For more information, visit http://www.nhlbi.nih.gov/health/health-topics/topics/hp/

What Is Hypersensitivity Pneumonitis?

Hypersensitivity pneumonitis (noo-mo-NI-tis), or HP, is a disease in which the lungs become inflamed from breathing in foreign substances, such as molds, dusts, and chemicals. These substances also are known as antigens (AN-tih-jens).

People are exposed to antigens at home, while at work, and in other settings. However, most people who breathe in these substances don't develop HP.

Overview

To understand HP, it helps to understand how the lungs work. When you breathe, air passes through your nose and mouth into your windpipe. The air then travels to your lungs' air sacs. These sacs are called alveoli (al-VEE-uhl-eye).

Small blood vessels called capillaries run through the walls of the air sacs. When air reaches the air sacs, the oxygen in the air passes through the air sac walls into the blood in the capillaries. The capillaries connect to a network of arteries and veins that move blood through your body.

In HP, the air sacs become inflamed and may fill with fluid. This makes it harder for oxygen to pass through the air sacs and into the bloodstream.

The two main types of HP are acute (short-term) and chronic (ongoing). Both types can develop as a result of repeatedly breathing in an antigen.

Over time, your lungs can become sensitive to that antigen. If this happens, they'll become inflamed, which can lead to symptoms and may even cause long-term lung damage.

With acute HP, symptoms usually occur within 2–9 hours of exposure to an antigen you're sensitive to. Acute HP can cause chills, body aches, coughing, and chest tightness. After hours or days of no contact with the antigen, symptoms usually go away.

If acute HP isn't found and treated early, chronic HP may develop. Symptoms of chronic HP occur slowly, over months. Chronic HP can cause a worsening cough, shortness of breath with physical activity, fatigue (tiredness), and weight loss. Severe HP may cause clubbing (a widening and rounding of the tips of the fingers or toes).

With chronic HP, symptoms may continue and/or worsen, even after avoiding the antigen. Sometimes, chronic HP can cause long-term lung damage, such as pulmonary fibrosis (PULL-mun-ary fi-BRO-sis). This is a condition in which tissue deep in your lungs becomes scarred over time.

Outlook

Avoiding or reducing your contact with antigens can help prevent and treat HP. For example, cleaning heating and ventilation filters can help reduce your contact with mold. Wetting compost prior to handling it can reduce contact with harmful dust.

If HP is caught early, avoiding the antigen that caused it may be the only treatment you need. If you have chronic HP, your doctor may prescribe medicines to reduce lung inflammation.

Researchers continue to study why some people develop HP after being exposed to antigens, while others don't. They're also looking for better ways to quickly pinpoint which antigens are causing HP in people who are believed to have the disease.

Other Names for Hypersensitivity Pneumonitis

Bird fancier's lung
Extrinsic allergic alveolitis
Farmer's lung
Hot tub lung
Humidifier lung
Mushroom picker's disease

What Causes Hypersensitivity Pneumonitis?

Repeatedly breathing in foreign substances can cause hypersensitivity pneumonitis (HP). Examples of these substances include molds, dusts, and chemicals. (Mold often is the cause of HP.) These substances also are known as antigens.

Over time, your lungs can become sensitive to antigens. If this happens, your lungs will become inflamed, which can lead to symptoms and may even cause long-term lung damage.

Antigens may be found in the home, workplace, or in other settings. Antigens can come from many sources, such as:

Bird droppings
Humidifiers, heating systems, and hot tubs
Liquid chemicals used in the landscaping and florist industries
Moldy hay, straw, and grain
Chemicals released during the production of plastics and electronics, and chemicals released during painting
Mold released during lumber milling, construction, and wood stripping

Who Is At Risk for Hypersensitivity Pneumonitis?

People who repeatedly breathe in foreign substances are at risk for hypersensitivity pneumonitis (HP). These substances, which also are known as antigens, include molds, dusts, and chemicals. However, most people who breathe in these substances don't develop HP.

People at increased risk include:

Farm and dairy cattle workers
People who use hot tubs often
People who are exposed to molds or dusts from humidifiers, heating systems, or wet carpeting
Bird fanciers (people who keep pet birds) and poultry handlers
Florists and landscapers, especially those who use liquid chemicals on lawns and gardens
People who work in grain and flour processing and loading
Lumber milling, construction, wood stripping, and paper and wallboard workers
People who make plastics or electronics, and those who paint or work with other chemicals

What Are the Signs and Symptoms of Hypersensitivity Pneumonitis?

Signs and symptoms of hypersensitivity pneumonitis (HP) depend on whether the disease is acute (short-term) or chronic (ongoing).

Acute Hypersensitivity Pneumonitis

With acute HP, symptoms usually occur within 2–9 hours of exposure to an antigen you're sensitive to. (An antigen is a substance that your body reacts against, such as molds, dusts, and chemicals.)

Acute HP can cause chills, body aches, coughing, and chest tightness. After hours or days of no contact with the antigen, symptoms usually go away.

