A dramatic increase in the prevalence of allergic respiratory diseases such as rhinosinusitis and bronchial asthma has been observed during the last 3 decades in industrialized  countries [1-6].

The key feature of bronchial asthma is the development of airway infl ammation and bronchial hyperresponsiveness in the form of a heightened bronchoconstrictor response, not only to allergens to which an individual is sensitized, but also to a range of nonspecifi c stimuli, such as air pollutants and cold air [7-14]. There is some evidence to indicate that high levels of vehicle emissions in cities and an urban lifestyle are correlated with the rising trend in allergic respiratory diseases [7-12]. The adverse effect of air pollution on respiratory health has a quantifi able impact, not only on the morbidity but also on the mortality of respiratory diseases  [15-17]. One commonly proposed explanation for the recent increase in morbidity associated with allergic respiratory diseases is the continuous degradation of air quality as a result of increasing levels of outdoor air pollutants such as vehicle emissions [7-20].

An understanding of the interplay between genetic background and environmental pollution may lead to interventions that can prevent the progression of asthma, the onset of airway infl ammation with bronchial hyperresponsiveness to various specifi c and nonspecifi c stimuli, and the development of irreversible changes in airway function. It is not easy to evaluate the impact of air pollution on the timing of asthma exacerbations or on the prevalence of asthma in general, since atmospheric concentrations of airborne allergens and air pollutants frequently increase simultaneously. However, some trials have evaluated the role of exposure to air pollution in reducing the threshold concentration of aeroallergens able to induce airway responsiveness to a specifi c bronchial challenge in sensitized subjects [7,9,10]. Factors such as type of air pollution, climate, plant species, degree of airway sensitization, and hyperresponsiveness of exposed individuals can infl uence this interaction. Positive associations have been observed between urban air pollution and respiratory symptoms in children, and the literature contains many reports of a relation between motor vehicle exhausts and acute or chronic respiratory symptoms in children living near traffic [17-58]. Air pollution can negatively influence lung development in children and  adolescents