Asthma is a chronic (long-term) lung condition. Air passages narrow and become inflamed. This leads to breathing difficulties and wheezing.
Asthma ranges from mild to severe. Some people have only occasional, mild symptoms. Others have nearly constant symptoms with severe, life-threatening flare-ups.
During an asthma attack, the airways become inflamed. They narrow as the muscles surrounding them constrict. Mucus produced by the inflammation fills the narrowed passageways. As a result, the flow of air is partially or completely blocked.
Asthma affects the lung's larger and smaller airways.
What causes asthma-related inflammation is not clear. But several environmental "triggers" have been identified.
Many asthma triggers are allergens. Allergens cause the immune system to overreact in some people. Common allergens include:
Animal dander and saliva
Also high on the list of asthma triggers are:
Viral infections, such as colds and influenza
Breathing cold, dry air
Environmental pollutants, such as:
For some people with severe asthma, no specific triggers can be identified.
Asthma can develop early, often before age 5. But its symptoms can begin at any age. The condition has a genetic (inherited) component. It often affects people with a family history of allergies.