Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is a type of allergic reaction that causes inflammation in your lungs. Bacteria, fungi, animal and plant proteins, and other allergens can cause HP. Acute hypersensitivity pneumonitis can get better, but chronic hypersensitivity pneumonitis can cause irreversible lung damage and scarring.


What is hypersensitivity pneumonitis?

Hypersensitivity pneumonitis (HP) is a type of allergy that causes inflammation in the small air sacs of your lungs (alveoli). Your symptoms can be immediate (acute) and go away quickly, or they may develop over time and become ongoing (chronic).

Chronic hypersensitivity pneumonitis is considered an interstitial lung disease. It can lead to lung scarring over time.

What is the difference between hypersensitivity pneumonitis and other allergies?

Hypersensitivity pneumonitis causes a different immune reaction in your body than pollen or pet allergies. Unlike common allergies that cause hay fever and asthma, repeated exposure to allergens that cause HP can lead to inflammation that can permanently damage your lungs.


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Who does hypersensitivity pneumonitis affect?

You’re at higher risk for hypersensitivity pneumonitis if you work in certain occupations or are around specific allergens. You’re more likely to develop HP if you:

  • Work on a farm (for instance, with cattle or vegetables).
  • Handle animals (veterinarians, bird or poultry handlers).
  • Process and load grains or flour.
  • Work in lumber mills or strip wood.
  • Manufacture wallboard and paper.
  • Are a metal worker.
  • Are around bird droppings or feathers. This includes using feather-filled bedding.
  • Breathe in allergens from humidifiers, heating and air conditioning systems or hot tubs, especially if they aren’t maintained well.
  • Are between 50 and 70 years old.

Is hypersensitivity pneumonitis serious?

Hypersensitivity pneumonitis can be very serious. If you have repeated exposures to allergens that cause HP, the inflammation in your lungs can cause permanent damage.

How does hypersensitivity pneumonitis affect my body?

If you have hypersensitivity pneumonitis, your body overreacts to particles (allergens) you’re breathing in, usually while on the job or in your home. The allergens are small enough to get all the way into the small air sacs in your lungs (alveoli) and cause inflammation.

When you first react to the allergen, your body makes chemicals to recognize it in the future. As you’re exposed to the allergen again and again, your body becomes more sensitized and responds with worsening reactions. Over time, this damages your alveoli and the small airways that lead to them. This causes symptoms like shortness of breath and coughing.


Symptoms and Causes

What are the symptoms of hypersensitivity pneumonitis?

Symptoms of hypersensitivity pneumonitis can be acute or chronic. Acute symptoms come on within a few hours of being around an allergen and last a few hours or days. Chronic symptoms can develop slowly and get worse over time.

Symptoms of acute hypersensitivity pneumonitis

Symptoms of chronic hypersensitivity pneumonitis

What does hypersensitivity pneumonitis feel like?

Acute hypersensitivity pneumonitis might feel like the flu. Chronic HP can develop gradually and may be harder to pinpoint. You might notice that you get short of breath easier than you used to or that you have a cough or fatigue that’s slowly gotten worse.


What causes hypersensitivity pneumonitis?

Breathing in substances (allergens) that create an immune reaction in your lungs causes hypersensitivity pneumonitis. Over time, this can damage your lungs and worsen your symptoms. There are over 300 known causes of hypersensitivity pneumonitis, including:

  • Bacteria.
  • Molds and fungi.
  • Certain chemicals and metals.
  • Animal and plant proteins.

Examples of hypersensitivity pneumonitis

Many allergens cause types of hypersensitivity pneumonitis that go by their own names. Examples of HP include:

Bird fancier’s lung.
Caused by
Proteins in bird feathers or droppings.
Farmer’s lung.
Caused by
Mold that grows on hay, straw and grain.
Hot tub lung.
Caused by
Bacteria in water vapor from hot tubs.
Humidifier lung.
Caused by
Fungi and bacteria in humidifiers and heating and air conditioning systems.
Cheese worker’s lung (or cheese washer’s lung).
Caused by
Fungi on cheese.
Caused by
Sugar cane mold dust.
Mushroom worker’s lung.
Caused by
Dust from fungi.

Does COVID-19 cause hypersensitivity pneumonitis?

COVID-19 isn’t a known cause of hypersensitivity pneumonitis, but it can cause lung inflammation that sometimes looks like HP. There’s also evidence that it may make existing HP worse.

Diagnosis and Tests

How is hypersensitivity pneumonitis diagnosed?

A healthcare provider diagnoses hypersensitivity pneumonitis based on your symptoms and personal history, physical exam and other tests. They may ask you about your work or living environment to understand if you could be exposed to allergens.

Your provider will listen to your lungs with a stethoscope and check your oxygen level with a device they put on your finger (pulse oximeter). You might also get lung function tests, blood tests or imaging.

What tests will be done to diagnose hypersensitivity pneumonitis?

To help diagnose hypersensitivity pneumonitis, your provider might perform or order additional tests, including:

  • Allergy blood tests. A provider takes a small sample of blood from your arm using a needle. A lab tests the sample to see if you have signs of a reaction to the allergens that cause HP (hypersensitivity pneumonitis panel).
  • Imaging. Chest X-rays and CT scans give your provider images of your lungs so they can look for damage.
  • Pulmonary function tests. Most lung function tests involve breathing into a tube attached to a machine to measure how well your lungs are working. Your provider may also do blood tests or exercise tests to check your lung function.
  • Bronchoscopy. A healthcare provider uses a small, flexible tube passed through your nose or mouth to view the inside of your lungs and collect samples.

