Particulate and gaseous air pollutants are capable of damaging the airway epithelial lining and of shifting the local immune balance, thereby facilitating the induction of persistent inflammation. Epidemiological studies are inconclusive regarding whether air pollution increases the incidence of asthma and chronic bronchitis in the population. Clearly, environmental pollution can, however, precipitate attacks and emergency-room admissions in those already suffering from such conditions. The catastrophic potential of airborne pollution was demonstrated in the 1960s and 1970s, when inverted atmospheric pressure conditions trapped smog over cities on the Eastern coast of the United States and over Europe. This smog resulted in thousands of hospital admissions and dozens of deaths. With the general rise in the incidence of atopy and asthma in the Western population, it is of major public health interest to reduce, as much as possible, the exposure of such populations to anthropogenic and natural sources of pollution.