Asthma is a lung condition that causes difficulty breathing.
Asthma affects the bronchial tubes, also known as airways. When a person breathes normally, air is taken in through the nose or mouth and then goes into the trachea (windpipe), passing through the bronchial tubes, into the lungs, and finally back out again.
But people with asthma have airways that are inflamed. This means that they swell and produce lots of thick mucus. The airways are also overly sensitive, or hyperreactive, to certain things, like exercise, dust, or cigarette smoke. This hyperreactivity causes the smooth muscle that surrounds the airways to tighten up.
The combination of airway inflammation and muscle tightening narrows the airways and makes it difficult for air to move through. When a person has a lot of trouble with wheezing, coughing, or shortness of breath, it's called an asthma flare-up, or asthma attack.
No one knows exactly what causes asthma. It's thought to be a combination of environmental and genetic (hereditary) factors. There's no cure for asthma, but it usually can be managed and flare-ups can be prevented. Although medications can play an essential role in preventing flare-ups, environmental control (avoiding contact with the allergens or irritants that cause the flare-ups) is also very important.
All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.
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