Management and Treatment

How is hypersensitivity pneumonitis treated?

To successfully treat hypersensitivity pneumonitis, you have to stay away from the cause.

Even with medication, HP won’t go away completely if you continue to breathe in the allergen. Chronic HP causes damage that may get worse even if you aren’t exposed to the allergen anymore.

Your provider may prescribe drugs to reduce inflammation, open your airways or increase your oxygen levels.

What medications/treatments are used for hypersensitivity pneumonitis?

  • Corticosteroids or immunosuppressive medications. These medications help reduce inflammation. Specific drugs could include prednisone, mycophenolate or azathioprine.
  • Anti-fibrotic drugs (pirfenidone and nintedanib). These medications can slow lung scarring.
  • Pulmonary rehabilitation. Breathing exercises and physical therapy can help make breathing easier.
  • Oxygen therapy. If you have severe HP, you may need extra oxygen to make sure your blood or tissues are getting enough. It’s delivered through a mask on your face or a tube in your nose.
  • Lung transplant. If your HP progresses to pulmonary fibrosis, you may need a lung transplant.

How soon after treatment for hypersensitivity pneumonitis will I feel better?

It can take several months for your lungs to heal from the inflammation HP causes. Some damage can be permanent.

How do you get rid of hypersensitivity pneumonitis?

You usually can’t get rid of chronic hypersensitivity pneumonitis. Acute and subacute HP can go away on its own or with medication if you aren’t exposed to the allergen anymore.


How can I prevent hypersensitivity pneumonitis?

The damage chronic HP causes isn’t reversible. The best way to prevent hypersensitivity pneumonitis is by avoiding exposure to allergens that cause lung inflammation. If you have to be around potential allergens, ways you may be able to reduce your risk include:

  • If you have a job that puts you at risk (like working with metal, birds or other animals, lumber, paper, grain and more), wear personal protective equipment (PPE) while working. This includes wearing a mask that filters small particles.
  • Keep humidifiers, hot tubs and heating and cooling systems clean and in good condition.
  • Avoid feather-filled bedding.
  • Keep your pets’ living spaces (especially bird cages) clean. Wear a mask when you clean them.

Outlook / Prognosis

What can I expect if I have hypersensitivity pneumonitis?

What you can expect depends on how long you’ve had hypersensitivity pneumonitis and how severe it is.

Acute HP usually goes away within a few days as long as you don’t get exposed to the allergen again. Subacute cases of HP (caused by longer, low-level exposure to allergens over time) can last a few months and are usually treated with medication. Chronic HP usually doesn’t go away but medication may make your symptoms more manageable.

Complications of hypersensitivity pneumonitis

With continued exposure to an allergen that causes HP, you can have serious complications, including:

Outlook for hypersensitivity pneumonitis

The outlook for chronic hypersensitivity pneumonitis depends on the damage to your lungs. If you don’t have lung scarring, research suggests you can have significant improvement within a year of diagnosis. For those with lung scarring, HP is often fatal within a few years without a lung transplant.

What is the life expectancy of someone with hypersensitivity pneumonitis?

Life expectancy of someone with hypersensitivity pneumonitis depends on the severity of damage to their lungs. A lung transplant can extend your life past these expected timelines.

  • Someone with no scarring (fibrosis) has a life expectancy of greater than 15 years after diagnosis.
  • Someone with fibrosis but no other lung damage, like cysts (honeycombing), has a life expectancy of around eight years after diagnosis.
  • Someone with severe damage — fibrosis and honeycombing — has a life expectancy of around three years after diagnosis.

Living With

How do I take care of myself with hypersensitivity pneumonitis?

If you’ve been diagnosed with hypersensitivity pneumonitis, make a plan with your healthcare provider to reduce the risk of further damage to your lungs. Take all medications as directed by your provider. Ask if there are any physical or breathing exercises you can do at home to improve your lung function.

When should I see my healthcare provider about hypersensitivity pneumonitis?

See a healthcare provider if you have symptoms of hypersensitivity pneumonitis. If you’ve been diagnosed with HP, see your provider for any new or worsening symptoms.

What questions should I ask my doctor?

  • What’s causing hypersensitivity pneumonitis?
  • How can I avoid exposure to the allergen that’s causing HP?
  • Is there damage to my lungs? How severe is it?
  • Is this reversible?
  • How do I take my medications?
  • How long will it take to feel better?
  • When should I follow up with you?

A note from Cleveland Clinic

Hypersensitivity pneumonitis can cause serious lung damage with repeated exposure to an allergen. But if caught early, you can stop the cycle before irreversible damage is done. If you have any ongoing lung symptoms, it’s important to see a healthcare provider right away.

If you’ve been diagnosed with hypersensitivity pneumonitis, have honest discussions with your provider about the severity of your condition. They can help you know what to expect and make a plan to improve your breathing and your quality of life.

Medically Reviewed

Last reviewed on 10/07/2022.

Learn more about our editorial process.

Appointments 216.444.6503