In recent years, the rapid increase in the number of patients with environmental hypersensitivity has become a worldwide problem, and although it has been pointed out that the condition is closely related to allergic diseases, its pathogenesis remains to be elucidated. Environmental hypersensitivity is a health disorder characterized by a variety of systemic symptoms, including autonomic and endocrine symptoms, immune and allergic symptoms, chronic pain and fatigue, memory and emotional disorders, and hypersensitivity to external environmental stimuli in daily life. Typical examples include sick building syndrome, multiple chemical sensitivity, and electromagnetic hypersensitivity. Over the past 30 years, I have conducted multifaceted epidemiological investigations, including the development of a Japanese translation of the international common questionnaire to evaluate environmental hypersensitivity, the confirmation of its reliability and validity, and the setting of screening thresholds unique to Japan. In this paper, I describe the latest findings on environmental hypersensitivity and introduce some of the epidemiological studies conducted by the authors in Japan using the international common questionnaire.