Expert consensus document: The international scientific association for probiotics and prebiotics consensus statement on the scope and appropriate use of the term probiotic
Allergies represent a condition where impaired immunological tolerance to common environmental allergens is the fundamental determinant of the disease. The immunopathological 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.