Scientific Descriptions of the Skin

The skin has protective functions against all exogenous noxae and regulates temperature, water, and salt balance. In addition, the skin also secures the organism by perceiving external stimuli such as temperature, touch, pain, pleasure, and pressure. It is very complex and divided from the inside out into three sections: subcutis, dermis, and epidermis. The inner layer of the epidermis represents the stratum basale, where the new skin cells are formed. The top layer, the stratum corneum, consists of dead horny cells, the corneocytes, and an acid mantle, which together form the skin barrier. Many active ingredients work advantageously in the skin to overcome the barrier. There are four options for this. Certain lipophilic substances penetrate the skin through the lipid matrix between the corneocytes, while amphiphilic water-soluble ingredients can overcome the barrier via the corneodesmosomal pathway. Molecular size and composition as well as the spatial structure limit the penetration rate. Hydrophilic substances can be introduced into the skin after chemical modification and via carrier systems (e.g. liposomes). A good cream uses the pathways into the skin for high effectiveness, such as for substances reducing the visible signs of aging.