In cosmetics, the important thing is to maintain healthy skin and enjoy a comfortable life both physically and mentally. One example of healthy skin is “soft skin” that is less prone to wrinkles. Key ingredients for maintaining skin softness are moisturizers and oils, and self-organizing structures (α-gel) formed by emulsification technology using surfactants and higher alcohols have long been utilized for stable formulation. To make the skin softness pronounced enough to potentially improve wrinkles, it is necessary to include moisturizers and emollient oils in much higher concentrations than in conventional formulations. However, there is a trade-off, as this significantly reduces the product's usability and emulsification stability. This article introduces the characteristics of α-gel, which forms the backbone of emulsification, and discusses the features of a newly developed α-gel inspired by the structure of intercellular lipids in the stratum corneum, along with its formulation applications, based on research findings.

The establishment of human keratinocyte culture techniques and the successful transplantation of cultured epidermal autografts greatly advanced human epidermal keratinocyte stem cell research. Experimental evidence first demonstrated the presence of stem cells within the keratinocyte population, followed by the identification of diverse cell surface markers characteristic of keratinocyte stem cells. In addition, multiple models—driven by advances in research methodolo­gies—have been proposed to explain how keratinocyte stem cells located in the basal layer of the epidermis maintain epidermal homeostasis, a subject that continues to be actively debated. Furthermore, this research field has been applied to gene therapy for congenital epidermal disorders by combining cultured epidermal autografts with genetic modification of keratinocyte stem cells. This review outlines how studies on human keratinocyte stem cells have contributed to the conceptual development of the stem cell system and to elucidating the mechanisms by which stem cells maintain tissue homeostasis.

Facial cleansers are expected to have psychological benefits such as a refreshing effect in addition to the functional aspect of keeping the skin clean. Facial cleansers are required to have functionality, safety, and a comfortable feeling when used. In particular, the “sappari” feeling, which means a sense of cleanliness and comfort, is an important factor in the refreshing effect of face washing. In this study, we used the evaluation grid method to extract a qualitative evaluation structure regarding the feeling of using a facial cleanser and clarified the factors that determine the “sappari” feeling when using a facial cleanser. Furthermore, to clarify the causal relationship between the factors extracted by the evaluation grid method and the “sappari” feeling, we performed an analysis using structural equation modeling. As a result, it was revealed that the “sappari” feeling is mainly formed by the “dirt removal feeling” and the “cool feeling”. In addition, it was shown that although the “foam quality” does not directly affect the “sappari” feeling, it indirectly contributes to it through the “dirt removal feeling”. The results of this study will contribute to the design of a facial cleanser with a comfortable feeling that is excellent in the “sappari” feeling, and will lead to the development of a facial cleanser that contributes to improving the quality of life, such as mental stability and stress reduction through the refreshing effect.

In beauty salons, a hair treatment technique is used in which hair that has had a treatment applied to it is rubbed with the hands in the hope of enhancing the effect of the rinse-off hair treatment. Sensory evaluation of the process of rubbing treatment into hair confirmed a reduction in hair waviness and an improvement in the overall silhouette. To elucidate the mechanism behind this waviness reduction effect, we investigated the dyeing behavior and penetration region of basic red 51, which was incorporated into the treatment as a marker. Furthermore, we examined the structural changes in non-keratin protein aggregates and the accompanying changes in physical properties. The results showed that the treatment rubbing operation 1) increased the volume and area of penetration of basic red 51 dye used as a marker, 2) changed the hair into a uniform and flexible material, 3) reduced the distortion caused by rearrangement of the non-keratin protein aggregate structure during the blow-drying operation while straightening wet hair and made the cohesive structure more uniform. The treatment rubbing operation relaxes the non-keratin protein aggregates in the hair while increasing the penetration area of the treatment ingredients into the hair. Subsequently, during any blow-drying operation while the hair is straightened, the loosened non-keratin protein aggregates tend to rearrange more uniformly along the fiber axis, leading to a reduction in hair waviness.