A person with asthma has an illness that causes swelling and narrowing of tiny air passages, called bronchioles. During an asthma attack, air has difficulty passing through the narrowed bronchioles. As air passes through the narrowed bronchioles, it makes a whistling noise, called wheezing.

Asthma is more common in children than in adults. Asthma is often triggered by allergies, changes in weather, exercise, and stress. Asthma that is triggered by exposure to something in the workplace is called occupational asthma.

Most people with asthma respond well to treatment with medications.