What Is Hypersensitivity Pneumonitis?

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Hypersensitivity pneumonitis is a general term referring to lung tissue inflammation. Hypersensitivity pneumonitis results when substances (allergens) like mold or other particles irritate the air sacs of the lungs. People who are sensitive to certain allergens can develop a reaction. Hypersensitivity pneumonitis, it may be acute (of short duration or sudden onset) or chronic (long-term). Hypersensitivity pneumonitis is treatable and manageable, but it is possible to experience permanent scarring and damage to the lungs if the condition is able to advance.

Hypersensitivity pneumonitis is one of the most common types of interstitial lung disease (ILD). ILD conditions are known for causing progressive scarring of lung tissue.

Lung function test
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Unlike pneumonia—which is an infection—hypersensitivity pneumonitis is a type of allergic reaction. Both hypersensitivity pneumonitis and pneumonia describe lung inflammation. However, if your healthcare provider says you have hypersensitivity pneumonitis, they are likely referring to an inflammatory lung condition other than pneumonia.

Pneumonitis Symptoms

The symptoms of hypersensitivity pneumonitis vary from person to person in intensity, frequency, and severity. Symptoms are also dependent on whether the disease is acute or chronic.

Acute Hypersensitivity Pneumonitis

In acute cases, symptoms are sudden and last 12 hours to several days. Symptoms of acute cases of pneumonitis may include:

While acute hypersensitivity pneumonitis is not as serious as chronic pneumonitis, left undiagnosed or untreated, it may eventually develop into chronic pneumonitis.

According to the American Lung Association, about 5% of people with acute pneumonitis will develop chronic pneumonitis.

Chronic Hypersensitivity Pneumonitis

Signs and symptoms of chronic hypersensitivity pneumonitis are similar to the acute type, but these are more intense and last for more than a few weeks. Additional signs and symptoms may include:

  • Loss of appetite
  • Unintentional weight loss
  • Lung fibrosis (damaged and scarred lungs)
  • Finger and toe clubbing (widening and rounding of the digits)
  • Rales: Abnormal rattling sounds heard when examining unhealthy lungs with a stethoscope
  • Flu-like illness (fever, chills, muscle or joint pain, etc.)

Although rare, chronic pneumonitis can lead to irreversible lung tissue scarring, a condition called pulmonary fibrosis. Pulmonary fibrosis is a profoundly serious condition resulting from too little oxygen reaching the body’s tissues.

Symptoms of pulmonary fibrosis may include:

  • Fast, shallow breathing
  • Shortness of breath
  • A dry, hacking cough
  • Unintentional weight loss
  • Chronic fatigue
  • Finger and toe clubbing
  • Fever and/or chills
  • Headaches
  • Joint and/or muscle pain

The course for pulmonary fibrosis and severity of symptoms will vary from person to person. Some people will be become sick quickly with severe symptoms while others will experience moderate symptoms that come on slowly over a period of months or years.

When to See a Healthcare Provider

You should see your healthcare provider when symptoms are severe and not manageable. For example, if you experience severe, ongoing flu-like symptoms or signs of fluid in the lungs, these warrant an immediate visit to your healthcare provider.

Most people who get the flu will recover in a few days to two weeks. However, if symptoms last more than two weeks or if you start to experience breathing problems, high fever, or chest pain, you should call your healthcare provider right away.

Because hypersensitivity pneumonitis can lead to permanent lung damage, it is especially important to see a healthcare provider right away before symptoms are severe and impossible to treat with self-care.

Anytime hypersensitivity pneumonitis is left untreated, it can become life-threatening. This is because lung inflammation and other symptoms make it harder for the heart to pump blood through the lungs.


Fluid buildup in the lungs—whether related to hypersensitivity pneumonitis or another condition—can be life-threatening if not caught early on and treated. Your healthcare provider will look for this complication if you are diagnosed with chronic pneumonitis. You should share with your healthcare provider if you think you hear grunting, gurgling, or wheezing sounds with breathing.

More, severe symptoms of hypersensitivity pneumonitis can cause respiratory problems. Often this is the result of lung scarring, which may stop the lungs from working as effectively as they should. Additionally, the amount of oxygen reaching the bloodstream may be impaired.


Hhypersensitivity pneumonitis is the result of inhaling allergens and certain substances. Hundreds of substances are known for causing pneumonitis, including:

  • Molds, fungi, and other pathogens
  • Chemicals
  • Proteins
  • Bacteria and mycobacteria

These substances are known for causing lung tissue inflammation when inhaled. If there is repeated exposure to the allergen, the lungs will remain inflamed. A person is more likely to develop chronic hypersensitivity pneumonitis if they are continually exposed to low levels of allergens over a period of months or years.

Risk Factors

Certain risk factors can increase your risk of developing hypersensitivity pneumonitis. These include age, gender, environment, job, family history, lifestyle, and having other medical conditions.

Age: Hypersensitivity pneumonitis can affect anyone of any age, but it is most often diagnosed in people ages 50 to 55. It is also a common type of childhood chronic interstitial lung disease.

Gender: Some studies have found hypersensitivity pneumonitis is more common in women, but the differences between men and women are relatively small.

