What Is Hypersensitivity Pneumonitis?

Medically Reviewed by Minesh Khatri, MD on September 18, 2022
4 min read

You may not think it's a big deal when you breathe in dust, but for some people, it could bring on a lung disease called hypersensitivity pneumonitis. It's an allergic reaction to particles in the dust, and it can cause symptoms like coughing and shortness of breath. You can get things back to normal if you get treated early and avoid breathing the stuff you're allergic to.

There are a variety of things that can cause hypersensitivity pneumonitis when you breathe them in, including fungus, molds, bacteria, proteins, and chemicals.

Normally, the immune system -- your body's defense against germs -- causes inflammation in your lungs as it clears away the things you're allergic to. After a while, the inflammation stops. But in some people who are "hypersensitive," the lungs stay inflamed and cause the symptoms of hypersensitivity pneumonitis.

If you catch it early and stop breathing in more particles, your lungs can heal. If you breathe them in over and over, your lungs will stay inflamed, and scars may develop, which can make it hard to breathe normally.

It's hard to tell how many people have hypersensitivity pneumonitis because many don't get diagnosed or are mistakenly thought to have another lung disease, like asthma.

You can breathe in troublesome particles in your home, at work, or almost any other place you usually go. It may take months or years before you become allergic to them.

Some sources of particles that can cause hypersensitivity pneumonitis include:

  • Animal fur
  • Fungus that grows in air conditioners, humidifiers, and heating systems
  • Bird droppings and feathers
  • Mold that grows on hay, straw, or grain animal feed
  • Bacteria in water vapor from hot tubs

You may be more likely to get hypersensitivity pneumonitis if you have a job that puts you in contact with these particles, like farming, veterinary work, and lumber mill operations. But most people who breathe them in won't get the lung disease, so experts think certain genes play a role.

To find out if you have hypersensitivity pneumonitis, your doctor will want to know about the kinds of dust you may have been in contact with. They'll ask you questions like:

  • Do you have any pet birds?
  • Do you have a hot tub?
  • Have you been around any water damage, especially from a humidifier, heater, or air conditioner?

Your answers to these questions will also help your doctor figure out the best treatment.

Your doctor will also listen for abnormal sounds in your lungs and will check the oxygen levels in your blood. You may also get tests like:

  • Blood tests
  • Chest X-ray or CT scan
  • Tests to see how well your lungs are working
  • Lung biopsy (removing a small piece of lung tissue)


There are three types, based on how long you have had the disease and how severe your symptoms are.

Acute. This type is brief and severe. It feels like you caught the flu, and it happens after you've been around a lot of dust. Your symptoms should get better in a couple of days if you don't breathe in any more dust but will probably return if you do. Your symptoms could include:

You might have these symptoms from 12 hours to several days.

Subacute. It can happen when you have low-level contact with the dust over time. It may start out with a fever. Then shortness of breath, tiredness, and coughing can start over weeks or months. This type of hypersensitivity pneumonitis tends to get worse with time.

Chronic. This is a long-lasting form that happens after a low but long period of contact with dust. You may get symptoms like shortness of breath, tiredness, coughing, and weight loss that slowly get worse. This kind of hypersensitivity pneumonitis can lead to permanent lung scarring.

The most important thing you can do is avoid the dust that caused your hypersensitivity pneumonitis. If you have a chronic form of the disease, you may take a steroid medicine to help curb inflammation. They have side effects like weight gain and higher blood sugar.

Early studies suggest that drugs that curb the immune system -- like azathioprine (Imuran) or rituximab (Rituxan) -- may be helpful. More research is needed.

You may also go to pulmonary rehab, a program that helps people with breathing problems improve their health.

If you're having a lot of trouble breathing, you may need to get extra oxygen through a mask or tubing. Some people need oxygen all the time, while others just need it when they exercise or sleep.

For some people who have a lot of scarring in their lungs, a lung transplant may be the best option.

There are lots of things you can do to be your healthiest with hypersensitivity pneumonitis.

  • Make sure to go to all doctor's appointments so you can get the right treatment for any symptoms, such as tiredness or breathing problems.
  • Get all your vaccines, especially the flu shot, to avoid infections that can hurt your lungs.
  • Get some exercise, but talk to your doctor about which activities are right for you and any you should avoid.
  • Quit smoking. It makes the disease worse, especially the chronic type.