The 'hygiene hypothesis' was popularized in the late 1980s to explain the high prevalence of atopic disorders in the developed countries. It links atopic disorders and the lack of early life infections. An association between the two is not novel and dates back to the beginnings of allergy, immunology and microbiology. Allergy and infection have always been closely related and the study of one has often provided new insights into the pathobiology of the other. Early research into bacterial infections led to the discovery of the human immune system and the concept of allergy. An important relationship exists between parasite infections and the development of atopic disorders. This review traces the long and intimate historical relationship between infection and allergy.