Stephen J.LurieMD, PhD, Senior EditorIndividualAuthorPhil B.FontanarosaMD, Executive Deputy EditorIndividualAuthor
To the Editor: While the prevalence of asthma
and allergic disease is increasing worldwide,1
both diseases appear to be less common in rural settings in developing countries
and farming communities in industrialized countries.2
Indeed, some locales seem to be almost free of asthma.3
To explain the low prevalence of asthma in these settings, the "hygiene hypothesis"
suggests that early childhood exposure to high levels of bacterial and viral
pathogens leads to a lower risk of asthma and atopy.4,5
The immune response to these infections would presumably inhibit helper T
cell type 2 (TH2)–type allergic responses.
Gereda JE, Leung DYM, Liu AH. Levels of Environmental Endotoxin and Prevalence of Atopic Disease. JAMA. 2000;284(13):1652-1653. doi:10.1001/jama.284.13.1647