Environmental: Environmental exposure alone is not enough to cause chronic hypersensitivity pneumonitis, but can cause immune system reactions, especially combined with other risk factors.

Job: Repeated exposure to certain chemicals on the job can cause hypersensitivity pneumonitis and certain occupations can increase risk. These include farming and other occupations that involve caring for animals or birds, woodworking, and winemaking. A person can be exposed to similar substances in their own homes that may increase risk, including from their pets, especially birds.

Family history and genetics: Genetics are thought to predispose some people to pneumonitis. But because only a small part of the population develops the condition, genetic predisposition to pneumonitis is yet to be proved. However, in some families, more than one person can develop the condition. When more than one person in the family has hypersensitivity pneumonitis, the condition is familial hypersensitivity pneumonitis. Researchers are starting to look at genetic immune system proteins that may increase risk, as they believe these may explain why people with the same genetic makeup may have the same response to certain substance exposures.

Lifestyle: While smoking may not increase the risk of developing hypersensitivity pneumonitis, it can worsen the condition and cause serious complications. If you have been diagnosed with hypersensitivity pneumonitis, talk to your healthcare provider about how you can quit smoking to reduce your risk for serious complications of the disease.

Medical conditions: Some viral infections may increase a person’s for developing hypersensitivity pneumonitis.

You should see your healthcare provider if you have symptoms of hypersensitivity pneumonitis, especially breathing problems. The sooner you seek medical attention, the more likely you can reduce your risk for complications and the effects of this condition.


Symptoms of hypersensitivity pneumonitis are similar to those of other lung conditions. That means your healthcare provider will need to perform several tests before making a diagnosis. Your healthcare provider will also want to rule out other possible conditions.

Your healthcare provider will suspect hypersensitivity pneumonitis if you share you have come in contact with any of the substances that cause hypersensitivity pneumonitis. Determining this starts with a medical history and a physical exam.

Your healthcare provider may request additional testing, including

  • Bloodwork can evaluate white blood cell levels in your body (to look for signs of infection) and other markers that a person is currently experiencing an immune system reaction. Blood testing for antibodies to mold, dust, and other allergens may be performed.
  • Imaging including computed tomography (CT) scans and X-rays to look for inflammation or fluid in the lungs
  • Spirometry to see how your lungs are faring when you breathe in and out
  • Oximetry to check the amount of oxygen in the bloodstream
  • A lung biopsy to check lung tissue for signs of pneumonitis
  • A bronchoscopy to examine the lungs and collect tissue and fluid samples. A bronchoscopy involves inserting a thin, flexible tube (bronchoscope) down the throat into the airways . The bronchoscope has a light and camera attached to it, allowing the clinician to see inside the airways


Once you have been diagnosed with hypersensitivity pneumonitis, if you can identify the source of the reaction, your healthcare provider will recommend you avoid it. Talk to your healthcare provider about the ways in which you can avoid or eliminate the allergen from your home or workplace. If hypersensitivity pneumonitis is diagnosed early enough, the damage can be reversed, and lungs can return to normal.

In severe cases, avoiding the source of symptoms may not be enough. You healthcare provider may prescribe other treatments, including:

  • Corticosteroids: These medications are available as a pill or injection and are used to help reduce inflammation.
  • Oxygen therapy: Your healthcare provider will prescribe supplemental oxygen if you are having breathing problems.
  • Bronchodilators: These medications relax the airways so you can breathe better.
  • Lung transplant: If your lung is severely damaged, you may need a lung transplant. You will have to wait on a waiting list for a matched donor.

A Word From Verywell

The best way to prevent hypersensitivity pneumonitis is to be aware of what substances may cause you to develop the condition and to avoid those. Routine checking of heating, cooling, and ventilation units can reduce airborne irritants in your home and potentially reduce the risk for hypersensitivity pneumonitis. You should also be aware of any allergies you may have, and possible allergens in your home or workplace. If you need to be in areas where you may be exposed to allergens, wearing a face mask that covers the mouth and nose can reduce exposure.

Hypersensitivity pneumonitis leads to severe complications if left untreated. You should, therefore, be aware of the symptoms and get treated as soon as possible if you experience them, especially shortness of breath and other breathing problems.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  3. American Lung Association. Learn about hypersensitivity pneumonitis.

  4. National Heart, Lung, and Blood Institute. Hypersensitivity pneumonitis.

  5. Cleveland Clinic. Idiopathic pulmonary fibrosis.

  6. Centers for Disease Control and Prevention. Flu symptoms & complications.

  7. Penn Medicine. Pulmonary edema.

  8. Falfán-Valencia R, Camarena A, Pineda CL, et al. Genetic susceptibility to multicase hypersensitivity pneumonitis is associated with the TNF-238 GG genotype of the promoter region and HLA-DRB1*04 bearing HLA haplotypes. Respir Med. 2014;108(1):211‐217. doi:10.1016/j.rmed.2013.11.004

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  10. National Heart, Lung, and Blood Institute. Bronchoscopy.

By Lana Barhum
Lana Barhum has been a freelance medical writer since 2009. She shares advice on living well with chronic disease.