History
Although the idea that exposure to certain infections may decrease the risk of an allergy is not new, David P. Strachan was the first scientist who gave the theory a scientific background in an article published in the British Medical Journal (now the BMJ), in 1989. In this article, the hygiene hypothesis was proposed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were presumably exposed to more infectious agents through their siblings, than in children from families with only one child.
The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that has been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents.
Read more about this topic: Hygiene Hypothesis
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—Charlie Dunbar Broad (1887–1971)
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—Henry David Thoreau (1817–1862)