Hygiene Can Hurt

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Science  08 Jun 2012:
Vol. 336, Issue 6086, pp. 1211-1213
DOI: 10.1126/science.336.6086.1211-d

As human societies urbanize, chronic inflammatory disorders become more apparent. The hygiene hypothesis suggests that individuals exposed to infection in childhood are less likely to develop inflammatory disease because exposure to microorganisms is important for stimulating responses that maintain epithelial cell integrity. Hence, in urban environments, reduced contact with the full diversity of the microbial world may be leading to the increased incidence of inflammatory disorders. Hanski et al. took a random sample of 118 adolescents from towns, villages, and isolated dwellings in eastern Finland, tested their immune function and allergic responses, surveyed their skin microflora, and investigated the biodiversity within their homes. They found several significant correlations, not least that low biodiversity was surprisingly strongly associated with atopy, and concluded that humans need to interact with natural environments for their physical health, not just for their peace of mind.

Proc. Natl. Acad. Sci. U.S.A. 109, 10.1073/pnas.1205624109 (2012).

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