The pathogenesis of allergic diseases involves complex interactions between well- characterized environmental allergens and poorly-understood genetic factors. In addition, the decline in the number of infectious stimuli during the development of the immune system may contribute to allergy pathogenesis, a paradigm called "Hygiene Hypothesis" that supports the steep rise of allergies in developed populations. In contrast to the effect of environmental allergens, pathogenic and non-pathogenic microoganisms or their structural components can exert pressure on the immune system to modulate the development of allergic responses. Furthermore, the effect of different polymorphisms may play important role in an individual's predisposition to allergic diseases. In recent years, findings on the combined effect of environmental allergens, genetic polymorphisms, the absence of infections and other environmental factors are starting to converge, producing fascinating results on gene-environment interactions that may explain the development of allergies.
Understanding the biochemical nature of allergens and the identification of genetic polymorphisms implicated in allergies has advanced our knowledge on the disease prevalence, healthcare burden and pathogenesis of allergies. Elucidating the mechanisms of interactions between the genes and the allergens involved in the pathogenesis of allergic diseases will help enhance the present medical armamentarium for the diagnosis and therapy of allergies.