Teenagers living close to a busy road are more likely to have allergies and asthma than those living farther from traffic, a study of one shantytown in Peru suggests.

The findings, published in the Journal of Allergy & Clinical Immunology, extend evidence linking traffic pollution to children’s asthma risk. Until now, most studies have been done in urban areas of wealthier nations, where specific pollution sources can be hard to pin down.

But in the shantytown in the current study - located in the outskirts of Lima - there is only one high-traffic roadway. And there are no nearby sources of industrial air pollution, said senior researcher Dr. William Checkley, of Johns Hopkins University in Baltimore, Maryland.

That setting, he told Reuters Health, makes it easier to zero in on the potential effects of road traffic on asthma risk.

Checkley and his colleagues studied 725 kids between the ages of 13 and 15 and found that roughly one in 10 had asthma symptoms in the previous year. And those who lived within 100 meters (328 feet) of the main roadway were twice as likely to have symptoms as those who lived at least 384 meters (1,260 feet) away.

The researchers also found that the teenagers’ risk of atopy - a tendency to have allergic reactions - inched up the closer they lived to the main road.

When the research team measured kids’ allergic tendencies using skin-prick tests, 56 percent of the teens overall had a skin reaction to at least one allergen - such as mold, dust mites or cat hair. Their odds of having a reaction rose higher as the distance from their house to the road got shorter.

That, Checkley said, suggests that increased allergy risk could explain the higher asthma rates among teens living closest to the busy roadway. Earlier research has suggested that traffic pollutants combined with airborne allergens can make the immune system more likely to overreact to those allergens, he said.

The findings do not prove that traffic pollution causes allergies and asthma in some kids.

However, Checkley said, he and his colleagues accounted for a number of factors that could otherwise muddy the link between traffic and asthma risk - like the teenagers’ weight and smoking habits.

Poverty is also linked to an increased risk of childhood asthma. But families in the Lima shantytown are generally poor, whether they live near the main road or not. “This is a relatively homogenous community,” Checkley said.

The findings, he added, argue for better traffic control in the area.