Pickering emulsion, which stabilizes by adsorbing fine particles to the oil-water interface, is a technology discovered over 100 years ago. Why has it not been used in cosmetic formulations, despite its unique emulsification properties, texture, and stability that differ from conventional surfactant-based emulsification methods? In this review, we explain the basic information you need to know to use it in cosmetics, including the basic emulsification mechanism, the key elements of its stabilization, the selection of the type of oil to control the contact angle, and the preparation method. We then describe L/A (Liquid-in-Air), a system in which droplets are dispersed in air, which is an area that can only be developed using Pickering emulsion. In the second half of the article, we also introduce a development example in which our company applied Pickering emulsion to a sunscreen. This sunscreen was developed as an O/W type sunscreen formulation by emulsifying an oil phase containing a UV absorber using silica, which is a common cosmetic ingredient. As a result, it has become possible to develop a sunscreen formulation that not only continues to protect the skin from UV rays and does not wash away even in the harsh environment of the ocean, but also has the revolutionary effect of using seawater to further enhance the sunscreen's UV protection function.

Skin cell turnover is the process of producing new skin cells to replace existing skin cells. It is known that the turnover speed of skin slows down with aging. On the other hand, cAMP (cyclic adenosine monophosphate) causes various physiological reactions as an intracellular signal transmitter. But its role in the skin, especially in stem cells, which is important for aging, has not been fully elucidated. Therefore, we investigated the relationship between aging and cAMP in epidermal cells. First, we found that the amount of cAMP in adult-derived keratinocytes isolated from older subjects was lower than in neonatal-derived keratinocytes. Next, we checked the effect of cAMP derivative on the skin turnover effect using a three-dimensional skin model. As a result, the thickness of the cAMP derivative was increased. From this, it was considered to be possible that cAMP upregulated improvement of decrease in turnover due to aging. We also found that cAMP in epidermal cells was increased by the addition of caffeine. Furthermore, we developed a liposomal caffeine consisting of single-lamellar liposomes suitable for encapsulation of water-soluble components to improve permeability. From these results, we propose a new approach to prevent the decrease in the function of the epidermal stem cells and the turnover rate of skin with aging with liposomal caffeine.

Sunscreens are developed with various ingredients such as UV absorbers, surfactants and oils. In general, UV absorbers are used in combination and coating films created by these have a significant impact on the final UV protective function. Several imaging methods (e.g., Spectroscopic Imaging and Mass Spectrometry Imaging (MSI)) have been developed for visualizing distribution of UV absorbers. However, conventional methods have a limited ability to evaluate sunscreen coatings in accordance with actual use condition, such as on the skin. In this study, we have developed a new visualization method using MSI and Desorption Ionization Using Through Hole Alumina Membrane (DIUTHAME) to investigate a condition of sunscreens on the skin. As a result, we find DIUTHAME can adsorb sunscreen coatings from the skin keeping its positional information. Moreover, the MSI method can visualize oil-soluble and water-soluble UV absorbers in sunscreen from DIUTHAME absorbed sunscreen coatings. We analyzed UV absorbers contained in sunscreens on the skin by this method. In results of sunscreens with low SPF and PA values, remarkable localization of UV absorbers was observed compared to others with high SPF and PA values. These results suggest the difference in UV protective function is caused by uneven distribution of ingredients on the skin as well as the UV absorbers' content. The established method enables visualization of sunscreen coating on the skin easily, and can contribute to developing innovative sunscreen products.

Hydrogenated Starch Hydrolysate (HSH) is a type of sugar alcohol produced from plant-derived raw materials such as corn. Compared to other sugar alcohols such as sorbitol and xylitol, it is less widely recognized and its utilization value has not been well researched. Against this background, we believe that hydrogenated starch hydrolysate HSH has potential in the field of cosmetics, and have conducted various studies on skin care cosmetics using two types of hydrogenated starch hydrolysate, HSH-1 and HSH-2 with different average molecular weights. In the present study, we conducted a test study using a model skin lotion containing surfactants; hydrogenated starch hydrolysate HSH-2 (average M.W. 1000), which has a large average molecular weight, was found to have decreasing effect on TEWL. While oily raw materials are typical emollients, it is very interesting that TEWL-decreasing effect can be adjusted by HSH with different molecular weights and that such an effect was confirmed with a water-soluble humectants such as hydrogenated starch hydrolysate HSH.