Among the theories supporting the increase of incidence of allergy during the last several decades is the concept that environmental pollutants may play a vital role. The present review reported the effect of different types of pollutants on the development, modulation and persistence of allergic reactions. It analyzed how pollutants including ozone, nitrogen dioxide and particulate materials contribute to allergy directly and indirectly. It reviewed several possible mechanisms involved in the enhancement of allergic inflammation by air pollutants. Finally, it made a delineation of many factors affecting allergy, which could provide useful information on the prevention of allergy.