Advertising campaigns such as ‘Slip Slop Slap’ (slip on a shirt, slop on some sunscreen and slap on a hat) have made most people aware of the risks of skin cancer with exposure to the ultraviolet rays of the sun. Greater exposure to ultraviolet radiation could be expected with depletion of the protective ozone layer in the upper atmosphere. Non-melanoma skin cancers are the commonest cancers in the world and are increasing.
Melanoma skin cancers are particularly nasty — if they spread beyond the skin they have a high death rate. Prolonged exposure to the sun, such as may occur with outdoor occupations or sun-worshipping, is associated with the development of non-melanoma skin cancers. Ultraviolet rays damage DNA which eventually leads to the formation of a cancer. Melanomas result from intense exposure to the sun with episodes of acute sunburn. Exposure to ultraviolet rays not only damages DNA but also suppresses the immune system, which makes it easier for skin cancers to develop.
Skin cancer is far more common in white populations, particularly if they have migrated to latitudes with greater sun exposure. The melanin pigment in the skin protects darker-skinned people. Australian Aborigines, for example, develop melanomas only on depigmented areas such as the soles and palms or the lining of the mouth. There is a genetic predisposition to melanoma which makes it more likely in some individuals.
Another condition predisposing to skin cancer is the genetically inherited disease, xeroderma pigmentosum. This reduces the ability of cells to repair ultraviolet damage to DNA, thus increasing the risk of sun-related skin cancers.