Asthma is a disease of the respiratory system. Its chief feature is difficult breathing, often accompanied by a wheezing or whistling sound during exhalation.
Asthma attacks occur at varying intervals, and the seriousness of the attacks can vary.
Between attacks, asthmatics are usually completely free of respiratory symptoms. During an asthmatic attack, the muscles of the smaller bronchi and lungs go into a spasm. The airways narrow and it is more difficult for air to get in and out of the lungs. The lining of the airways becomes congested and swollen and secretes excess mucus, which adds to the breathing problem. An asthma attack may be caused by many different things including allergies, respiratory infections, and behavioral and environmental factors.