Photo‐Induced Events in the Human Melanocytic System: Photoaggression and Photoprotection

Abstract

The human skin is submitted to solar, essentially ultraviolet radiation (UVR), aggressions, and develops, for sufficient doses, erythema and pigmentation. The individual sun-sensitivity depends on the nature and the quantity of melanins present in the epidermis. These parameters are inherited as genetic traits which account for the large variations of the constitutive and adaptive pigmentation encountered in the caucasian populations. From red-haired skin-sensitive individuals, to dark-haired sun-resistant individuals, phaeomelanins (red) and eumelanins (black) are mixed in variable proportions. Pure melanins extracted from red hairs and black hairs behave differently when submitted to ultraviolet radiations: phaeomelanins develop aggressive species of molecules responsible for DNA damages, mutations, and cell death. On the contrary, eumelanins are less toxic for the major cellular metabolisms. The sun-sensitive populations suffer from more skin cancer of all types than the dark ones. In particular, they are exposed significantly to higher risk of melanoma and to the risk of bearing more nevi following large solar exposures early in the life.

Dietary Monounsaturated Fatty Acids Intake and Risk of Skin Photoaging

“…For geographical location, France was arbitrarily divided into North and South areas using the northern frontier of Aquitaine, Limousin, Auvergne, and Rhône-Alpes regions. In addition, skin phototype was determined at baseline according to the classification proposed by Césarini: I, II, IIIa, IIIb, IV, V, VI [27]. Levels I and VI, which were rare in our population, have been grouped with levels II and V respectively.…”

Icnirp Statement—protection of Workers Against Ultraviolet Radiation

“…The wide range of susceptibility to solar exposure among phototypes (Table 1) largely corresponds with two types of melanin produced by melanocytes: eumelanin (dark brown-black) and phaeomelanin (yellow-red) (Hönigsmann et al 1986;Césarini 1988;Young 1994Young , 2004. Phaeomelanin absorbs UVR photons and with overexposure produces reactive oxygen species (ROS) which are phototoxic (Fitzpatrick and Szabo 1983).…”

Cutaneous Photobiology. The Melanocyte vs. the Sun: Who Will Win the Final Round?

“…Studies on purified eumelanin and pheomelanin showed that irradiation of pheomelanin results in the generation of hydroxyl radicals and superoxide anions that might contribute to oxidative DNA damage. Additionally, pheomelanin increases the release of histamine, which contributes to the sun‐induced erythema and edema in fair skinned individuals (49). Exposure of the skin to UV reduces the levels of glutathione reductase, which is important for pheomelanin synthesis, and is more prevalent in light‐colored than in dark skin (50–52).…”