What is Hypersensitivity Pneumonitis?

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  • Written By: D. Jeffress
  • Edited By: Bronwyn Harris
  • Last Modified Date: 29 May 2019
  • Copyright Protected:
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Hypersensitivity pneumonitis refers to a group of syndromes that cause lung inflammation. A person can suffer from an acute or chronic inflammation after breathing in airborne dust that contains antigens, such as animal dander, mold spores, or toxic chemicals. Antigens attach to the small air sacs in the lungs, leading to severe irritation and inflammation of lung tissue. Most acute cases can be relieved by simply avoiding further exposure to the antigens, though chronic pneumonitis usually needs to be treated with prescription anti-inflammatory drugs.

Acute hypersensitivity pneumonitis typically occurs within six hours of heavy exposure to antigens. It is common in farm workers who are exposed to moldy hay and grains, raw dairy products, and farm animals. Bird owners and veterinarians might develop the condition after breathing in dander and airborne particles from animal waste. An old air conditioner or humidifier can also release hazardous mold into the air.

Most people who develop the acute form of pneumonitis experience severe chills, fever, headaches, and fatigue. Coughing and shortness of breath are common, along with a sore throat and chest pain. Symptoms typically persist for about 12 hours after exposure. Medical treatment is not normally needed to recover from acute hypersensitivity pneumonitis; simply avoiding the irritant prompts a quick recovery. People can usually prevent future episodes by wearing a respirator when working around foreign substances.


Chronic hypersensitivity pneumonitis is the result of long-term exposure to toxic chemicals and other airborne antigens. The condition is most prevalent in people who work in plastic and rubber manufacturing plants, lumber mills, and other industrial settings where chemicals or mold may be present. A person with chronic pneumonitis usually develops a persistent dry cough, weight loss, and shortness of breath. Medical evaluation is important to find relief from symptoms and prevent permanent lung damage.

A doctor can check for signs of chronic hypersensitivity pneumonitis by listening to the lungs with a stethoscope. Chest x-rays and computerized tomography scans can further reveal signs of inflammation. In addition, specialists may need to take blood samples or lung biopsies to confirm the diagnosis and ensure that the patient is not suffering from a more severe condition like lung cancer.

Since the lungs have already been damaged, limiting exposure to antigens does not usually relieve symptoms in patients with chronic hypersensitivity pneumonitis. Doctors typically prescribe corticosteroids to control the inflammatory response and promote lung tissue healing. Patients are encouraged to meet with their physicians regularly to monitor the healing process. It is possible to experience a full recovery from chronic pneumonitis, though it can take several years for the lungs to return to their normal level of functioning.



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