay in Zambia with infrared motion vision under semi-field conditions. We determined that An. gambiae prefers to land on arrayed visual targets warmed to human skin temperature during the nighttime when they are baited with carbon dioxide (CO2) emissions reflective of a large human over background air, body odor from one human over CO2, and the scent of one sleeping human over another. Applying integrative whole body volatilomics to multiple humans tested simultaneously in competition in a six-choice assay, we reveal high attractiveness is associated with whole body odor profiles from humans with increased relative abundances of the volatile carboxylic acids butyric acid, isobutryic acid, and isovaleric acid, and the skin microbe-generated methyl ketone acetoin. Conversely, those least preferred had whole body odor that was depleted of carboxylic acids among other compounds and enriched with the monoterpenoid eucalyptol. Across expansive spatial scales, heated targets without CO2 or whole body odor were minimally or not attractive at all to An. gambiae. These results indicate that human scent acts critically to guide thermotaxis and host selection by this prolific malaria vector as it navigates towards humans, yielding intrinsic heterogeneity in human biting risk.

Body odor disgust sensitivity (BODS) is related to extreme odor valence perception.

Odors are important disease cues, and disgust sensitivity to body odors reflects individual differences in disease avoidance. The body odor disgust sensitivity (BODS) scale provides a rapid and valid assessment of individual differences. Nevertheless, little is known about how individual differences in BODS might correlate with overall odor perception or how it is related to other differences in emotional reactivity (e.g., affect intensity). We investigated how BODS relates to perceptual ratings of pleasant and unpleasant odors. We aggregated data from 4 experiments (total N = 190) that were conducted in our laboratory, and where valence and intensity ratings were collected. Unpleasant odors were body-like (e.g., sweat-like valeric acid), which may provide disease cues. The pleasant odors were, in contrast, often found in soap and cleaning products (e.g., lilac, lemon). Across experiments, we show that individuals with higher BODS levels perceived smells as more highly valenced overall: unpleasant smells were rated as more unpleasant, and pleasant smells were rated as more pleasant. These results suggest that body odor disgust sensitivity is associated with a broader pattern of affect intensity which causes stronger emotional responses to both negative and positive odors. In contrast, BODS levels were not associated with odor intensity perception. Furthermore, disgust sensitivity to odors coming from external sources (e.g., someone else's sweat) was the best predictor of odor valence ratings. The effects were modest in size. The results validate the BODS scale as it is explicitly associated with experimental ratings of odor valence.

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.

Effect of optimizing the use of endoscope on the efficiency of microdynamic bromhidrosis removal operation.

BACKGROUND: Bromhidrosis, also known as body odor, is a common disease in life, which often occurs in young adults. The histological basis of bromhidrosis is the hyperplasia of apocrine sweat glands. OBJECTIVE: To compare the effects of different methods of endoscopy in microdynamic axillary osmidrosis removal on curative effect, complications, and surgical efficiency. METHODS: A total of 149 patients with axillary osmidrosis were treated in our hospital from January 2020 to December 2021. They were treated with endoscopic assistance in the whole process of operation (Group A) and endoscope-assisted exploration after blind rotary cutter suction (Group B), respectively, and the curative effect, complication rate, and surgical efficiency were evaluated. RESULTS: There was no significant difference in the curative effect and complication rate between the two groups, but the endoscope-assisted exploration group after suction with rotary cutter (Group B) had higher surgical efficiency. CONCLUSION: On the basis of professional use of rotary cutter, it is efficient to choose endoscope to check the excision of sweat gland in the operation area and stop bleeding in time after blind suction.