The hygiene hypothesis

Abstract

Over the past decades, an increase of the prevalence of allergic diseases has been observed in Western countries. The hygiene hypothesis proposes that viral, bacterial, or helminth infections; environments with high levels of microbial components, such as farms; and the nutrition are preventive against the development of allergies despite the same genetic predisposition. The timing of these exposures is crucial. The critical window of time starts already in utero and ends in school age depending on the kind of exposure. The underlying immunological mechanism of such exposures seems rather to include the induction of regulatory processes to control the allergic reaction than to prevent the production of IgE. In this chapter, we review the best understood exposures together with the timing and the immunological mechanisms they induce to get the most preventive effect on the development of allergic diseases.