Human body odor is colorless, transparent, and intangible, making it perceptible to animals, including humans, through the sense of smell rather than vision. In the natural world, body odor, manifested through pheromones, plays a crucial role as a communication tool for inter-species interactions, such as territorial behavior and mate selection, among wildlife. On the other hand, body odor in humans is generally associated with an unpleasant smell that creates a negative impression. Another olfactory aspect emanating from humans, namely bad breath or halitosis, can elicit particularly strong discomfort in close face-to-face encounters. Body odor and bad breath are challenging for individuals to self-identify, with many being unaware of their own strong odor, which can negatively impact interpersonal relationships. Conversely, some individuals experience olfactory reference syndrome, wherein they harbor excessive fear or anxiety about their own body odor. Addressing these concerns requires the development of effective methods for evaluating and analyzing body odor and bad breath, understanding the factors contributing to their occurrence, and proposing appropriate solutions. This paper discusses the mechanisms underlying the generation of body odor and bad breath, incorporating the research findings, and delves into the development of novel deodorizing materials to address these olfactory challenges.

Due to continuous global warming and changes in the atmosphere of the Earth, we are facing harsher environments such as high temperatures and exposure to excessive UV radiation. The increase of UV damage is known to adversely affect the human body, necessitating improved protection methods against it. Among available resources on the Earth's surface, we focused on temperature, which is continually increasing, closely synchronized to UV radiation on Earth. We developed a technology that considerably improves UV protection by exposure to high temperature by combining UV absorbers with polyoxyethylene/polyoxypropylene-9/2 dimethyl ether (PPDE). To elucidate the mechanism, in silico experiments were performed using ethylhexyl methoxycinnamate (EHMC), a model UV absorber with particularly high UV protective effect at elevated temperatures. The results indicated that a part of EHMC molecules form a dimer structure at 20℃, imparting low UV protection, and the molecule dissociates into a monomer structure at 40℃, providing a high UV protective effect. The PPDE-EHMC combination reduces the molecular motion at 20℃, allowing maintenance of the monomer structure, and prolongs the UV protective effect, which result matches in vitro results. Through this research, it was found that the UV absorbers used for many years are in the dimeric state, which has low protection effect at room temperature, but are converted to monomers under high temperature, resulting in higher UV protection. Importantly, we also discovered that PPDE acts as a novel factor which contributes to providing a higher UV protection, and its addition is key to maintaining that high protective state of UV absorbers even when returned to room temperature. This result provides an effective strategy for improved skin protection from UV radiation under the scorching sun and contributes to maximizing the UV protective effect with this newly developed sunscreen.

The study aimed to examine the relationship between age-related curved hair, commonly known as“yugami hair”， and the act of repeatedly stretching the hair, which is a common daily hair grooming practice that causes styling difficulties. Firstly, we conducted a survey on the hair care behavior of individuals with yugami hair, which revealed that although they repeatedly combed their hair to prevent undulations and unruly hair, they still found it less manageable. Subsequently, straight and yugami hair samples were obtained based on morphological parameters, followed by cyclical extension conducted under conditions of load stress that are commonly encountered in daily life. Our results indicate a significant increase in the average curvature of yugami hair, which implies that a reduction in the structural stability of intermediate filaments, the protein found within hair, may be a contributing factor. Furthermore, we identified PPG-2 arginine as a component that can suppress the shape and structural changes of yugami hair.

There are some concerns that hypochlorous acid, referred to as residual chlorine hereafter, in tap water causes adverse effects on the human body, especially the skin, due to its strong oxidizing power. However, this detail is still unclear. Therefore, we conducted this study to identify the adverse actions of residual chlorine present in tap water and the effectiveness of purified water focusing on protein carbonylation of corneocytes in the stratum corneum that is correlated with lowered skin moisture functions. An ex vivo examination revealed that the exposure of corneocytes collected by tape-stripping to water containing residual chlorine (residual chlorine water) showed higher protein carbonylation. Additionally, the protein carbonylation promptly progressed after exposure to residual chlorine water. In vivo examination-reproduced situations of the real usage, residual chlorine water increased protein carbonylation of corneocytes. Particularly, the repetition of hand-washing with residual chlorine water increased the value of transepidermal water loss significantly along with higher protein carbonylation of corneocytes. The results suggested that the daily usage of tap water containing residual chlorine could cause protein carbonylation of corneocytes and eventually decrease the epidermal barrier function. The results might indicate a potential action of tap water on people who do not habitually use purified water for body washing. Therefore, this study proposes the possibility that the daily use of purified water instead of tap water could maintain skin health by reducing oxidative damage to corneocytes.

