A growing number of people in some developed countries including the USA develop a long-term illness called asthma, which predominantly affects the airways of the lungs and triggers difficulty breathing.

It's apparent that certain pollutants in the air are able to initiate an asthma attack. However, the exact contribution of long-term exposure to pollutants to the pathogenesis of childhood asthma has not been completely understood.

Described in the Journal of Allergy and Clinical Immunology, a new study (Lifetime air pollution exposure and asthma in a pediatric birth cohort) has unraveled that long-term exposure to pollutants from traffic greatly increases children's likelihood of developing asthma.

The new study is a collaboration of Beth Israel Deaconess Medical Center, Harvard Medical School and Harvard Pilgrim Health Care Institute, Brigham and Women's Hospital, National Institutes of Health, University of the Negev, and Harvard T.H. Chan School of Public Health, and is built on previous work showing that living near to a roadway, where there are much more traffic pollutants in the air, is connected to reduced lung function in kids aged 7 to 10.

The aim of the new study is to determine whether exposure to traffic pollutants is also linked to asthma. In the study, data from a large number of kids and their mothers were analyzed, including information about sleep and eating habits, exposure to pollutants such as fine particulate matter (PM), histories of residential address, and so on.

Fine PM refers to tiny particles or droplets that float in the air for a prolonged period of time, which may include aerosols, smoke, fumes, dust, ash, and pollen. These small particles are emitted from a wide range of sources, especially fuel combustion including traffic and power plants, and construction sites.

Notably, the researchers found a strong connection between living close to a major road and childhood asthma. Comparing the chance of kids who lived less than 100m away from a major road with that of those who lived more than 400m away from a major road, the researchers noticed that kids living near to a major road were much more likely to have current asthma.

Furthermore, there was a gender difference. For kids aged 3 to 5, fine PM and black carbon correlated with asthma, while for kids aged 7-10, such association was found in girls but not in boys. This might be because of younger kids' longer time at home and smaller airways.

To conclude, the study reveals a close association between long-term pollution exposure and asthma in young kids.

In addition to environmental factors, asthma also involves genetic factors. So far, many genes including GSTM1, IL10, CTLA-4, SPINK5, LTC4S, IL4R and ADAM33 have been demonstrated to affect the risk of asthma.

Understanding how these factors affect the pathogenesis of childhood asthma will lead to more effective strategies to prevent the illness and allow our kids to enjoy their childhood to the full.