Percutaneous penetration of active cosmetics ingredients

This article presents the science output regarding percutaneous transport mechanisms, penetration promotors and the methods of active substances skin absorption enhancement. The interaction between cosmetic ingredient and skin cells determines efficiency of the product. The study presents the most important functions of the skin outlayer (stratum corneum), its structure (Fig. 1) and permeability [1–7]. Due to the compact structure, stratum corneum prevents skin water loss. Moreover, it protects human body from outer substances influence [8–12]. Relationship between compound properties and its ability to skin absorption was also described. Physicochemical properties like lipophilicity, compound structure and particle size have a significant influence on intensity of the compounds skin penetration [4, 16–25]. Lipophilicity of a molecule is defined using many theoretical and experimental methods which allow to predict cosmetic ingredients assimilation [26–42]. Moreover, cosmetic base composition [43–47] and the presence of the penetration enhancers (promotors) also affect active ingredients absorption through the skin [48–49]. The most popular equipment used for testing the absorption and the penetration of active substances through the human skin are described in the last part of the manuscript. Compounds permeability through the skin could be tested using various experimental methods [50–58] including the diffusion cells equipped with membranes or prepared skin fragments [37, 55, 64–67]. The most common used are Franz diffusion cells (Fig. 4) and flow diffusion cell (Fig. 5). The measurement of permeation through stratum corneum using ATR -FTIR method is quite reliable and simple (Fig. 8), although measuring skin penetration is made by Saarbrucken penetration model (Fig. 6) and by application of Tape Stripping technique (Fig. 7). The study of skin absorption mechanisms and factors influencing this process is a great opportunity to design efficient cosmetic recipes and a possibility to make more effective, active cosmetic ingredients