Air pollution and allergy
Epidemiological studies especially in industrialized countries have found an increase in the prevalence of allergic diseases to be associated with pollution from vehicular exhaust. Invariably it has been noted that the prevalence of allergic diseases is higher in polluted areas than in unpolluted ones. Thus, those living in the cities are more vulnerable than those living in rural areas. In recent years, the number of cars with diesel engines has increased rapidly, and it has been calculated that 35-80% of suspended particulate matter in large cities consists of diesel exhaust particulates. Pyrene is the major compound of diesel exhaust particles and has been demonstrated to be the main culprit for promoting nasal allergy.

It has been found that suspended particulate matter has a direct promoting effect on the IgE antibody production. People breathing suspended particulate matter of diesel exhaust had enhanced total IgE and specific IgE production in fluids collected from the nose. Furthermore, it has been demonstrated that diesel exhaust particles had an enhancing effect on Th2-type (allergy-type) cytokine synthesis. Thus, people exposed to diesel fumes even for short periods have serious allergic reaction to aeroallergens, for example, dust mites allergens or pollens. Thus, vehicular exhausts are strong promoters of allergy and asthma.