[The skin and the environment].

The skin is in such continuous and intimate interaction with environmental influences as no other organ. Environment comes in contact with the organism in the form of substances or forces (physical, chemical, biological) and via different routes: irradiation (electromagnetic irradiation, often referred to in a simplified way as "light"), air, food, direct contact with the skin, injection, or psychosocial interactions. All these influences can lead to disease under certain conditions and in certain individuals, and especially to skin disease. The critical factors are the dose, the mode and time of contact; this is evident with regard to sunlight and its acute and chronic effects. Not only for noxious chemicals are the classification and differentiation of primary toxic reactions from hypersensitivity reactions of predisposed individuals crucial. Hypersensitivity reactions can either be immunologically mediated (allergic) or non-immunological (idiosyncrasy, pseudo-allergy). The existence of a genetic disposition does not exclude the importance of environmental factors. Atopic eczema is an example of a disease that can be influenced dramatically by a variety of environmental factors. Many toxic environmental factors are known to induce skin changes long before systemic or life-threatening diseases appear. The skin can be regarded as a "signal organ" for possible noxious environmental influences. Increased research efforts in this field are mandatory.