Many diseases are caused by exposure to environmental hazards. Although a high index of suspicion is essential for diagnosis, once diagnosed, environmentally-induced problems often respond to simple environmental solutions. Moreover, many patients are worried about elements of their environment that have little or no effect on health, so physicians need to be able to distinguish those which are hazardous from those which are not. Environmental factors are involved in the aetiology of virtually every illness. To diagnose illness predominantly environmental in origin, physicians have to include a thorough environmental assessment in their history-taking. Clues that an illness is caused by an environmental factor include: