Secondhand smoke is a potent asthma trigger, especially for children. What happens if you reduce children’s exposure? A recent study in the Annals of Allergy, Asthma & Immunology offers proof of the benefits.

The study looked at trends in children’s emergency room visits for asthma in states that passed indoor smoking bans in places like restaurants, bars and workplaces. Even though children may spend less time in these places than adults, the results were stunning: a 17% decline in ER visits occurred over the first three years of the ban. The study involved 335,558 ER visits in 20 hospitals in 14 states.

The data “shows how important clean air is to children’s health,” says Tonya Winders, president and CEO of Allergy & Asthma Network. “If this much improvement can come from reducing secondhand smoke in public places, think how much of an impact parents can make by not smoking at home or in cars with children.”

Researchers point out the study doesn’t prove cause-and-effect, but does show a strong association. There was no general, nationwide decline in asthma-related ER visits beyond those seen in communities with smoking bans.