Fig. 3

a. The barrier functions of the skin are performed by the lipids present in the outermost layer of the skin, the stratum corneum (adapted from Traversier et al. 2018). b. The application and target of cosmetic products on the outer layers of skin. The diagram shows the probable routes of transport of therapeutic products through the skin (a) intercellular through lipid bilayers, (b) transcellular through keratinocytes (c) shunt through hair follicles and sweat glands. The stratum corneum (SC) is the outermost layer of the skin consisting of mostly dead skin cells is a major barrier to harmful substances, and the epidermis is the major outer thin layer of skin (adapted and modified from Zakrewsky et al. 2015 with permission)