Asthma
Asthma, disorder of the respiratory system in which the passages that enable air to pass into and out of the lungs periodically narrow, causing coughing, wheezing, and shortness of breath. This narrowing is typically temporary and reversible, but in severe attacks, asthma may result in death. Asthma most commonly refers to bronchial asthma, an inflammation of the airways, but the term is also used to refer to cardiac asthma, which develops when fluid builds up in the lungs as a complication of heart failure. This article focuses on bronchial asthma. Asthma attacks are caused by airway hyperresponsiveness—that is, an overreaction of the bronchi and bronchioles to various environmental and physiological stimuli, known as triggers. The most common causes of asthma attacks are extremely small and lightweight particles transported through the air and inhaled into the lungs. When they enter the airways, these particles, known as environmental triggers, cause an inflammatory response in the