Skip to main contentSkip to accessibility services
6 min read
No Ads

Hypersensitivity Pneumonitis: Symptoms, Causes, & Long-Term Treatment

Tooltip Icon.
Last updated September 21, 2020

Try our free symptom checker

Get a thorough self-assessment before your visit to the doctor.

Hypersensitivity pneumonitis occurs when something inhaled inflames the lungs such as exposure to mold, animals, grain/flour, or synthetic materials.

What is hypersensitivity pneumonitis?

Hypersensitivity pneumonitis occurs when something inhaled inflames the lungs. A variety of allergens can cause this immunologic reaction, both natural and synthetic. There are three forms of hypersensitivity pneumonitis acute, subacute, and chronic that are defined by how severe the symptoms are and how quickly they develop.

Symptoms include shortness of breath, cough, fever and chills, fatigue and weight loss, and thickening or increased curvature of the fingernails.

Treatments include reducing exposure to the inflammatory allergen, prescription of steroids or immunosuppressants, and, in severe cases, a lung transplant may be an option.

You should seek care promptly, preferably at your primary care physician, to get tested and treated.

Hypersensitivity pneumonitis symptoms

There are slight variations in both the time of onset and the severity of symptoms experienced in the three forms of hypersensitivity pneumonitis.

  • Acute: This form of hypersensitivity pneumonitis develops in four to six hours after heavy exposure to an allergen.
  • Subacute: This form of hypersensitivity pneumonitis develops more gradually or after repeated attacks of acute hypersensitivity pneumonitis.
  • Chronic: This form of hypersensitivity pneumonitis develops even more slowly but can be associated with the most severe symptoms.

All forms of hypersensitivity pneumonitis can be associated with the following symptoms.

  • Shortness of breath: All forms of hypersensitivity pneumonitis usually cause shortness of breath. The shortness of breath comes on suddenly in acute hypersensitivity pneumonitis and comes on more gradually in subacute and chronic hypersensitivity pneumonitis. This occurs because inflammation caused by the allergen damages the lungs.
  • Cough: All forms of hypersensitivity pneumonitis are also associated with the development of a cough, which can develop suddenly or gradually and may produce sputum.
  • Fever and chills: Acute hypersensitivity pneumonitis may cause a fever and chills that occur shortly after exposure to the allergen. The fever will usually go away once the allergen is removed.
  • Fatigue and weight loss: Subacute and chronic hypersensitivity pneumonitis may be associated with fatigue and weight loss over a longer period of time. This occurs because long-term exposure to the allergen causes continuous inflammation in the body.
  • Thickening and increased curvature of the fingernails: Chronic hypersensitivity pneumonitis that is not treated for a long time may cause thickening and increased curvature of the fingernails. These changes are known as "clubbing," and are a sign of more severe disease.

Hypersensitivity pneumonitis causes

Allergens that can cause the immunologic reaction experienced in hypersensitivity pneumonitis include microorganisms, insects, animals or animal products, or synthetic materials. Specific causes of hypersensitivity pneumonitis can be animal-related exposures or other environmental exposures, although there is usually some overlap for those who work in the farming industry.

Farming or cattle working

Exposure to farming or cattle causes the form of hypersensitivity pneumonitis also known as "farmer's lung," and is one of the most common types. Allergic agents that can cause farmer's lung include:

  • Moldy hay or crops
  • Tobacco plants
  • Mushroom spores
  • Moldy wine or cheese
  • Tea plants

Birds and poultry

Exposure to birds and poultry causes the form of hypersensitivity pneumonitis also known as "bird fancier's lung." Certain materials in bird droppings or feathers cause the allergic reaction that leads to hypersensitivity pneumonitis. This can also result from exposure to items that contain bird products, such as feather pillows and down comforters.

Other animals

Hypersensitivity pneumonitis can be seen in veterinarians or other occupations that require handling animals. Specific triggers that can cause the allergic reaction include:

  • Urine or fur of laboratory animals
  • Bat droppings
  • Fish meal
  • Oyster shells

Contaminated ventilation or water systems

Hypersensitivity pneumonitis occurs if ventilation or water systems are contaminated by microorganisms. These systems can include:

  • Air conditioners or humidifiers
  • Cool-mist vaporizers
  • Swimming pools
  • Hot tubs or spas
  • Water slides
  • Shower curtains

Lumber milling or construction

Exposure to wood through lumber milling or construction can also cause hypersensitivity pneumonitis. This can occur when the wood is colonized with mold, which can be inhaled and cause an allergic reaction.

Grain or flour processing

People who work in grain or flour processing or loading can develop hypersensitivity pneumonitis. Grain can become colonized by certain molds or insects, and because grain and flour can be easily aerosolized, the allergens can be inhaled and cause an allergic reaction.

Synthetic materials

The gases and aerosolized products in some synthetic materials can cause an allergic reaction in the lung. These include:

  • Plastic materials
  • Paints
  • Other chemicals

Treatment options and prevention

Hypersensitivity pneumonitis is a long-term condition that will require ongoing treatment to manage the symptoms. Living with the condition will likely require significant support. Managing hypersensitivity pneumonitis requires a combination of medications and behavioral changes. Specific treatments for hypersensitivity pneumonitis are usually recommended in the following order: reducing exposure to the allergen, steroids or immunosuppressants, and finally, a lung transplant.

