Photoprotection versus photodamage: updating an old but still unsolved controversy about melanin

Melanin is the main pigment in animal skin. It is a heterogeneous polyphenolic molecule with a generalized absorption in the UV-visible range synthesized in melanocytes, a kind of specialized epidermal cells. There are two types of melanin, eumelanin and pheomelanin, more abundant in dark or fair skin respectively. Melanin plays several roles, but in mammalian skin the main one is related to photoprotection against sunlight. The absorption energy from UV light implies that elements of the melanin structure are photoexcited, and the subsequent transference of energy can provoke several effects on surrounding molecules. These processes raise the possibility that melanin becomes a photosensitizer instead of a photoprotector. Thus, melanins should be considered double-faced molecules. This was first evident for pheomelanin, but very recent new data on eumelanin indicate that the balance is subtler than thought so far, and photodamage can overcome photoprotection for both types. In this updated review, the consequences of the eumelanin versus pheomelanin photochemical properties are discussed in relation to DNA lesions. Melanin is considered photoprotective, but it can also produce DNA photodamage and this would be related to the high incidence of skin cancer, mostly in Caucasian people. (c) 2016 Society of Chemical Industry