[Does reduced microbial exposure contribute to increased prevalence of allergy?]

Diseases associated with atopic allergy such as asthma, hay fever and eczema have increased dramatically in westernised societies over the last decades. Reduced microbial exposure during the first years of life, which we find in societies with a high standard of living, may be disadvantageous in terms of mucosal sensitisation to allergy. Recent studies have suggested an inverse relationship between allergic disorders and infections with intracellular pathogens including tuberculosis, measles, and hepatitis A. Because many intracellular pathogens generate predominantly a T helper 1 (Th1)-cell cytokine profile, and because Th1 and Th2 cell-mediated immune mechanisms are subjected to cross-regulation, it is possible that exposure to certain microorganisms may repress or abolish development of atopic allergy.