Asthma is not a disease itself, but a symptom of some other condition. When a person has asthma, he finds it hard to breathe because there is an obstruction to the flow of air into and out of the lungs.

This barrier or obstruction may be caused by a swelling of the mucous membranes, or by a constriction of the tubes leading from the windpipe to the lungs. When a person has an attack of asthma, he develops shortness or breath, wheezing, and coughing. The attack may come on gradually or develop suddenly.