A chronic, hypersensitive condition characterised by breathing difficulties caused by a narrowing of the air passage leading to the lungs.

The main symptoms are breathlessness and a wheezing cough that may worsen at night or early in the morning. In severe attacks, the breathing rate increases considerably and is rapid and shallow. It is caused by swelling and inflammation of the walls of the air passage, and contraction of the muscles, whereby openings are narrowed. Usually it is triggered by a number of different allergens.