With every breath, the human lung is exposed to a myriad of particles. While some of the inhaled particles are harmless, a large proportion of these particles (the exact amount depends on the current environment) has allergen potential. In susceptible individuals, allergens induce sensitization and a chronic inflammatory response in target organs (airways, skin), which typically includes the production of antigen-specific immunoglobulin E (IgE). Allergens recognized by human IgE sera of more than 50% of patients in a clinically sensitive group are called major allergens. In contrast, allergens not important for the major population, but on individual basis, are called minor allergens. Over the past 25 years, an increase in the prevalence of aeroallergen sensitization has occurred in all age groups, affecting over 25% of the population (1).