The human skin is one of the major human organs in perpetual interaction with environmental factors. Permanent micro-aggressions by light, mecanical factors or chemical factors are useful for the maintenance of healthy skin. For example light is necessary for vitamin D synthesis and for the control of skin inflammation If the aggression is too strong, repair mecanisms are involved such as wound healing or DNA repair. Accumulation of aggressions could induce acute or chronic diseases such as sunburn, photoageing or skin carcinoma. On specific individuals with genetic predisposition environmental aggressions can induce frequent, diseases such as atopic dermatitis, present in 20 % of children or psoriasis, present in 2-3 % of the European population. Chemical aggressions are responsible for irritant dermatitis or allergic dermatitis, which are among the most frequent professional diseases. Agression by UV light is one of the best examples of the interaction between environment and health. At a low dose UV light is very good for the health. At a high dose it is responsible for photoageing and skin carcinoma. To improve the control of environmental factors important fur health, two approaches are essential: 1) research into epidemiology to discover thc causal relationships and into biology to discover the mecanisms involved; 2) education from childhood to explain the results of research and to propose effective behaviours. For each aggression individuals at risk have to be identified. (C) 2000 Academie dcs sciences/Editions scientifiques et medicales Elsevier SAS.
