Ageing of the skin results from the synergistic effects of intrinsic, genetically determined factors and extrinsic factors the most important of which is chronic exposure to sunlight. The cumulative effects of ultraviolet radiations are responsible for specific dermo-epidermal alterations (actinodermatitis) with its two main manifestations: actinic elastosis characterized by accumulation of dystrophic fibres in the dermis, and lesions of senile keratosis which may become carcinomas. The so-called "premature ageing of the skin" can be alleviated by cosmetic treatments, photoprotective measures and vitamin A derivatives; regular applications of retinoic acid (vitamin A acid, tretinoin) can result in partial regression of actinodermatitis.