Asthma, which typically begins in childhood and is the most common chronic disease of childhood, has reached epidemic proportions. Asthma is associated with gene-environment interactions, and there is consensus that a "window of opportunity" exists early in life when environmental factors may influence its development. This review considers biologic and sociologic factors in the development of allergy and asthma. Meta-analysis of studies demonstrates that monoallergen reduction does not impact asthma prevention. However, multifaceted allergen reduction studies have shown clinical benefit. We propose that allergic diseases, including asthma, represent a dysfunctional interaction with our environment and that the increasing prevalence of asthma and allergy herald increased population risk for the development of other inflammatory and autoimmune diseases. Better understanding of the complex factors for asthma and allergies may provide insight into many other chronic complex diseases.