Asthma is a common condition in which there is a narrowing of the small air passages (bronchial tubes) in the lungs.
The narrowing is caused by swelling in the lining of the bronchial tubes and tightening of the muscle in the wall of the bronchial tubes, and by and increased production of mucus. This reduces the flow of air in and out of the lungs and results in wheezing, cough and difficulties in breathing.
