Applied Cosmetic Science and Technology Applied Cosmetic Science and Technology

Percutaneous absorption and skin permeation of cosmetics and their ingredients are reviewed. In this field, the definitions of related terms are often vague, and researchers sometimes use different terms. Thus, the definitions are first clarified for these terms. Next, examples of active ingredients in current medicated cosmetics in Japan are presented, for which percutaneous absorption and skin penetration are essential. Then, the skin barrier properties, especially in the stratum corneum, are summarized, and the skin penetration and permeation behaviors are explained for chemical compounds containing cosmetic ingredients. The skin permeation kinetics are also mathematically described, and factors affecting these kinetics are listed, such as lipophilicity, molecular weight, and thermodynamic activity of chemical compounds. After that, in vitro and in vivo methods for measuring skin permeability are exemplified, and finally, the future image of cosmetics and quasi-pharmaceutical products is summarized, including reader’s expectations.