Causes of Asthma

Asthma is a chronic inflammatory disorder of the airways caused by an immune system abnormality that appears to have both genetic and environmental components. The two defining features of asthma are inflammation and oversensitivity (hyper-reactivity) of the airways, both of which lead to obstruction of airflow.

Airway inflammation involves swelling of the lining of the airway and excessive production and accumulation of mucus. These problems can be aggravated by a respiratory infection such as sinusitis, flu, or a cold. Hyper-reactive airways tend to "twitch" when exposed to allergens and other irritants, causing the muscles around the airways to contract. Both inflammation and hyper-reactivity cause narrowing of the airways, making it difficult to breathe.

Although asthma is characterized by repeated attacks (during which symptoms progressively worsen), airway inflammation may persist even when symptoms are absent and may therefore require long-term treatment with medication.

The irritants that can cause the airways to twitch, narrow and become plugged with sticky mucus vary with age. In people who develop asthma before age 30, attacks are more likely to be triggered by exposure to a specific environmental irritant, such as cigarette smoke, industrial fumes, pollen, mold, dust, animal dander or saliva, and perfumes. Exercise, cold or dry air, emotional stress, and gastroesophageal reflux disease (GERD) are more likely to trigger attacks in people who develop asthma after age 30.

Asthma Symptoms

The onset of an asthma attack may be gradual or sudden. Some attacks get better on their own, but most require medication. Milder attacks are most common and usually begin with tightness in the chest and a cough.

Breathing may be accompanied by wheezing as well as by restlessness and difficulty sleeping. Sometimes mild attacks seem to improve for a while, only to be followed by the reappearance of persistent symptoms that require treatment in a hospital.

During a severe asthma attack, extreme shortness of breath is accompanied by

  • wheezing
  • tightness in the chest
  • coughing up thick phlegm
  • sweating
  • faster breathing
  • rapid pulse

Symptoms of asthma may last for only a few minutes, particularly if they are treated promptly, or they may last for hours or days, even with medication. Coughing can continue for a week or longer after other acute symptoms disappear.

Publication Review By: Peter B. Terry, M.D., M.A.

Published: 02 Aug 2011

Last Modified: 17 Oct 2014