Asthma is a predisposition to chronic inflammation of the lungs in which the airways (bronchi) are reversibly narrowed. Asthma affects 7% of the population, and 300 million worldwide. During asthma attacks (exacerbations of asthma), the smooth muscle cells in the bronchi constrict, and the airways become inflamed and swollen. Breathing becomes difficult. Attacks can be prevented by avoiding triggering factors and by drug treatment. Drugs are used for acute attacks, commonly inhaled beta-2 agonists.
