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.

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.

Major histocompatibility complex-associated odour preferences and human mate choice: near and far horizons

The major histocompatibility complex (MHC) is a core part of the adaptive immune system. As in other vertebrate taxa, it may also affect human chemical communication via odour-based mate preferences, with greater attraction towards MHC-dissimilar partners. However, despite some well-known findings, the available evidence is equivocal and made complicated by varied approaches to quantifying human mate choice. To address this, we here conduct comprehensive meta-analyses focusing on studies assessing: (i) genomic mate selection, (ii) relationship satisfaction, (iii) odour preference, and (iv) all studies combined. Analysis of genomic studies reveals no association between MHC-dissimilarity and mate choice in actual couples; however, MHC effects appear to be independent of the genomic background. The effect of MHC-dissimilarity on relationship satisfaction was not significant, and we found evidence for publication bias in studies on this area. There was also no significant association between MHC-dissimilarity and odour preferences. Finally, combining effect sizes from all genomic, relationship satisfaction, odour preference and previous mate choice studies into an overall estimate showed no overall significant effect of MHC-similarity on human mate selection. Based on these findings, we make a set of recommendations for future studies, focusing both on aspects that should be implemented immediately and those that lurk on the far horizon. We need larger samples with greater geographical and cultural diversity that control for genome-wide similarity. We also need more focus on mechanisms of MHC-associated odour preferences and on MHC-associated pregnancy loss. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Body odours as a chemosignal in the mother-child relationship: new insights based on an human leucocyte antigen-genotyped family cohort

Mothers are able to identify the body odour (BO) of their own child and prefer this smell above other BOs. It has hence been assumed that the infantile BO functions as a chemosignal promoting targeted parental care. We tested this hypothesis and examined whether children's BOs signal genetic similarity and developmental status to mothers. In addition, we assessed whether BOs facilitate inbreeding avoidance (Westermarck effect). In a cross-sectional design, N = 164 mothers participated with their biological children (N = 226 children, aged 0-18 years) and evaluated BO probes of their own and four other, sex-matched children. Those varied in age and in genetic similarity, which was assessed by human leucocyte antigen profiling. The study showed not only that mothers identified and preferred their own child's BO, but also that genetic similarity and developmental status are transcribed in BOs. Accordingly, maternal preference of their own child's odour changes throughout development. Our data partly supported the Westermarck effect: mothers' preference of pubertal boys' BOs was negatively related to testosterone for the own son, but not for unfamiliar children. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

People expressing olfactory and visual cues of disease are less liked

For humans, like other social animals, behaviour acts as a first line of defence against pathogens. A key component is the ability to detect subtle perceptual cues of sick conspecifics. The present study assessed the effects of endotoxin-induced olfactory and visual sickness cues on liking, as well as potential involved mechanisms. Seventy-seven participants were exposed to sick and healthy facial pictures and body odours from the same individual in a 2 × 2 factorial design while disgust-related facial electromyography (EMG) was recorded. Following exposure, participants rated their liking of the person presented. In another session, participants also answered questionnaires on perceived vulnerability to disease, disgust sensitivity and health anxiety. Lower ratings of liking were linked to both facial and body odour disease cues as main effects. Disgust, as measured by EMG, did not seem to be the mediating mechanism, but participants who perceived themselves as more prone to disgust, and as more vulnerable to disease, liked presented persons less irrespectively of their health status. Concluding, olfactory and visual sickness cues that appear already a few hours after the experimental induction of systemic inflammation have implications for human sociality and may as such be a part of a behavioural defence against disease. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Bioactive compounds sourced from Terminalia spp. in bacterial malodour prevention: an effective alternative to chemical additives

OBJECTIVE

Recently, our group reported that extracts prepared from the Australian native plant Terminalia ferdinandiana Exell. are potent inhibitors of the growth malodorous bacteria with similar efficacy to triclosan and through these results, we highlighted a potential biological alternative to the current chemical additives. Other members of the genus Terminalia are also well documented for their antibacterial potential and tannin contents and thus were investigated as potential deodorant additives.

METHODS

Solvent extractions prepared from of selected Indian, Australian and South African Terminalia spp. were screened by disc diffusion and liquid dilution assays against C. jeikeium, S. epidermidis, P. acnes and B. linens. The antibacterial activity was quantified by liquid dilution MIC assays. The extracts were screened for toxicity using Atremia franciscana nauplii and HDF cell viability bioassays. High-resolution time-of-flight (TOF) LC-MS and GC-MS headspace fingerprint analysis was used to detect tannin, flavonoid and terpenoid components in the extracts.

RESULTS

Bacterial growth inhibition was observed in all Terminalia extracts with the methanolic T. chebula, T. carpenteriae and T. sericea extracts the most promising bacterial growth inhibitors, yielding MIC values as low as 200 µg mL^-1 . Toxicity analyses of the extracts were favourable, and we determined that the methanolic T. chebula, T. carpenteriae and T. sericea extracts were all non-toxic. Using previously detected T. ferdinandiana antimicrobials as benchmarks, LC-MS and GC-MS fingerprint analyses revealed similar compounds in the methanolic T. chebula, T. carpenteriae and T. sericea extracts.

CONCLUSION

Through these results, we propose that Terminalia spp. extracts may be useful deodorant additives to inhibit the growth of axillary and plantar malodorous bacteria, offering a biological alternative to their chemically synthesized counterparts.

