title: The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human skin.
abstract: The relationship between human skin pigmentation and protection from ultraviolet (UV) radiation is an important element underlying differences in skin carcinogenesis rates. The association between UV damage and the risk of skin cancer is clear, yet a strategic balance in exposure to UV needs to be met. Dark skin is protected from UV-induced DNA damage significantly more than light skin owing to the constitutively higher pigmentation, but an as yet unresolved and important question is what photoprotective benefit, if any, is afforded by facultative pigmentation (i.e. a tan induced by UV exposure). To address that and to compare the effects of various wavelengths of UV, we repetitively exposed human skin to suberythemal doses of UVA and/or UVB over 2 weeks after which a challenge dose of UVA and UVB was given. Although visual skin pigmentation (tanning) elicited by different UV exposure protocols was similar, the melanin content and UV-protective effects against DNA damage in UVB-tanned skin (but not in UVA-tanned skin) were significantly higher. UVA-induced tans seem to result from the photooxidation of existing melanin and its precursors with some redistribution of pigment granules, while UVB stimulates melanocytes to up-regulate melanin synthesis and increases pigmentation coverage, effects that are synergistically stimulated in UVA and UVB-exposed skin. Thus, UVA tanning contributes essentially no photoprotection, although all types of UV-induced tanning result in DNA and cellular damage, which can eventually lead to photocarcinogenesis.
authors.affiliation: Laboratory of Cell Biology, National Cancer Institute, Bethesda, MD, USA.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Miyamura
authors.forename: Sergio G
authors.initials: SG
authors.lastname: Coelho
authors.forename: Kathrin
authors.initials: K
authors.lastname: Schlenz
authors.forename: Jan
authors.initials: J
authors.lastname: Batzer
authors.forename: Christoph
authors.initials: C
authors.lastname: Smuda
authors.forename: Wonseon
authors.initials: W
authors.lastname: Choi
authors.forename: Michaela
authors.initials: M
authors.lastname: Brenner
authors.forename: Thierry
authors.initials: T
authors.lastname: Passeron
authors.forename: Guofeng
authors.initials: G
authors.lastname: Zhang
authors.forename: Ludger
authors.initials: L
authors.lastname: Kolbe
authors.forename: Rainer
authors.initials: R
authors.lastname: Wolber
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Hearing
mesh_terms: D004249:DNA Damage; D006801:Humans; D008543:Melanins / Q000378:metabolism; D020011:Protective Agents; D011740:Pyrimidine Dimers / Q000378:metabolism; D012867:Skin / Q000378:metabolism / Q000528:radiation effects*; D012880:Skin Pigmentation / Q000528:radiation effects; D017768:Skin, Artificial; D055108:Sunbathing; D014466:Ultraviolet Rays
chemical_list: D008543:Melanins; D020011:Protective Agents; D011740:Pyrimidine Dimers