ABSTRACT
Melanocytes are pigment-producing cells that are located in the basal layer of the epidermis and hair follicles. Melaninogenesis is a complex process with different stages that leads to the production and transportation of melanin. The process of melaninogenesis is completed in three stages. The first stage is the addition of cysteine to dopaquinone and the production of cysteinyldopas. The second stage is the production of pheomelanin by the oxidation of cysteinyldopas, and the third stage is the production of eumelanin. The eumelanin/pheomelanin ratio is affected by cysteine concentration and tyrosinase activity. Pigmentation defects, classified as hypo- or hyperpigmentation, could be caused by an alteration during the process of melaninogenesis. There are several pathways, proteins, and mechanisms that regulate melaninogenesis and several melanogenic inhibitors. The most important pathways are the cyclic adenosine monophosphate (cAMP)-dependent and the protein kinase C (PKC)-dependent pathways. Ultraviolet radiation (UVR) is considered the most important extraneous regulator of melaninogenesis.
