This article is a commentary on the following study: Penard-Morand C, Charpin D, Raherison C, Kopferschmitt C, Caillaud D, Lavaud F, Annesi-Maesano I. Long-term exposure to background air pollution and its association with respiratory and allergic health in schoolchildren. Clin Exp Allergy. 2005 Oct;30(10):1279-87. Numerous epidemiological studies have demonstrated the impact of background pollution from NO2, SO2, PM, and O3 on chronic respiratory symptoms and lung function. However, no association has been demonstrated between background pollution, asthma, and allergic sensitization, except for ozone, where two studies show correlations with asthma and bronchial hyperreactivity. Epidemiological studies have focused on the effects of motor vehicle traffic and have shown positive associations between respiratory disorders, lung function, and allergic rhinitis, whereas the results were rather contradictory for asthma and atopic dermatitis. The study aims to contribute to the debate regarding the impact of background pollution on asthma and allergies. The authors present an epidemiological study designed to investigate an association between long-term exposure to background pollution on the one hand, and atopic dermatitis and respiratory disorders on the other, in a population of school-aged children. This study confirms the findings reported by other authors, particularly the lack of health effects from NO₂ at the levels observed in this study. It also highlights the limitations of the indicators typically used to characterize air quality in certain epidemiological studies. (Excerpts from the article)