Chronic Hypersensitivity Pneumonitis

If acute HP isn't found and treated early, chronic HP may develop. With chronic HP, symptoms occur slowly, over months. Chronic HP can cause a worsening cough, shortness of breath with physical activity, fatigue (tiredness), and weight loss.

Some symptoms may continue and/or worsen, even after avoiding the antigen. Chronic HP can cause long-term lung damage, such as pulmonary fibrosis. This is a condition in which tissue deep in your lungs becomes scarred over time.

Clubbing also may occur if HP is severe. Clubbing is the widening and rounding of the tips of the fingers or toes. A low level of oxygen in the blood causes this condition.

How Is Hypersensitivity Pneumonitis Diagnosed?

To diagnose hypersensitivity pneumonitis (HP), your doctor must pinpoint the antigen that's causing the disease and its source. (An antigen is a substance that your body reacts against, such as molds, dusts, and chemicals.)

Your doctor will ask you detailed questions about:

Your current and past jobs
Your hobbies and leisure activities
The types of places where you spend time
Your exposure to damp and moldy places

Your doctor also will do a physical exam and look at test results to diagnose HP.

Physical Exam

During the physical exam, your doctor will ask about your signs and symptoms, such as coughing and weight loss. Your doctor also will look for signs of HP. For example, he or she will listen to your lungs with a stethoscope for abnormal breathing sounds. HP can cause a crackling sound when you breathe.

Your doctor also may look for signs of pulmonary fibrosis, a possible complication of chronic (ongoing) HP. Pulmonary fibrosis is a condition in which tissue deep in your lungs becomes scarred over time.

Your doctor also may check for clubbing. Clubbing is the widening and rounding of the tips of the fingers or toes. A low level of oxygen in the blood causes this condition.

Diagnostic Tests and Procedures

To help diagnose HP, your doctor may recommend or more of the following tests or procedures.

Chest X Ray or Chest Computed Tomography (CT) Scan

A chest x ray and chest CT scan create pictures of the structures inside your chest, such as your heart, lungs, and blood vessels. These pictures can show signs of HP.

Lung Function Tests

Lung function tests measure how much air you can breathe in and out, how fast you can breathe air out, and how well your lungs can deliver oxygen to your blood. One of these tests is spirometry (spi-ROM-eh-tre).

During this test, a technician will ask you to take a deep breath. Then, you'll blow as hard as you can into a tube connected to a small machine. The machine is called a spirometer. The machine measures how much air you breathe out. It also measures how fast you can blow air out.

Pulse Oximetry

This test measures the amount of oxygen in your blood. A small sensor is attached to your finger or ear. The sensor uses light to estimate how much oxygen is in your blood.

Precipitin Test

This blood test looks for antibodies (proteins) that your body creates in response to antigens. The presence of these proteins may suggest HP.

Challenge Test

During this test, you're re-exposed to the suspected antigen. Then, you'll be watched for signs and symptoms of HP.

Bronchoscopy

For bronchoscopy (bron-KOS-ko-pee), your doctor passes a thin, flexible tube through your nose (or sometimes your mouth), down your throat, and into your airways. At the tip of the tube are a light and mini-camera. This allows your doctor to see your windpipe and airways.

Your doctor may insert forceps (a device used to grab or hold things) through the tube to collect a tissue sample. You'll be given medicine to make you relaxed and sleepy during the procedure.

Bronchoalveolar Lavage

During bronchoscopy, your doctor may inject a small amount of salt water (saline) through the tube into your lungs. This method is called bronchoalveolar lavage (BRONG-ko-al-VE-o-lar lah-VAHZH).

This fluid washes the lungs and helps bring up cells from the airways and the area around the air sacs. Your doctor will look at these cells under a microscope.

Surgical Lung Biopsy

To confirm a diagnosis of HP, your doctor may do a surgical lung biopsy. Your doctor can use a biopsy to rule out other causes of symptoms and check the condition of your lungs.

For a surgical lung biopsy, your doctor takes samples of lung tissue from several places in your lungs. He or she then looks at them under a microscope. Your doctor may use one of the following methods to get lung tissue samples.

Video-assisted thoracoscopy (thor-ah-KOS-ko-pee). For this procedure, your doctor inserts a small, lighted tube with a camera (endoscope) into your chest through small cuts between your ribs.

The endoscope provides a video image of your lungs and allows your doctor to collect tissue samples. This procedure is done in a hospital. You'll be given medicine to help you sleep through the procedure.

Thoracotomy (thor-ah-KOT-o-me). For this procedure, your doctor removes a few small pieces of lung tissue through a cut in the chest wall between your ribs. Thoracotomy is done in a hospital. You'll be given medicine to help you sleep through the procedure.

How Is Hypersensitivity Pneumonitis Treated?

The best way to treat hypersensitivity pneumonitis (HP) is to avoid the antigen that caused it. (An antigen is a substance that your body reacts against, such as molds, dusts, and chemicals.)

In acute (short-term) HP, symptoms usually go away once you're no longer in contact with the antigen. In chronic (ongoing) HP, you may need medicines to relieve your symptoms.

