4. Fate after cutaneous administration

4.1 A reminder of skin physiology

The skin is made up of 3 superimposed tissues (figure 7 ). The outermost, the epidermis, is made up of the stratum corneum, a stratified keratinized squamous epithelium in perpetual renewal, and the deeper stratum germinativum, which contains the cells that will eventually form the stratum corneum. The epidermis provides mechanical and biochemical protection, and is the first barrier for drugs administered to the skin. The second, looser layer is the dermis. This tissue contains blood vessels and connective tissue, facilitating the diffusion of molecules. The deepest, the hypodermis, contains connective tissue as well as...