Abstract
The atopic diseases - atopic dermatitis, asthma, and hay fever - pose a great burden to the individual and society, not least, since these diseases have reached epidemic proportions during the past decades in industrialized and, more recently, in developing countries. Whereas the prevalence of the atopic diseases now seems to have reached a plateau in many Western countries, they are still on the increase in the developing world. This emphasizes continuing research aimed at identifying the causes, risk factors, and natural history of these diseases. Herein, the fundamental aspects of the natural history and epidemiology of the atopic diseases are reviewed.