People who have chronic HP may develop pulmonary fibrosis. This is a condition in which tissue deep in your lungs becomes scarred over time. People who have this condition may need further treatment, such as oxygen therapy and pulmonary rehabilitation (rehab).

Avoiding Antigens

Once the antigen that caused the HP and its source are found, you can take steps to avoid it. If HP is caught early, avoiding the antigen may be the only treatment you need.

Avoiding an antigen may be easier at home than at work. For example, if your pet bird, moldy carpet, or hot tub is the source of the antigen, you can remove it from your home. If your heating system is the source of the antigen, you can have your system properly serviced.

However, if the antigen is at work, you may need to talk with your supervisor about your condition and ways to protect yourself. For example, masks or personal respirators may help protect you from antigens in the air. (A personal respirator is a device that helps filter the air you breathe in.)

Some people who have HP may need to move to a different home or change jobs to avoid antigens. After hurricanes, for example, some people have to move from their homes to avoid molds that could harm their lungs. However, moving and changing jobs sometimes isn't possible.

Medicines and Other Treatments

If you have chronic HP, your doctor may prescribe medicines called corticosteroids. These medicines reduce lung inflammation. Prednisone is an example of a corticosteroid.

Long-term use of prednisone, especially at high doses, can cause serious side effects. Thus, if your doctor prescribes this medicine, he or she may reduce the dose over time.

Examples of side effects from corticosteroids are increased risk of infections, high blood pressure, high blood sugar, and osteoporosis (thinning of the skin and bones).

People who develop pulmonary fibrosis may need medicines, oxygen therapy, and/or pulmonary rehab. Pulmonary fibrosis is a condition in which tissue deep in your lungs becomes scarred over time.

If you smoke, try to quit. Smoking can make HP symptoms worse and lead to other lung diseases. Talk with your doctor about programs and products that can help you quit. Also, try to avoid secondhand smoke.

Living With Hypersensitivity Pneumonitis

If you've had hypersensitivity pneumonitis (HP), avoiding the antigen that caused it is important. (An antigen is a substance that your body reacts against, such as molds, dusts, and chemicals.)

If HP is caught early, your symptoms will likely go away if you avoid contact with the antigen. Continued contact with the antigen can make your symptoms worse and may lead to long-term lung damage.

To avoid the antigen, you may need to find other hobbies, change jobs, move, or use protective gear (like a mask) at work.

If you smoke, try to quit. Smoking can make HP symptoms worse and lead to other lung diseases. Talk with your doctor about programs and products that can help you quit smoking. Also, try to avoid secondhand smoke. Ask family members, friends, and coworkers not to smoke in front of you or in your home, car, or workplace.

If you've developed pulmonary fibrosis from the HP, you'll need further ongoing care. Pulmonary fibrosis is a condition in which tissue deep in your lungs becomes scarred over time.

If you have this condition, you may need medicines, oxygen therapy, and/or pulmonary rehabilitation. Follow your treatment plan as your doctor advises.

Clinical Trials

The National Heart, Lung, and Blood Institute (NHLBI) is strongly committed to supporting research aimed at preventing and treating heart, lung, and blood diseases and conditions and sleep disorders.

NHLBI-supported research has led to many advances in medical knowledge and care. Often, these advances depend on the willingness of volunteers to take part in clinical trials.

Clinical trials test new ways to prevent, diagnose, or treat various diseases and conditions. For example, new treatments for a disease or condition (such as medicines, medical devices, surgeries, or procedures) are tested in volunteers who have the illness. Testing shows whether a treatment is safe and effective in humans before it is made available for widespread use.

By taking part in a clinical trial, you can gain access to new treatments before they're widely available. You also will have the support of a team of health care providers, who will likely monitor your health closely. Even if you don't directly benefit from the results of a clinical trial, the information gathered can help others and add to scientific knowledge.

If you volunteer for a clinical trial, the research will be explained to you in detail. You'll learn about treatments and tests you may receive, and the benefits and risks they may pose. You'll also be given a chance to ask questions about the research. This process is called informed consent.

If you agree to take part in the trial, you'll be asked to sign an informed consent form. This form is not a contract. You have the right to withdraw from a study at any time, for any reason. Also, you have the right to learn about new risks or findings that emerge during the trial.

For more information about clinical trials related to hypersensitivity pneumonitis, talk with your doctor. You also can visit the following Web sites to learn more about clinical research and to search for clinical trials:

For more information about clinical trials for children, visit the NHLBI's Children and Clinical Studies Web page.

Links to Other Information About Hypersensitivity Pneumonitis

NHLBI Resources

Cough (Health Topics)
How the Lungs Work (Health Topics)

Non-NHLBI Resources

Hypersensitivity Pneumonitis (MedlinePlus)

Clinical Trials

Children and Clinical Studies
Clinical Trials (Health Topics)
Current Research (ClinicalTrials.gov)
NHLBI Clinical Trials
NIH Clinical Research Trials and You (National Institutes of Health)
ResearchMatch (funded by the National Institutes of Health)