Kids who live near air pollution caused by traffic may suffer from more severe asthma, according to new findings.

A study published in the journal Annals of Allergy, Asthma and Immunology found children who are exposed to more traffic-related air pollutants tend to make more hospital visits related to their condition.

Dr. Ralph J. Delfino and colleagues at the University of California-Irvine looked at medical records related to more than 2,700 children, analyzing their estimated exposure to nitrogen oxides and carbon monoxides.

After adjusting for factors including poverty, race/ethnicity and health insurance, they found an association between traffic-related pollutants and trips to health facilities.

The majority of these hospital encounters were noted in children between the ages of 1 and 3, which the report said may indicate early exposure may provide the most significant link.

According to the researchers, the findings suggest that “local traffic-generated air pollution near the home affects asthma symptom severity.”

Approximately nine million children under 18 have been diagnosed with asthma, figures from the American Academy of Allergy Asthma & Immunology reveal.