We previously reported that zinc in the cuticle of hair contributes to hair stiffness, and the agedependent decrease in zinc is one of the reasons for the reduction in hair stiffness. From the results, we speculated that the decrease of zinc in the cuticle with aging may be caused by a decline of proteins that retain zinc in the cuticle. We extracted proteins from hair cuticle and analyzed them by mass spectrometry, revealing transglutaminase 3 (TG3) as a zinc-retaining candidate protein. The binding of TG3 to zinc was confirmed using a size fractionation column followed by ICP-MS, and the immunostaining of longitudinal sections of hair root demonstrated the presence of significant amounts of TG3 in the cuticle. Furthermore, hairs from volunteers of various ages were analyzed for the expression of TG3 mRNA in the hair roots, showing a downturn trend of the expression after their 40s and beyond. Based on the results, we concluded that the decrease of zinc in hair with aging past one's 40s is partly due to the decline of the TG3 expression that could retain zinc. In the future, the use of compounds that induce TG3 expression, could become a novel solution to maintain, or even regain hair firmness, resulting from the prevention of zinc loss with aging.

We have developed a fermentation liquid based on germinated brown rice, which has a high nutritional value, using the yeast Lachancea thermotolerans. The fermented liquid is known to be beneficial to the skin and to contain amino acids, but little is known about its other components. Metabolomics is the study of small molecules and has been used in the pharmaceutical and food industries to identify metabolic changes. We used a metabolomics approach to comprehensively analyze the fermentation liquid, determine the components of the fermentation, and correlate them with functionality for the skin. Acetylpolyamines were identified as a characteristic metabolite of the fermentation liquid. An in vitro evaluation of the efficacy of polyamines and their derivatives, acetylpolyamines, confirmed that they promoted hyaluronic acid production in the epidermis and dermis, inhibited melanin production, and promoted glutathione production. Next, the permeability of acetylpolyamines and polyamines was evaluated using a three-dimensional human epidermis experimental model. Polyamines and acetylpolyamines penetrated to the lower part of the cornified layer in 1 h, whereas the permeability of the granular layer differed among acetylpolyamines. Using a three-dimensional human epidermis model, hyaluronic acid production around the basement membrane induced by permeating spermidine trihydrochloride and N⁸-Acetylspermidine dihydrochloride was confirmed. Using a metabolomics approach, we have contributed to a better understanding of the active compounds present in fermented liquids that can be used for skin wellness.

Hair thinning and loss cause the deterioration of quality of life by affecting the mental state of a person and even the impression of others about them. Although various medications have been developed to treat these conditions, people still prefer hair tonics because of the absence of side effects. To address this need, a hair tonic has been formulated containing a royal jelly（RJ） extract to hydrate the scalp. The incorporation of honeybee-produced RJ extract was fostered by its reputation as a moisturizing agent. A clinical trial has been conducted to prove the ability of RJ-based hair tonic to stimulate growth. The trial revealed an increase in the hair number, the anagen ratio, and the moisture content in the stratum corneum of the scalp, as well as the improvement of the scalp and hair quality based on a subjective evaluation. Nevertheless, since the hair tonic formula contains other medicinal ingredients besides the RJ extract, the effect of this latter on hair growth is unclear. For that reason, the gene expression in dermal papilla cells after using the RJ extract was examined, and showed that the addition of this ingredient leads to an increase in the expression levels of IGF-1 and FGF-7, responsible for maintaining the anagen. Therefore, the RJ extractcontaining hair tonic is expected to treat hair thinning and loss and promote hair growth for both genders.