The role of the microbial environment for the development of childhood asthma and allergies

Asthma and allergies are among the most frequent chronic diseases in childhood. Their prevalence has increased during the second half of the twentieth century but seem to stabilize in recent years in many Western European countries such as Switzerland. Although the genetic background is known to have a strong impact on an individual ' s risk to develop asthma or allergy it seems likely that environmental factors are mostly responsible for the increase in prevalence over time. Much research has been devoted to environmental risk factors promoting the development of asthma and allergies. Yet, there is increasing interest in environmental factors which might protect from the development of these diseases and which might have been reduced along with the development of a "Western lifestyle". The role of environmental allergens, the hygiene hypothesis and the role of the farm environment on the development of asthma and allergies are discussed. An emphasis is put on the microbial environment as encountered in the farming environment which has been shown to confer protection from the development of asthma and allergies. It is likely that among other factors the development of a "Western lifestyle" went along with a marked change of the microbial environment children are exposed to.