[Physiology of skin pigmentation]

The physiological colour of the skin is due, above all, to the presence of melanin in the dermis and the epidermis, but also to the presence of other pigments of endogenous or exogenous origin, such as iron and carotene. The authors present a study of melanogenesis. They review the structure of the eumelanins and the phaeomelanins and recall the steps in their biosynthesis. They examine the functioning of the epidermal unit of melanization, which is a functional unit consisting of a melanocyte, derived from the neural crest, and the keratinocytes which depend on it. The melanocyte synthetizes pigment granules, the melanosomes, which undergo maturation before being transferred and then broken down by the keratinocytes. Finally, the authors study the principal factors which influence the functioning of the epidermal unit of melanization : genetic control, ultra-violet radiation and endocrine factors.