ABSTRACT
Allergies represent a condition where impaired immunological tolerance to common
environmental allergens is the fundamental determinant of the disease. The immuno-
pathological mechanism of the disease development is poorly understood. It is thought to
involve complex genetic predisposition, which depending on environmental triggers
and/or protective factors, may lead to allergic sensitization and development of allergic
disease and the consequent symptoms (1-5). One environmental factor that has received
particular interest in recent years is the variation in early microbial exposure, which has
indisputable, although incompletely understood, effects on immunological maturation.
Wider acknowledgment of the possible association between microbes and allergic
diseases followed the introduction of what became known as “hygiene hypothesis” by
Strachan, 1989 (6). Based upon epidemiological findings, he suggested that the rise in
prevalence of allergic diseases in past decades was due to factors associated with changes
in life style such as reduced family size and improved hygiene measures. He assumed that
these epidemiological correlations reflected reduced opportunities for cross-infections in
families with young children.
