Applied Cosmetic Science and Technology Applied Cosmetic Science and Technology

In the human stratum corneum, there are a variety of structures that can be observed by X-ray diffraction measurements. Based on these results and those obtained from other complementary techniques, the mechanism of effect upon applying cosmetic ingredients and related substances can be analyzed at the molecular level. Water is a fundamental substance in the stratum corneum. From the X-ray diffraction measurements, it was revealed that normal water content distribution is an important concept to maintain healthy skin. In addition, time-resolved X-ray diffraction measurements showed that glycerol can maintain the normal water content distribution for extended periods of time. The time-resolved methods solved various problems in investigating the effects of cosmetic ingredients. It was demonstrated that sodium dodecyl sulfate disrupted the long-period lamellar structure, and based on this result, the disrupted long-period lamellar structure could be restored by applying a mixture containing acylceramide. In addition, it was observed that the structures formed by the intercellular lipids are characteristically modified according to the ethanol application process, and from analyzing the results, it was suggested that the intercellular lipid matrix is composed of a large amount of a disordered hydrocarbon-chain packing state and that only the disordered state is dissolved by ethanol. Then, it was pointed out that this disordered state, with an average molecular weight of approximately 500 Da, plays an important role in the penetration of cosmetic ingredients into the intercellular lipid matrix. Nanoparticles consisting of lipids suspended in aqueous solution have attracted attention, and the use of time-resolved methods suggests that there exists a mechanism by which nanoparticles are reorganized on the surface of the stratum corneum and effective molecules are released into the stratum corneum.