The appearance of skin is one of the critical research targets in cosmetology since cosmetics are key items for improving or controlling skin appearance. Therefore, a lot of studies on skin appearance have been carried out for the development of cosmetics. Such previous cosmetic studies are roughly subdivided into several approaches: psychology-based, optics-based, and image-based ones. An approach based on visual information processing is also important, especially when the mechanism of the appearance perception is investigated. In these approaches, the optics-based one has the advantage of identifying the skin optical properties (e.g. reflection, translucency, and spectral properties) that relate to the features of the targeted appearance. The image-based approach has the advantage of identifying visual cues that induce the features of the targeted appearance. Since such optical properties and visual cues are crucial information for designing formulations and ingredients of cosmetics, studies on the skin appearance based on optics and image have been frequently carried out. In this paper, to begin with, the above-mentioned approaches are overviewed. Then, more details regarding the optics-based and image-based approaches are argued. Finally, some of the previous studies on the development of cosmetic ingredients for controlling the skin appearance, which employed optics- and image-based approaches, are reviewed.

The loop-mediated isothermal amplification (LAMP) method can be expected to shorten the time required to detect specific micro-organisms in cosmetic products by the microbial limit test. However, the LAMP reaction failed to detect Candida albicans when test samples were contaminated with this species and other bacteria. This was because the concentration of C. albicans (a kind of yeast) did not exceed the detection limit due to inhibition by the growth of other bacteria in pre-culture medium. To solve this problem, we improved the pre-culture conditions to promote the growth of C. albicans. We also found that the dilution step in the LAMP protocol could be omitted and the precise detection of C. albicans be achieved by the LAMP method for almost all cosmetic products.

It is widely-accepted that maintaining the scalp in a good condition is important for growing healthy hair. However, no adequate evidence is available that shows how scalp conditions affect physical properties of hair. From the observation of 101 Japanese women's scalp condition, here we found that the severer the scalp problem is, the more sebum is secreted, and moreover, the less resilient the hairs are. Based on these results, we hypothesized that irritants derived from secreted sebum cause scalp problems accompanied by the release of inflammatory factors, which affect hair follicular cells and suppress expression of genes essential to healthy hair formation. To address this hypothesis, we employed human hair follicle cell cultures. In outer root sheath cells, lipid peroxide up-regulated inflammatory cytokines such as IL-1 and IL-8, which suppressed keratin-associated protein 5.1 (KAP5.1) in hair organ cultures. KAP5.1 is known as a key molecule for cuticle strength. Furthermore, in several plant extracts we found an inhibitory effect on the increase of inflammatory cytokines caused by lipid peroxide. Taken together, it is suggested that increased inflammatory factors associated with scalp problems—at least those due to sebumderived irritants—act on hair follicle cells to deteriorate hair formation by down-regulating gene expression of key molecules, resulting in attenuation of the tensile strength and resilience of newly formed hair fibers. This consequence can be prevented with several plant extracts by suppressing the increase in inflammatory cytokines at the first step.

An increased awareness regarding the negative effects of ultraviolet (UV) rays on the skin has led to an increase in the use of sunscreen; two types of sunscreen—non-chemical and chemical—are present in the market. The non-chemical type has the characteristics of water resistance and safety but is difficult to remove via ordinary cleansing; thus, special cleansing agents are needed to remove sunscreen from the skin. On the other hand, the chemical type has the characteristics of washability and good texture although this type raises concern about skin irritation, depending on skin type. In this work, a sunscreen having sufficient water resistance and excellent washability was developed by optimizing the combination of inorganic UV scattering agents (IUVSAs) and inorganic UV scattering agent dispersants. First, we paid attention to the IUVSAs treated with an N-acyl amino acid having both hydrophobic and hydrophilic groups. In addition, we studied combinations of IUVSAs and the various dispersants. Finally, we developed a sunscreen having sufficient water resistance and excellent washability by using the IUVSAs treated with the N-acyl amino acid and specific dispersants.