Commentary: The end of the hygiene hypothesis?

This paper reviews a number of important pieces of evidence namely the high asthma prevalence in Latin America (which appears unlikely to have lower infection rates than Europe) and the decline in asthmas prevalence in both adults and children in Western countries (which are unlikely to have become “less clean” in recent decades). The basic message is that the hygiene hypothesis, particularly in its original form, does not explain by itself the changes in the prevalence of asthma (mostly) and atopic disease more generally. For asthma, one confounding factor is the proportion of non-allergic asthma (which accounts for more than 50%), which clearly would not be influenced by microbial exposure. For atopic disease more generally, the conclusion is that the hygiene hypothesis in its later manifestations can provide some mechanistic explanation for changing trends in prevalence, but that atopic disease is a multifactorial disease with many different elements modulating its development. Int J Epidemiol. 2008 Jun;37(3):570-2. Epub 2008 May 2.