Extracts inhibit the growth of body odour-forming bacteria

OBJECTIVE

Terminalia ferdinandiana extracts are potent growth inhibitors of many bacterial pathogens. They may also inhibit the growth of malodour-producing bacteria and thus be useful deodorant components, although this is yet to be tested.

METHODS

Terminalia ferdinandiana fruit and leaf solvent extracts were investigated by disc diffusion and liquid dilution MIC assays against the most significant bacterial contributors to axillary and plantar malodour formation. Toxicity was determined using the Artemia franciscana nauplii bioassay. Non-targeted HPLC separation of the methanolic leaf extract coupled to high-resolution time-of-flight (TOF) mass spectroscopy was used for the identification and characterization of individual components in the extract.

RESULTS

The T. ferdinandiana leaf extracts were the most potent bacterial growth inhibitors. The leaf methanolic extract was particularly potent, with low MIC values against C. jeikeium (233 μg mL^-1 ), S. epidermidis (220 μg mL^-1 ), P. acnes (625 μg mL^-1 ) and B. linens (523 μg mL^-1 ). The aqueous and ethyl acetate leaf extracts were also potent growth inhibitors of C. jeikeium and S. epidermidis (MICs < 1000 μg mL^-1 ). In comparison, the fruit extracts were substantially less potent antibacterial agents, although still with MIC values indicative of moderate growth inhibitory activity. All T. ferdinandiana leaf extracts were non-toxic in the Artemia franciscana bioassay. Non-biased phytochemical analysis of the methanolic leaf extract revealed the presence of high levels of and high diversity of tannins and high levels of the flavone luteolin.

CONCLUSION

The low toxicity of the T. ferdinandiana leaf extracts and their potent growth inhibition of axillary and plantar malodour-producing bacteria indicate their potential as deodorant components.

Towards a bacterial treatment for armpit malodour

Axillary malodour is a frustrating condition for many people. It can lead to significant discomforts and various psychological effects. The underarm microbiome plays a major role in axillary malodour formation. Not only the bacteria on the epidermis, but also and especially those living in the sweat glands, sweat pores and hair follicles play a pivotal role in malodour development. To treat underarm malodour, this viewpoint article envisions a bacterial treatment. Replacing the autochthonous malodour-causing microbiome with a non-odour-causing microbiome, through an armpit bacterial transplantation or direct application of probiotics/non-odour-causing bacteria, could resolve the condition. Selective steering of the microbiome with prebiotics, biochemicals or plant extracts can likewise greatly help in improving the underarm odour. Elimination/inhibition of the "bad bugs" and application/stimulation of the "good bugs" will be part of the future treatment for axillary body odour.

Effect of Biological Relatedness on Perfume Selection for Others: Preliminary Evidence

People tend to choose perfumes to complement their body odour. As kin share some body odour qualities, their ability to select complementary perfumes for relatives might be higher compared with selection for nonrelatives. We tested this in two studies, comparing selection of a perfume for a target man by himself and by either a familiar but unrelated individual (girlfriend; Study 1) or a relative (sister; Study 2). Target men applied the two perfumes (own or other's choice) to their axillae and then wore cotton pads for 12 hr. Collected perfume-body odour blends and perfumes alone were assessed by rater panels. In Study 1, the blends were rated as nominally more pleasant when body odours were mixed with the perfumes selected by girlfriends compared with those selected by target men themselves. In Study 2, body odours mixed with perfumes selected by sisters were rated significantly more attractive than those mixed with perfumes selected by target men. No significant differences were found for attractiveness and pleasantness ratings when perfumes were rated alone, suggesting that it was the resulting blends that were uniquely different. Our results indicate that sisters might be particularly tuned to select suitable perfumes for their siblings.

Identification of axillary Staphylococcus sp. involved in the production of the malodorous thioalcohol 3-methyl-3-sufanylhexan-1-ol

The production of malodour by humans is mediated by bacterial transformation of naturally secreted, non-odorous molecules. Specifically in the underarm (axilla), malodour arises due to biotransformation by the microbiota of dipeptide-conjugated thioalcohols, particularly S-[1-(2-hydroxyethyl)-1-methylbutyl]-(L)-cysteinylglycine (Cys-Gly-3M3SH). This molecule, secreted by the axilla, has a well-established role in malodour when metabolized to free thioalcohol by bacteria. We present Cys-Gly-3M3SH biotransformation data from a library of skin-isolated corynebacteria and staphylococci and report a significant variation in thioalcohol generation across individual bacterial species. Staphylococcus hominis, Staphylococcus haemolyticus and Staphylococcus lugdunensis were particularly efficient Cys-Gly-3M3SH transformers. In contrast, Staphylococcus epidermidis and Corynebacterium tuberculostearicum, both highly prevalent axillary commensals, are low producers of 3M3SH. We also identify significant differences between the ability of several isolates to biotransform Cys-Gly-3M3SH compared to S-benzyl-L-Cys-Gly, a dipeptide-linked version of a commonly used malodour precursor substrate. Finally, using traditional biochemical assays we subsequently establish that Cys-Gly-3M3SH is actively transported into S. hominis, rather than passively diffusing across the membrane. This work significantly enhances our knowledge of Cys-Gly-3M3SH biotransformation by physiologically important bacteria in the axillary microbiota.