Hypersensitivity pneumonitis

Hypersensitivity pneumonitis is inflammation of the lungs due to breathing in a foreign substance, usually certain types of dust, fungus, or molds.

Causes of hypersensitivity pneumonitis

Hypersensitivity pneumonitis usually occurs in people who work in places where there are high levels of organic dusts, fungus, or molds. Long-term exposure can lead to lung inflammation and scarring.

Hypersensitivity pneumonitis may also be caused by fungi or bacteria in humidifiers, heating systems, and air conditioners found in homes and offices. Exposure to certain chemicals, such as isocyanates or acid anhydrides, can also lead to hypersensitivity pneumonitis.

Examples of hypersensitivity pneumonitis include:

Bird fancier's lung
This is the most common type of hypersensitivity pneumonitis. It is caused by repeated or intense exposure to proteins found in the feathers or droppings of many species of birds.
Farmer's lung
This type of hypersensitivity pneumonitis is caused by exposure to dust from moldy hay, straw, and grain.

The chronic form of this condition can be prevented by avoiding the material that causes the lung inflammation.

Hypersensitivity pneumonitis symptoms

Symptoms of acute hypersensitivity pneumonitis often occur 4 to 6 hours after you have left the area where the offending substance is found. This makes it difficult to find a connection between your activity and the disease. Symptoms might resolve before you go back to the area where you encountered the substance.

Symptoms may include:

  • Chills
  • Cough
  • Fever
  • Feeling ill (malaise)
  • Shortness of breath

Symptoms of chronic hypersensitivity pneumonitis may include:

  • Breathlessness, especially with activity
  • Cough, often dry
  • Loss of appetite
  • Unintentional weight loss

Call your health-care provider right away if you develop symptoms of hypersensitivity pneumonitis.

Tests and examinations for hypersensitivity pneumonitis

Your health-care provider will perform a physical examination and ask about your symptoms. He or she may hear abnormal lung sounds called crackles (rales) when listening to your chest with a stethoscope.

Lung changes due to chronic hypersensitivity pneumonitis may be seen on a chest X-ray and/or CT scan. Other tests may include:

  • Bronchoscopy with washings, biopsy, and bronchoalveolar lavage
  • Pulmonary function tests
  • Complete blood count (CBC)
  • Hypersensitivity pneumonitis antibody blood test
  • Surgical lung biopsy

Hypersensitivity pneumonitis treatment

First, the offending substance must be identified. Treatment involves avoiding this substance in the future. Some people may need to change jobs if they cannot avoid the substance at work.

If you have a chronic form of this disease, your doctor may recommend that you take anti-inflammatory medicines, which include steroids and other agents.

Outlook for people with hypersensitivity pneumonitis

Most symptoms go away when you avoid or limit your exposure to the material that caused the problem. If prevention is made in the acute stage, the outlook is good. When it reaches the chronic stage, the disease might continue to progress, even if the offending substance is avoided.

Possible complications from hypersensitivity pneumonitis

The chronic form of this disease may lead to pulmonary fibrosis. This is a scarring of the lung tissue that often is not reversible. Eventually, end-stage lung disease and respiratory failure can occur.

Last reviewed: 
January 2018
Alternative Names: 
Extrinsic allergic alveolitis
Farmer's lung
Mushroom picker's disease
Humidifier or air-conditioner lung
Bird breeder's lung
Bird fancier's lung

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