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 regularly exposed to sunlight, the human skin is extremely well adapted to continuous UV stress. Well-pigmented skin is clearly better protected than white 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 common type of
cancer in the U.S.A. and Australia, which appears to be the result of an 'unnatural displacement' of people with sun-sensitive skin to sub-tropical regions. Although campaigns have been successful in informing people about the risks of sun exposure, general attitudes and behaviour do not yet appear to have changed to the extent that trends in
skin cancer morbidity and the corresponding burden on public healthcare will be reversed. The relationship between
skin cancer and regular sun exposure was suspected by physicians in the late 19th century, and subsequently substantiated in animal 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 1940 it was shown that the wavelength dependence of mutagenicity paralleled the UV absorption by
DNA. In the 1970s research on UV
carcinogenesis received a new impetus from the arising concern about a possible future depletion of the
stratospheric ozone layer: the resulting increases in ambient UV loads were expected to raise
skin cancer incidences. Epidemiological studies in the last decades of the 20th century have greatly refined our knowledge on the aetiology of
skin cancers. Analyses of gene mutations in skin
carcinomas have identified UV radiation as the cause. The relationship between the most fatal
skin cancer, i.e.
malignant melanoma and solar UV exposure is, however, still unclear and needs to be clarified to optimise preventive measures and minimise mortality from
skin cancers.