What is Asthma?
According to the American Lung Association, 20 million Americans have asthma, a disease which causes swelling and the build up of mucus in the tubes that block air from going in and out of the lungs.
Breathing is sometimes difficult for people with asthma because there is less room for air to travel to and from the lungs. Usually the airways in their lungs narrow temporarily or fill with mucus because they are exposed to something. It could be something the person is allergic to (an allergen) like dust or pollen, or something that irritates the lungs, like smoke or smog.