What is asthma?
Asthma is a disease of the lungs. The airways of people who have asthma are extra sensitive to the things they're allergic to (called allergens) and to other irritating things in the air (called irritants).
Asthma symptoms start when allergens or other irritants cause the lining of the airways to become inflamed (swollen) and narrow. The muscles around the airways can then spasm (contract rapidly), causing the airways to narrow even more. When the lining of the airways is inflamed, it produces more mucus. The mucus clogs the airways and further blocks the flow of air. This is called an "asthma attack."
Some information adapted from "What you and your family can do about asthma," a patient information booklet published by the Global Initiative for Asthma, a joint effort of the National Heart, Lung, and Blood Institute and the World Health Organization. This and other publications are available through the Internet (http://www.ginasthma.com).
Written by familydoctor.org editorial staff