Definition of Pneumonitis

Inflammation of the lungs resulting from exposure to an irritant. The inflammation causes the airways to narrow and to increase mucus secretion, reducing the pathways for the flow of air. The major types are

  • aspiration pneumonitis, which develops when foreign matter, such as vomitus or water, enters the airways and lungs
  • chemical pneumonitis, which results from inhaling toxic fumes
  • hypersensitivity pneumonitis, which is an immune reaction to an inhaled substance
  • radiation pneumonitis, which occurs as a side effect of radiation therapy to the chest and lower neck, such as to treat lung cancer, thyroid cancer, or breast cancer


The primary symptoms of pneumonitis are persistent cough and dyspnea (shortness of breath). The doctor makes the diagnosis on the basis of the history of the symptoms, including when they began, what circumstances existed, and in particular any known or suspected exposures that occurred. Near drowning, for example, may result in aspiration of water. Swallowing disorders may allow food or drink to enter the airways.

Chemical pneumonitis and hypersensitivity pneumonitis often result from occupational exposures (and sometimes exposure to pets such as birds) and may indicate the early stages of pulmonary disease related to exposures such as to dusts and fibers. Chest X-ray, arterial blood gases, pulmonary function tests, and chest computed tomography (chest CT) are among the diagnostic procedures that may help identify the extent of pulmonary involvement and its effect on oxygenation.


Treatment is often corticosteroid medications to relieve inflammation, which may allow the lungs to return to normal function. The doctor may also prescribe antibiotic medications to treat secondary infection if present, or when the cause of the pneumonitis is bacterial infection. Elimination of irritants, when known, prevents the pneumonitis from recurring. Most people recover fully and without complications after the inflammation subsides. Chronic pneumonitis may result in scarring (fibrosis) and permanent damage to pulmonary structures, however.


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