Asthma is a chronic, long-term inflammation of the airways or bronchi of the lungs (the tubes that branch from the wind pipe) that results in intermittent and reversible narrowing of the airways. About 5% of adults and 10% of children in most Western populations have asthma.

Symptoms of asthma include breathlessness, wheeze (noisy breathing), and cough. A majority of asthmatics have allergic triggers such as animal danders or dust mites for their symptoms. Asthma attacks (worsening of symptoms) may be provoked by virus infections, allergen exposure, irritants such as smoke or some medicines.

Treatment with inhalers or other medication controls asthma for most asthmatics but does not cure the disease and many continue to have symptoms. About 2% of asthmatics are severely limited by their disease despite treatment and up to 1000 people a year die from asthma in the UK.