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Pulmonary fibrosis

Hypersensitivity pneumonitis

This page is about hypersensitivity pneumonitis (HP), a form of pulmonary fibrosis. We explain how it can be caused, the symptoms and treatment options that are available.

What is hypersensitivity pneumonitis?

Hypersensitivity pneumonitis (HP) happens if your lungs develop an immune response – hypersensitivity - to something you breathe in which results in inflammation of the lung tissue - pneumonitis. It used to be called extrinsic allergic alveolitis (EAA).

One example is farmer’s lung. This is caused by breathing in mould that grows on hay, straw and grain. Another is bird fancier’s lung, caused by breathing in particles from feathers or bird droppings. It can be very difficult to find the exact cause of hypersensitivity pneumonitis.

What are the symptoms of hypersensitivity pneumonitis?

The symptoms, including coughing, shortness of breath, and sometimes fever and joint pains can come on suddenly after you’ve been exposed. This is the acute (short-term) form of the condition. It can go away - without leading to fibrosis (scarring) of the lung - if you can permanently avoid the substance that caused the attack.

In other cases, symptoms of breathlessness and cough may only appear more gradually, perhaps over many years, as a result of permanent scarring of the lungs. This is called chronic (long-term) hypersensitivity pneumonitis and often a specific cause cannot be found. 

How is hypersensitivity pneumonitis treated?

Hypersensitivity pneumonitis is regarded as a more treatable cause of pulmonary fibrosis, but it can cause symptoms that get worse over time and become hard to treat.

If a specific cause is identified, it’s really important to completely avoid exposure to it.

You may need to take anti-inflammatory medication called steroids for a few weeks or months. If you need steroids to control the condition for longer, your doctor may recommend more drugs to reduce the risk of side effects associated with steroids.

 “I may never know what’s causing my condition”

Jane, 61, was first diagnosed with hypersensitivity pneumonitis 10 years ago.

When I moved to London, I developed a cough. It got so bad I ended up in hospital and was diagnosed with hypersensitivity pneumonitis. I took high dose steroids – and my symptoms disappeared! For seven years I had no symptoms at all. 

But when the symptoms came back, they didn’t go away. So now my hypersensitivity pneumonitis is long-term. Tests showed I have a hypersensitivity to pigeon and budgie droppings, but my doctor says there are thousands of other things that I could be reacting to. I may never know what’s causing my condition.

I get unpleasant bouts of coughing. And small things make me tired – like carrying shopping home. 

I found my work as a lawyer more and more difficult. My employers suggested I claim on their permanent health insurance policy. My claim was accepted and I’m now on long-term sick leave.

I take steroids and immune-suppressing drugs every day. I’ll probably take drugs for the rest of my life.

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Last medically reviewed: June 2022. Due for review: June 2025

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.