Asthma and Air Pollution. Where Are We?

Asthma incidence and prevalence have increased in the last decades, suggesting a role of environmental factors including air pollution. In this manuscript, we summarize the evidence of the role of air pollution on (i) asthma exacerbations, (ii) asthma incidence in children, and (iii) asthma incidence in adults, pointing out the most important publications in each of these three areas. There is solid evidence that air pollution causes asthma exacerbations, characterized by hospital admissions, emergency department or doctor’s visits, medication intake, or absenteeism. The evidence regarding the effect of long-term air pollution exposure on asthma onset is also quite robust. In children, many studies have associated air pollution or proximity to traffic with asthma incidence, and while there are some negative publications, the evidence for an association is appealing. In adults, several studies also point to a positive association between air pollution and asthma incidence. Furthermore, there is a lot of knowledge about the mechanisms of the different agents involved. Gases, that are oxidants, could be more associated with acute manifestations of the disease and particles, more related with chronic inflammation, could be more associated with incidence. Diesel particles have been associated with both exacerbations and incidence. However, research is still needed to better understand and identify the underlying mechanisms related to the specific pollutants and specific sources. More research is also needed to identify more susceptible groups such as males, non-smokers, or persons with another chronic condition such as atopy or obesity.