Skin cancer and solar UV radiation

Ultraviolet (UV) radiation in sunlight is the most prominent and ubiquitous physical carcinogen in our natural environment. It is highly genotoxic but does not penetrate the body any deeper than the skin. Like all organisms r egularly exposed to sunlight, the human skin is extremely well adapted to c ontinuous UV stress. Web-pigmented skin is clearly better protected than wh ite Caucasian skin. The sun-seeking habits of white Caucasians in developed countries are likely to have contributed strongly to the increase in skin cancer observed over the last century. Skin cancer is by far the most commo n type of cancer in the U.S.A. and Australia, which appears to be the resul t of an 'unnatural displacement' of people with sun-sensitive skin to sub-t ropical regions. Although campaigns have been successful in informing peopl e about the risks of sun exposure, general attitudes and behaviour do not y et appear to have changed to the extent that trends in skin cancer morbidit y and the corresponding burden on public healthcare will be reversed. The r elationship between skin cancer and regular sun exposure was suspected by p hysicians in the late 19th century, and subsequently substantiated in anima l experiments in the early part of the 20th century. UV radiation was found to be highly genotoxic, and DNA repair proved to be crucial in fending off detrimental effects such as mutagenesis and cell death. In fact, around 19 40 it was shown that the wavelength dependence of mutagenicity paralleled t he UV absorption by DNA. In the 1970s research on UV carcinogenesis receive d a new impetus from the arising concern about a possible future depletion of the stratospheric ozone layer: the resulting increases in ambient UV loa ds were expected to raise skin cancer incidences. Epidemiological studies i n the last decades of the 20th century have greatly refined our knowledge o n the aetiology of skin cancers. Analyses of gene mutations in skin carcino mas leave identified UV radiation as the cause. The relationship between th e most fatal skin cancer, i.e. malignant melanoma and solar UV exposure is, however, still unclear and needs to be clarified to optimise preventive me asures and minimise mortality from skin cancers. (C) 1999 Elsevier Science Ltd. All rights reserved.