Air Pollution and Allergies: A Connection?

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Medical Author: Alan Szeftel, MD, FCCP
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

Does the "air we breathe" have an impact on the rising incidence of allergies and asthma? Hay fever was rare in Japan before World War II. However, pollen allergy is now common and mostly affects those living in Japanese cities and near highways. Allergic disease is also more common in highly developed countries in North America and Europe and less common in Third World countries. This suggests that there must be something about modern, urban life that promotes allergy. Let us examine the impact of air pollution.

By far the most important indoor pollutant is tobacco smoke, which is strongly associated with allergic sensitization, asthma, and other respiratory illnesses. Exposure to smoke results in the body's enhanced ability to produce IgE (the allergy antibody) that attaches to allergens (e.g. pollen, dust mites and dander). The IgE response is a key trigger of allergic reactions. Parental smoking increases the risk of their children having many respiratory illnesses, including bronchitis, chronic cough, and asthma. Smoking during pregnancy and breastfeeding results in a higher risk for the children to develop allergic eczema (atopic dermatitis). The rate of asthma in an infant of a smoking mother is double that of a non-smoking mother. This is very important, since in North America, 25% of mothers smoke during pregnancy and 40% have a smoker in the home.

The increased rates of allergy and asthma in city environments and in those living close to highways has drawn attention to the role of outdoor pollution. Common air pollutants, such as ozone, sulfur dioxide, and nitrogen dioxide probably act more as irritants than as promoters of sensitization. These pollutants have been shown to be hazardous to adults and children with asthma. Recent studies suggest that prematurely born children are more sensitive to the respiratory effects of outdoor pollution. There may also be an association with diesel exhaust particles and the worldwide increase in respiratory allergies. Diesel exhaust has been shown to enhance the ability to make the allergy antibody, IgE, in response to exposure to allergens.

What is the bottom line? Tobacco smoke is by far the worst and most important air pollutant and it clearly promotes both allergy and asthma. Diesel fumes likely promote allergy, whereas other outdoor air pollutants act more as irritants that can aggravate allergies and asthma, rather than as true promoters of allergy or asthma.