Hypersensitivity pneumonitis (HP) is an inflammation of the lung, usually of the very small airways. It is caused by the body’s immune reaction to small air-borne particles. These particles can be bacteria, mold, fungi, or even inorganic matter.

Hypersensitivity pneumonitis can either be acute or chronic.

  • Acute Hypersensitivity Pneumonitis tends to occur 4-12 hours after exposure (usually heavy exposure) to the particles.
  • Chronic Hypersensitivity Pneumonitis is a long-term condition that causes lung scarring (fibrosis).

Symptoms of acute hypersensitivity pneumonitis include:

  • Fever
  • Chills
  • Coughing
  • Shortness of Breath
  • Body Aches, Malaise

Symptoms of chronic hypersensitivity pneumonitis include:

  • Shortness of breath
  • Cough


Many people with episodes of hypersensitivity pneumonitis are probably unrecognized and undiagnosed. Some cases believed to be viral pneumonias may actually be hypersensitivity pneumonitis. The patient’s history of repeated episodes of typical symptoms, hours after exposure to certain environments are important in establishing the diagnosis.

Diagnosis may include:

  • Chest X-ray may show a variety of abnormalities, but primarily increased lung markings.
  • High resolution cat scan of the chest is often reviewed. This study shows a detailed image of the appearance of the lung tissue.
  • Lung function tests that examine the lung volumes and the ability for gases to move through the lungs (diffusing capacity) are then performed.
  • CT scan and pulmonary function tests are also useful in diagnosis and in following response to therapy.
  • Blood antibody tests and skin tests against certain offending molds, bacteria, or particles are available, but their results are usually inconclusive.
  • Serum KL-6 (Krebs von den Lungen-6) this test may act as a marker for activity seen in diffuse lung disease.
  • Video Assisted Thoracoscopic Surgery (VATS), which is an open lung biopsy technique performed by thoracic surgeons under general anesthesia. This procedure allows for a larger sample size and more accurate diagnosis.

The interpretation of these tests is complicated, and is best performed by a doctor experienced in hypersensitivity pneumonitis, often with the help of a pathologist experienced in lung diseases.



The most important treatment of hypersensitivity pneumonitis is avoidance of repeated exposures to the offending particles. With early diagnosis and prevention, the prognosis is good. Prolonged, repeated exposures can lead to permanent lung damage, scarring, and potentially significant disability.

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