Hypersensitivity Pneumonitis

Last Updated 11/02/2020

Author:Saiprakash Venkateshiah, MD

About Hypersensitivity Pneumonitis

Key facts about Hypersensitivity Pneumonitis
  • Hypersensitivity pneumonitis is caused by being allergic to certain dusts (called allergens) that you breathe in (inhale).
  • This allergy causes inflammation in your lungs.
  • If it is discovered early and you avoid the allergens, then the inflammation can be reversed.
  • Sometimes, hypersensitivity pneumonitis can scar your lungs if it is not discovered early and you keep inhaling the allergens.

Hypersensitivity pneumonitis is caused by an allergy to certain dusts (called allergens) that you breathe in, or inhale. These allergens may be present at home, at work, or in the air. Because they occur naturally, they are called organic. The allergens contain fungus spores (small parts of the fungus) from moldy hay or bird droppings.

If you inhale these allergens, you can get hypersensitivity pneumonitis. You don’t always have the allergy right away: It may take a couple of months or a couple of years to start. Only a few people who inhale these allergens get hypersensitivity pneumonitis.

How Hypersensitivity Pneumonitis affects your body

When you inhale the dust that you are allergic to, you won’t notice any problems the first time. Some people develop symptoms after inhaling a lot the dust all at once or after inhaling small amounts over and over again. Tiny air sacs in the lungs (called alveoli) can become irritated and may fill with fluid. If you stop inhaling the allergen, the irritation can get better in a few days. If you keep inhaling those allergens, the lung irritation continues. Parts of your lung can develop scar tissue. When your lungs have scar tissue, it may be hard to breathe normally.

How serious is Hypersensitivity Pneumonitis?

It’s important to catch this disease early so that you don’t have permanent lung damage:

  • Hypersensitivity pneumonitis can be a serious problem for people whose lungs become scarred.
  • Scarred lungs (also called pulmonary fibrosis) can occur if the disease continues, and it is permanent.
  • Unfortunately, there is no cure or treatment for long-term (or chronic) hypersensitivity pneumonitis.

Symptoms of Hypersensitivity Pneumonitis

Your first symptoms may feel like the flu. The symptoms start about 4 to 6 hours after you breathe in the allergens. The symptoms are:

The first symptoms may last only 12 hours, or they may continue for several days. If you inhale the allergens over and over, you may have these symptoms:

What causes Hypersensitivity Pneumonitis?

There are more than 300 known allergens that, when inhaled as a fine dust, can cause hypersensitivity pneumonitis. Some breathing problems have names based on where the allergen comes from:

  • Farmer’s lung. Seen in farmers and cattle workers, this condition is caused by inhaling mold that grows on hay, straw, and grain.
  • Bird fancier’s lung. Also called pigeon breeder’s disease, this condition is caused by inhaling dust specks from feathers or droppings of many types of birds.
  • Humidifier lung. This condition can develop by inhaling a fungus that grows in humidifiers, air conditioners, and heating systems, especially if they are not cleaned regularly.
  • Hot tub lung. This condition may develop by inhaling germs found in the water mist coming from indoor hot tubs.

What are risk factors for Hypersensitivity Pneumonitis?

If you work in jobs such as the following, you may be more likely to get hypersensitivity pneumonitis:

  • Farmers
  • Vegetable or dairy cattle workers
  • Bird and poultry handlers
  • Veterinarian and animal workers
  • Grain and flour processing and loaders
  • Lumber milling
  • Wood stripping
  • Paper and wallboard makers
  • Inhaling certain chemicals produced in making plastic, painting, and the electronics industry

Most people who work in these jobs don’t get hypersensitivity pneumonitis. If you work in one of these jobs and have a family history, however, you may get the disease.

Diagnosing Hypersensitivity Pneumonitis

Your health care provider will diagnose hypersensitivity pneumonitis by asking you questions about symptoms and doing a physical exam.

