Synthesis and physiological implications of melanic pigments.

The process of melanin synthesis and distribution is called melanogenesis, a process that is based on melanocytes present among the basal cells of the epidermis. Pigments formed in melanocyte melanosomes are then stored in the basal layer of epidermal cells, as well as in dermal macrophages, which become melanophores. From the embryological point of view, melanocytes derive from the melanoblasts of the neural crest, from where they migrate during the first months of life into the skin, eye, cochlea, bone, peripheral nervous system, heart and adipose tissue. The melanic pigments, eumelanin and pheomelanin, are the final product of complex biochemical reactions starting from the amino acid L-tyrosine. Melanin has a major role in skin homeostasis through the photoprotection it offers from the harmful effect of ultraviolet radiation. Melanin absorbs and/or reflects ultraviolet radiation but is also involved in the neutralizing process of free radicals and reactive oxygen species. Pigmentogenesis is a dependent oxygen process and is controlled by intrinsic factors (genetic and hormonal) as well as extrinsic factors (ultraviolet radiation). Melanogenesis is stimulated by stimulant melanocytic hormone, adrenocorticotropin hormone, estrogens and progesterone. The present review aimed to provide a summary of recent data about melanogenesis physiology.