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.
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.
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.
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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:
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.
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 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.
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.
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:
Many allergens cause types of hypersensitivity pneumonitis that go by their own names. Examples of HP include:
|Bird fancier’s lung.||Proteins in bird feathers or droppings.|
|Farmer’s lung.||Mold that grows on hay, straw and grain.|
|Hot tub lung.||Bacteria in water vapor from hot tubs.|
|Humidifier lung.||Fungi and bacteria in humidifiers and heating and air conditioning systems.|
|Cheese worker’s lung (or cheese washer’s lung).||Fungi on cheese.|
|Bagassosis.||Sugar cane mold dust.|
|Mushroom worker’s lung.||Dust from fungi.|
|Bird fancier’s lung.|
|Proteins in bird feathers or droppings.|
|Mold that grows on hay, straw and grain.|
|Hot tub lung.|
|Bacteria in water vapor from hot tubs.|
|Fungi and bacteria in humidifiers and heating and air conditioning systems.|
|Cheese worker’s lung (or cheese washer’s lung).|
|Fungi on cheese.|
|Sugar cane mold dust.|
|Mushroom worker’s lung.|
|Dust from fungi.|
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.
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.
To help diagnose hypersensitivity pneumonitis, your provider might perform or order additional tests, including:
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.
It can take several months for your lungs to heal from the inflammation HP causes. Some damage can be permanent.
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.
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:
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.
With continued exposure to an allergen that causes HP, you can have serious complications, including:
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.
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.
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.
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.
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.
Last reviewed by a Cleveland Clinic medical professional on 10/07/2022.
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