Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is lung inflammation that happens when you breathe in certain substances. It can cause flu-like symptoms that come and go when you’re around things like bird droppings, water vapor contaminated with bacteria or mold spores, or dust from certain types of foods. Or it can start with mild symptoms that get worse over time, like a chronic cough or worsening shortness of breath.

Most people don’t have reactions to the substances that cause HP. But for people who do, it can cause serious lung damage over time.

Hypersensitivity pneumonitis (pronounced “HI-per-sen-si-TIV-it-ee new-muhn-EYE-tis”) can be fibrotic or non-fibrotic. Fibrotic HP causes irreversible lung scarring. It’s a form of interstitial lung disease. Non-fibrotic HP causes inflammation without scarring. It can eventually lead to lung scarring if you continue to be exposed to the substance that causes inflammation.

Types

There are many different types of hypersensitivity pneumonitis. They often get their names from what triggers the inflammation. Below are some examples of types and their causes:

• Bagassosis: Sugar cane mold dust
• Bird fancier’s lung: Proteins in bird feathers or droppings
• Cheese worker’s lung/cheese washer’s lung: Fungi on cheese
• 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
• Mushroom worker’s lung: Dust from fungi

Symptoms of hypersensitivity pneumonitis

Symptoms include:

• Shortness of breath
• Dry cough
• Chest tightness
• Chills
• Fatigue
• Fever
• Muscle aches

Symptoms can come on within a few hours of being around a substance that triggers inflammation. They might last a few hours or days. Over time, with repeated or long-term exposure to triggers, you might have:

• Shortness of breath, especially with exertion or activity
• Chronic cough
• Fatigue that gets worse over time
• Weight loss
• Finger or toe clubbing

Hypersensitivity pneumonitis causes

An immune reaction in your lungs causes hypersensitivity pneumonitis. It happens when your body thinks certain substances you breathe in are harmful. Your immune system causes inflammation to try to fight off the substance, or trigger.

If you’re exposed to a trigger over and over again, your body becomes more sensitized and responds with worsening reactions. Over time, this can damage the air sacs in your lungs (alveoli) and the small airways that lead to them.

There are over 300 known specific causes of hypersensitivity pneumonitis. These include:

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

But most people don’t react to these substances. Studies suggest that genetics may play a role in whether you react and whether you’ll develop scarring.

Risk factors

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

• Work on a farm (for instance, with cattle, hay or vegetables)
• Handle animals (for example, if you're a veterinarian or a bird or poultry handler)
• 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, including feather-filled bedding
• Work around humidifiers, heating and air conditioning systems, or hot tubs, especially if they aren’t maintained well

HP is more common in people between 50 and 70 years old.

Complications

Repeated or long-term inflammation from HP can cause:

• Scarring in your lungs (pulmonary fibrosis)
• High blood pressure between your heart and lungs (pulmonary hypertension)

How doctors diagnose hypersensitivity pneumonitis

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

To help diagnose HP, your provider might recommend:

• Blood tests: A hypersensitivity pneumonitis panel is a type of blood test that looks for IgG antibodies to substances that can cause inflammation.
• 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 passes a small, flexible tube through your nose or mouth to view the inside of your lungs and collect samples.

How is hypersensitivity pneumonitis treated?

Hypersensitivity pneumonitis doesn’t go away on its own. To avoid further inflammation, you have to stay away from the cause or trigger. Fibrotic HP causes damage that may get worse even if you avoid the trigger.

Your provider may prescribe medications or other treatments. These can help your symptoms but won’t cure HP or prevent further inflammation or damage. These include:

• Corticosteroids or immunosuppressive medications: These help reduce inflammation.
• Antifibrotic medications (pirfenidone and nintedanib): These 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.
• Lung transplant: If HP progresses to pulmonary fibrosis, you may be eligible for a lung transplant.

When should I see my healthcare provider?

See a healthcare provider if you have a long-lasting cough, shortness of breath or other HP symptoms. If you’ve been diagnosed with HP, see your provider for any new or worsening symptoms.

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. Flu-like symptoms can go away within a few days if you’re not around the trigger anymore. It can take several months to a year for inflammation to heal. You may need medication to ease some symptoms.

Some lung damage may be permanent. It could get worse over time, even if you avoid any triggers. Medications might slow down scarring and help you manage symptoms.

What’s the life expectancy for hypersensitivity pneumonitis?

Life expectancy for someone with hypersensitivity pneumonitis depends on the type and severity of damage to your lungs, as well as the initial trigger:

• If you have no scarring and avoid what triggered HP, the condition shouldn’t change your life expectancy.
• If you have scarring but no other lung damage, like cysts (honeycombing), average life expectancy is around eight years after diagnosis.
• If you have severe damage, like fibrosis and honeycombing, average life expectancy may be as little as three years after diagnosis.

A lung transplant may extend your life past these expected timelines, but only if you have more severe damage.

Can HP be prevented?

The best way to prevent hypersensitivity pneumonitis is to avoid exposure to substances that cause lung inflammation. If you can't avoid potential triggers, taking these steps may reduce your risk:

• Wear personal protective equipment (PPE) while working around potential triggers. 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 and clothing.
• Keep your pets’ living spaces (especially bird cages) clean. Wear a mask when you clean them.

What’s the difference between hypersensitivity pneumonitis and allergies?

Hypersensitivity pneumonitis causes a different immune reaction in your body than allergies. Common allergies, like pet and pollen allergies, may cause lung inflammation, like asthma. But they don’t lead to irreversible scarring. Repeated exposure to HP triggers can permanently scar your lungs.