HYGIENE HYPOTHESIS AND ALLERGIC DISEASES: REVISED

Abstract

Frequent upper respiratory infections and exposure to environmental endotoxin during early in life protect infants from subsequent allergic sensitization against airborne antigen and from development of asthma; this phenomenon was referred as to ''Hygiene Hypothesis''. These microbial stimuli shift airborne antigen-specific immune responses towards Th1 through activation of innate immune system. On the other hand, individuals with impaired immune responses against common cold viruses, including respiratory syncytial virus and rhinovirus, or those with impaired responses against bacterial pathogens locally have been shown to have strong risks of subsequent asthma or atopic dermatitis. These local immune responses play critical roles in the development of allergic diseases, and genetic backgrounds of such allergic phenotypes should be further investigated.