The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human skin.
Pigment Cell Melanoma Res. 2011 Feb ;24(1):136-47. Epub 2010 Oct 6. PMID: 20979596
Yoshinori Miyamura, Sergio G Coelho, Kathrin Schlenz, Jan Batzer, Christoph Smuda, Wonseon Choi, Michaela Brenner, Thierry Passeron, Guofeng Zhang, Ludger Kolbe, Rainer Wolber, Vincent J Hearing
Laboratory of Cell Biology, National Cancer
Institute, Bethesda, MD, USA.
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.
Article Published Date : Feb 01, 2011