Asthma is a chronic inflammation of the lungs in which the airways (bronchi) are reversibly narrowed. Asthma affects 7% of the population, and 300 million worldwide. During attacks (exacerbations), the smooth muscle cells in the bronchi constrict, and the airways become inflamed and swollen. Breathing becomes difficult, and asthma causes 4,000 deaths a year in the U.S. Attacks can be prevented by avoiding triggering factors and by drug treatment. Drugs are used for acute attacks, commonly inhaled β2-agonists. In more serious cases, drugs are used for long-term prevention, starting with inhaled corticosteroids, and then long-acting β2-agonists if necessary. Leukotriene antagonists are less effective than corticosteroids but have no side effects. Monoclonal antibodies such as mepolizumab and omalizumab are sometimes effective. Prognosis is good with treatment.

In contrast to chronic obstructive pulmonary disease and chronic bronchitis, the inflammation of asthma is reversible. In contrast to emphysema, asthma affects the bronchi, not the alveoli.

The National Heart, Lung and Blood Institute defines asthma as a common chronic disorder of the airways characterized by variable and recurring symptoms, airflow obstruction, bronchial hyperresponsiveness (bronchospasm), and an underlying inflammation.

Public attention in the developed world has recently focused on asthma because of its rapidly increasing prevalence, affecting up to one in four urban children.

For more information about Asthma, read the full article at Wikipedia.
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