Asthma is a chronic disorder characterized by shortness of breath, wheezing, coughing and tightness of the chest.

This happens in the respiratory system where the airways constrict, become inflamed, and are lined with excessive amounts of mucus, usually in response to one or more "triggers," such as exposure to an allergen, cold air, exercise, or stress.

In children, the most common triggers are viral illnesses such as those that cause the common cold. This airway narrowing causes symptoms such as wheezing, shortness of breath, chest tightness, and coughing, which respond to bronchodilators. Between episodes, most people feel fine.