Asthma is caused by congestion of the bronchial tubes, which are the small air passages in the lungs. During an asthma attack, the air passages in the lungs narrow or become blocked by mucus or a muscle spasm. This makes breathing difficult and causes wheezing or coughing. An attack can be triggered by allergens such as pollen, animal dander, or house dust. It can also be caused by a respiratory infection or emotional stress.
Irritants including tobacco smoke, smog, and other chemicals are also factors.
A sudden change in temperature or humidity and strong winds can trigger an attack and so can strenuous exercise. The best way to control asthma is to avoid the things that cause it. Being healthy also helps prevent asthma attacks, so eat right, get enough sleep and exercise sensibly. It may be necessary for your doctor to prescribe medication to help prevent attacks or to stop them after they begin. Because asthma can be fatal if it isn't controlled, you should be under a doctor's care if you have the condition.