Your provider may also order some of the following tests:

  • Chest X-ray and computed tomography (CT) scan. These scans may be able to show early signs of the disease and identify any scars on your lungs.
  • Lung function tests. Lung function tests show how well you breathe to see if your lungs are working correctly.
  • Blood tests. Your provider may order blood tests to find out if you have been exposed to a certain allergen.
  • Bronchoscopy. Your provider may order or perform a bronchoscopy to take images and samples of your lungs. During this procedure, the doctor inserts a small, flexible, pencil-sized tube with a video camera attached (called a bronchoscope) into your nose or mouth and through to your airways.
  • Video-assisted thoracic surgery (VATS) (also called an open lung biopsy). VATS is performed by a heart/lung surgeon to get lung tissue for more testing.
When should you see your health care provider?

If you develop symptoms of hypersensitivity pneumonitis, contact your provider if you have:

  • Flu-like symptoms;
  • Dry cough;
  • Shortness of breath;
  • Tight chest;
  • Fever or chills; or
  • Tiredness 4 to 6 hours after you inhale the allergens.

Flu typically occurs between October and May in North America, but hypersensitivity pneumonitis can happen any time of the year.

Treating Hypersensitivity Pneumonitis

Your health care provider will do a physical exam and listen to your lungs with a stethoscope. People with hypersensitivity pneumonitis may have unusual lung sounds (crackles). Your provider may also use a small tool called a pulse oximeter that goes on your finger to check the amount of oxygen in your blood.

Your provider will ask if you have inhaled any kind of dust at home or at work. Questions your provider may ask include the following:

  • Is there water damage in your home or job from humidifiers, heating systems, or air conditioners?
  • Do you have a hot tub at home?
  • Have you been around bird droppings? Do you have any birds as pets? Do you have any feather cushions or down pillows?

You can bring a friend or family member to the visit: He or she may remember you inhaling certain dusts that you forgot. If the provider can’t figure out where the dust is coming from, a professional (industrial hygienist) who is trained to find such dust may come to your home or job.

The most important thing you can do is not inhale the dust that causes the disease. Your lungs may return to normal. If you can’t stop inhaling the dust, your provider may suggest that you move to a new home or job. If you have bird fancier’s lung, then you may have to give up your pet bird.

If your case is serious, your provider may put you on steroid medication, such as prednisone. You may have to take these medications for up to 3 months and maybe longer. Steroids help with your symptoms, but they will not cure the disease. They also have side effects, such as weight gain, thin bones, eye disease, and abnormal blood sugar levels.

Other medications you may be taking (such as mycophenolate and azathioprine) may keep you from having to take steroids. In rare cases, if you have serious lung scars, you may need a lung transplant.

Managing Hypersensitivity Pneumonitis

Here are suggestions for staying away from certain allergens:

  • Remove any standing water inside and outside your home.
  • Keep the humidity in your home and job below 60%.
  • Repair water damage inside your home or job, including wet carpeting, furniture, and drywall.
  • Make sure your heater and air conditioning are working and that you have good ventilation.
  • Don’t reuse the water in your heater, air conditioner, or ventilation system.
  • If you work with farm products, make sure they are dry when you store them.

Preventing Hypersensitivity Pneumonitis

If you can’t completely avoid the allergens, there are some masks you can try that will help keep you from inhaling them. They cover your nose and mouth and can filter the air you breathe.


The American Lung Association recommends that patients and caregivers join its Living with Lung Disease support community to connect with others facing this disease. To talk to a trained lung professional, call the American Lung Association’s Lung Helpline at 1-800-LUNGUSA. They can help answer your questions and connect you with additional support.

Ask your health care provider about lung disease support groups in your area, or look online for a Better Breathers Club near you.

Questions to Ask Your Health Care Provider

Making notes before your visit and taking along a trusted family member or friend can help you through the first appointment with your doctor. The following are questions you can ask your health care provider:

  • I have hypersensitivity pneumonitis from workplace dust. Is it safe for me to continue working?
  • Are there things I can’t do at work?
  • Do I have to give up my pet birds?
  • Should I stay out of hot tubs?
  • Can my family members get the disease if I have it?
  • What tests will I need to find out if I have hypersensitivity pneumonitis?
  • How often should I get lung function tests?
  • How often should I get chest X-rays and CT scans?
  • Do I need to be on medications (steroids)?
  • Can I use oxygen therapy?
  • Can I still get flu shots and pneumonia shots?
  • Is it okay for me to exercise?
  • Is there a special diet?
  • Is it okay if I fly?