Photodermatoses in pigmented skin.

Photodermatoses are a group of skin diseases primarily caused by, or exacerbated by exposure to ultraviolet and or visible radiation. The effect of sunlight on skin depends on a number of factors including skin colour, skin phototype and the content and type of melanin in the skin. There are only a few studies describing photodermatoses in populations with dark skin. A PubMed search was conducted to summarize currently available information on differences in biology of melanin in dark and light skin and photodermatoses in dark skin. Dark skin is characterised by higher content of melanin, higher eumelanin to pheomelanin ratio, lower tyrosinase activity, and more effective distribution of melanin for protection against ultraviolet light. Photodermatoses are common in dark skinned patients with some variation in the spectrum of photodermatoses. Polymorphous light eruption (PMLE) is the commonest, followed by chronic actinic dermatitis. Pin-point papular and lichenoid variants of PMLE and actinic lichen planus are more frequent in dark skin whereas actinic prurigo, solar urticaria and hydroa vacciniforme are uncommon. Photodermatoses are common in dark skinned patients despite better natural photoprotection. It is proposed that lichenoid photodermatoses may be added to the classification of photodermatoses in dark skin.