Reducing exposure to the allergen

The first step to treating hypersensitivity pneumonitis is to identify then reduce exposure to the allergen that is causing inflammation. This may involve:

  • Animals: Getting rid of birds or other animals
  • Dust or debris: Regularly clean ventilation systems or other parts of the environment
  • Household items: Getting rid of items in the home such as feather pillows or down comforters
  • Relocation: Changing jobs or moving to a new home


Recommendation of either of these types of medication will depend on your specific case and medical history as both have different effects on the body.

  • Glucocorticoids: Some people with hypersensitivity pneumonitis may benefit from treatment with glucocorticoid (steroid) medications, which reduce inflammation, and may lead to a faster recovery. Glucocorticoid medications are particularly helpful for people with farmer's lung or bird fancier's lung. Specific glucocorticoid medications include prednisone or prednisolone.
  • Immunosuppressants: Some people with hypersensitivity pneumonitis may benefit from other medications that weaken the immune system and thus reduce inflammation. These medications include rituximab (Rituxan), azathioprine (Imuran), and mycophenolate (CellCept). However, these medications come with their own set of risks.

Lung transplant

For people with advanced hypersensitivity pneumonitis who don't benefit from other treatments, lung transplant may be an option.

  • Details: A lung transplant will replace the existing damaged lung with a healthy lung from a donor.
  • Prognosis: The new lung may subsequently develop hypersensitivity pneumonitis if you are still exposed to the same allergen.

When to seek further consultation

You should seek medical attention if you suffer any symptoms similar to hypersensitivity pneumonitis, or if you have trouble breathing. You should also consult your physician regularly if you are exposed to associated allergens for long periods of time.

If you develop any symptoms of hypersensitivity pneumonitis

If you are experiencing shortness of breath, cough, fever or chills, fatigue, or weight loss, you should see your physician. He or she can order tests and imaging to see if you have hypersensitivity pneumonitis and offer you the proper treatment. Your physician might also be able to help you identify the allergen that is causing the hypersensitivity pneumonitis, so you know what to avoid.

If you have ongoing exposure to a potential cause of hypersensitivity pneumonitis

If you suspect that repeated exposure to something in your home or workplace is causing symptoms of hypersensitivity pneumonitis, you can consider going to your physician. He or she can order tests or imaging to look for evidence to see if you may be having ongoing inflammation due to hypersensitivity pneumonitis symptoms.

Questions your doctor may ask to diagnose

  • Have you been feeling more tired than usual, lethargic or fatigued despite sleeping a normal amount?
  • Do you have a cough?
  • Are you sick enough to consider going to the emergency room right now?
  • Any fever today or during the last week?
  • Have you lost your appetite recently?

Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.

Share your story

Dr. Liu received his medical degree from the University of Pennsylvania Perelman School of Medicine and is pursuing a career in ophthalmology. He graduated Phi Beta Kappa from Swarthmore College with a BA in biology. He has published research in multiple ophthalmology and healthcare journals and has received awards from Research to Prevent Blindness. In his free time, he enjoys running, biking, and spending time with his friends and family.

Was this article helpful?

Tooltip Icon.
Read this next


  1. Hypersensitivity Pneumonitis. American Lung Association. American Lung Association
  2. Hypersensitivity Pneumonitis. National Institute of Health: National Heart, Lung, and Blood Institute. NHLBI Link
  3. Sforza GGR, Marinou A. Hypersensitivity Pneumonitis: A Complex Lung Disease. Clinical and Molecular Allergy. 2017;15:6. NCBI Link
  4. Adler LC. Clubbing of the Fingers or Toes. U.S. National Library of Medicine: MedlinePlus. Published August 31, 2018. MedlinePlus Link
  5. Cano-Jimnez E, Acua A, Botana MI, et al. Farmer's Lung Disease. A Review. Archivos de Bronconeumologa. 2016;52(6):321-328. NCBI Link
  6. Chan AL, Juarez MM, Leslie KO, et al. Bird Fancier's Lung: A State-of-the-Art Review. Clinical Reviews in Allergy & Immunology. 2012;43(1-2):69-83. NCBI Link
  7. Lung Helpline & Tobacco Quitline. American Lung Association. American Lung Association Link
  8. Quirce S, Sastre J. Hypersensitivity Pneumonitis in the Workplace. World Allergy Organization. Published September 2013. WAO Link
  9. Venkateshiah S. Hypersensitivity Pneumonitis. Chest Foundation. Published January 2018. Chest Foundation Link
  10. Adegunsoye A, Oldham JM, Fernndez Prez ER, et al. Outcomes of Immunosuppressive Therapy in Chronic Hypersensitivity Pneumonitis. ERJ Open Research. 2017;3(3):16-2017. NCBI Link
  11. Kern RM, Singer JP, Koth L, et al. Lung Transplantation for Hypersensitivity Pneumonitis. CHEST Journal. 2015;147(6):1558-1565. CHEST Link