Cumulative effects of ultraviolet radiation on the skin: cancer and photoaging.

The cumulative effects of solar exposure are skin cancer and photoaging. This relationship has been established by epidemiological, clinical, and pathological investigation. Understanding of the mechanisms of skin cancer and photoaging requires the study of model systems. For example, the study of cancerprone xeroderma pigmentosum patients has indicated that effective DNA repair is a major defence mechanism against skin cancer. However, there are few human models. The hairless albino mouse has been shown to be a good model for both photocarcinogenesis by ultraviolet radiation (UVR) alone and UVR in association with 8-methoxypsoralen and photoaging and may provide much information on mechanistic aspects. The use of sunscreens is often advocated as a means of preventing the cumulative effects of solar exposure. Animal data support this approach but such data must be interpreted with caution.