The Hygiene Hypothesis: How Early-Life Microbial Exposure May Influence Allergic Diseases

Over the past half century, allergic diseases such as asthma, atopic eczema, hay fever and food allergy have risen dramatically, particularly in industrialized, urbanized societies. In 1989, epidemiologist David Strachan proposed what became known as the 'hygiene hypothesis': a lack of early-childhood exposure to infectious agents, and more broadly to a diverse microbial environment, may disturb the development of the immune system and predispose a child to allergic disease. Since then, the hypothesis has evolved considerably.