Hygiene Hypothesis: What Is the Current Thinking?

Abstract

Purpose of Review: Our aim was to discuss the hygiene hypothesis and current thinking about it. Recent Findings: Hygiene hypothesis suggests that an underlying reason for the recent prominent rise in allergic diseases may be linked with the diminution of the incidence of early childhood infections, which can be transmitted by means of contact with older siblings. Hygiene hypothesis suggests that contact with microbes in the environment in early life through pets, unpasteurized food, and nonsterilized water may protect from atopic diseases. Exposure to microbial pathogens and animals in infancy prevents atopy by Th1-like cytokine responses or by modifying Th2-like immune responses. Chronic infection and inflammation may protect against atopic disease. Alteration of exposure to microorganisms and access to clean water as well as issues related with food, sanitation, medical and obstetric practices, and urban lifestyle may have significant roles. Decreased exposure to bacteria in the early infancy period may shift the immune system to a predominantly Th2 state which is detected in atopic cases. Environmental exposure may lead to epigenetic changes which causes a shift of immune reactions against microorganisms. Summary: The hygiene hypothesis implies that modern living conditions can be responsible for the rise in the incidences of allergic disease and asthma. Protective effect of food-borne microbes on allergic diseases is another remarkable issue. © 2017, Springer Science+Business Media, LLC