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. Many other substances can cause similar disease patterns. In many cases it can be very difficult to find the exact cause.


The symptoms include cough, shortness of breath and sometimes fever and joint pains. They can come on suddenly after you’ve been exposed. This is called acute HP. It goes away – without leading to fibrosis of the lung – if you can recognise and completely avoid the substance that caused the attack. Other people may get symptoms of breathlessness and cough more gradually, perhaps over many years, because their lungs are permanently scarred. This is called chronic, or long-term, HP. Often a specific cause cannot be found.


HP is regarded as a more treatable cause of pulmonary fibrosis, but it can cause progressive symptoms 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 a small things makes 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.