Who's at risk?

> Asthma affects people of all ages, but it most often starts during childhood. In the United States, more than 22 million people are known to have asthma. Nearly 6 million of these people are children.

> Young children who often wheeze and have respiratory infections—as well as certain other risk factors—are at highest risk of developing asthma that continues beyond 6 years of age. The other risk factors include having allergies, eczema (an allergic skin condition), or parents who have asthma.

> Among children, more boys have asthma than girls. But among adults, more women have the disease than men. It's not clear whether or how sex and sex hormones play a role in causing asthma.

> Most, but not all, people who have asthma have allergies.