Environmental factors in nonmelanoma and melanoma skin cancer.

We discuss the role of sunlight, mostly ultraviolet light (UV), in the induction of nonmelanoma and melanoma skin cancer. Whilst the former seems to be correlated with accumulated exposure, the causation of melanoma is more complex, and may also involve the pattern of, and age at, exposure. The efficacy of sunscreens is debatable; while they protect against UVB wavelengths (290-320 nm), and so extend the time that may be spent in the sun before becoming sunburnt, their use may subject wearers to excessive exposure to UVA (320-400 nm) and visible light. Both epidemiological surveys and experiments with animal models suggest that UVA, and perhaps the visible, may induce melanomas. Although Japanese have a much lower incidence of skin cancer than Caucasians, the dramatic rise in skin cancer in Japanese-Americans in Hawaii exposed to high-intensity irradiation raises concerns. If the Japanese people adopt sun-seeking behavior, or should the levels of UV irradiation rise significantly through depletion of the ozone layer, then this could become an important health problem in future.