Hygiene hypothesis questioned

A new study by a team at Stanford questions the controversial hygiene hypothesis, which states that raising children in an overly clean environment leads to the development of asthma. But others in the field say the paper, in the February 16 Nature Immunology, does little to challenge the theory.

Martin Dahl and colleagues at Stanford University School of Medicine report that infection with influenza A increases the likelihood of developing allergic disease, potentially undermining a key tenet of the hypothesis: namely, that being infected with viruses protects against other diseases (Nature Immunology, DOI:10.1038/ni1041, February 16, 2004).

“There has been this very popular idea of the mutually exclusive response for some infections,” David B. Lewis, associate professor of pediatrics at Stanford University School of Medicine and coauthor of the paper, said, referring to T-helper 1 (TH1) and TH2 responses. The TH1 response produces high levels of interferon γ that can decrease ...