Asthma is a common disease that occurs in the airways of the lungs known as the bronchial tubes. Normally when a person breathes in and out, the muscles surrounding these airways are relaxed, allowing air to move freely. But when a person has asthma, allergens, environmental triggers, or infections cause these muscles to tighten up, making it more difficult for air to move freely in and out of the airways and causing shortness of breath and a whistling or wheezing sound. This tightening, which is linked to persistent inflammation in the airways, is called “bronchospasm.” In some cases the airways can become swollen or filled with mucus as well, making breathing even more difficult.

About 12 to 15 million Americans are affected by asthma. Many people first have signs of the disease in childhood, but it’s important to note asthma can occur for the first time at any age. Particularly vulnerable are those with a family history of asthma or those with a history of allergies or exposure to tobacco smoke. Some people also have a form of the disease known as exercise-induced asthma, which is triggered by strenuous physical activity.

Created: September 2003
Reviewed: May 26, 2005
Revised: