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Hypersensitivity pneumonitis (HP)
Hypersensitivity pneumonitis is a rare disease that can cause a build-up of scarring in the lungs
Hypersensitivity pneumonitis is a rare interstitial lung disease (ILD) that affects only 2-3 people in 100,000 each year.1 However, there are certain individuals with a much higher likelihood of developing this disease based on substances they are exposed to (e.g., certain farmers and bird breeders).
Hypersensitivity pneumonitis occurs in people when the body’s immune system overreacts in response to foreign substances, known as antigens, that they have breathed in. These antigens can include infectious organisms in mouldy hay or contaminated hot tubs, proteins from bird feathers or droppings, or tiny chemicals used in for example, plastics manufacturing or certain types of spray paint. These are just a few examples from hundreds of different substances where prolonged exposure can lead to inflammation in the lungs, known as pneumonitis.2,3
Pulmonary fibrosis in hypersensitivity pneumonitis only occurs in some people with repeated exposure to the antigen. After early exposure, individuals often have fever and sore muscles/joints. Eventually they may develop cough and, less commonly, shortness of breath. After exposure to an antigen, symptoms can resolve if there is complete avoidance of the triggering antigen (allergen). This is known as acute hypersensitivity pneumonitis.
In cases of repeated exposure to the allergen, the symptoms don’t go away. This is known as chronic hypersensitivity pneumonitis, and is often associated with pulmonary (lung) scarring (fibrosis).2 This scar tissue affects the transfer of oxygen from the tiny air sacs (alveoli) of the lung to the blood vessels responsible for providing oxygen to all parts of the body. As healthy lung tissue is replaced by scar tissue, it becomes harder for oxygen to pass through the lungs and into the bloodstream. This results in shortness of breath.4
Know your risk
Sometimes the antigen leading to chronic hypersensitivity pneumonitis isn’t identified. Other factors, such as some viral infections, medications and genetics may increase the risk of chronic hypersensitivity pneumonitis. It is not yet established why some people get chronic hypersensitivity pneumonitis and others don’t.2,3
Watch a short video about the signs, symptoms and risk factors of chronic hypersensitivity pneumonitis.
Download our booklet for an overview about living with pulmonary fibrosis.
You may also find our page ‘What is pulmonary fibrosis’ useful.
How can we support you?
On this page you can find information that may help if you:
Think you may be at risk of or have chronic hypersensitivity pneumonitis but don’t yet have a confirmed diagnosis
Have been diagnosed with chronic hypersensitivity pneumonitis and want to know more about it
I think I may be at risk of chronic hypersensitivity pneumonitis… what should I do?
Chronic hypersensitivity pneumonitis is rare so it is unlikely that you will be affected. However, if you do have risk factors for developing chronic hypersensitivity pneumonitis, it’s always best to ask your doctor for a lung examination to rule it out. You might consider asking:
Does my job or lifestyle put me at risk of chronic hypersensitivity pneumonitis?
Could my symptoms be related to chronic hypersensitivity pneumonitis?
What breathing tests and scans can you offer to diagnose chronic hypersensitivity pneumonitis?
There are a variety of symptoms you may experience with chronic hypersensitivity pneumonitis. These may be less obvious at first and gradually become more noticeable.5,6 These symptoms include:
Cough
Shortness of breath, especially with mild physical activity
Feeling very tired when going about your normal day
Some individuals experience weight loss
These symptoms may arise from other causes, and do not necessarily mean you have chronic hypersensitivity pneumonitis, but keeping a diary of them may help a conversation with your healthcare professional if you're concerned.
Symptoms can also vary from one person to another, so your symptoms may not be the same as somebody else who has chronic hypersensitivity pneumonitis.3
The earlier chronic hypersensitivity pneumonitis is diagnosed, the sooner you can get support and your doctor can decide the best way forward for you.
Talking to your healthcare professional about your symptoms
You and your healthcare professional may find it helpful to keep a record of any chronic hypersensitivity pneumonitis symptoms you may have been experiencing. Take note of:
Has anything changed in your work or home environment?
Do your symptoms get worse or better depending on where you are or what you are doing at the time?
How long do your symptoms last and how often do you experience them?
Could you be allergic to something?
If you have identified what triggers your allergic reaction, talk to your doctor or nurse about steps you can take to avoid or eliminate direct contact with the allergen. If you manage to get an early diagnosis and stay away from the triggering allergen, it is possible that your lungs may gradually return to normal.7
IMPORTANT
If a specific allergen is identified as a cause, it is important to completely avoid exposure to it. It might help to speak with your employer to find out what steps they can take to help you with this in the workplace
QUICK TIP
Keep a diary of your symptoms to track how you feel over time. Also, make a note of any questions and be sure to share your symptoms with your doctor or nurse
Monitoring symptoms
When diagnosing chronic hypersensitivity pneumonitis, your treatment team will look at many areas of your health. For example, they will ask you about your home and work environment, family medical history, medications that you are taking, and whether you smoke or have ever smoked.
A physical examination is also used to give the doctor a better understanding of your lung health. However, other tests, particularly breathing tests and X-rays or CT scans, will be needed to make a clear diagnosis.3
Waiting for and receiving a diagnosis of chronic hypersensitivity pneumonitis can feel confusing, and frustrating;8 however, pushing for an early diagnosis and management of chronic hypersensitivity pneumonitis is important, to give your lungs a chance of recovering.9 Your nurse would be a helpful source of support when it comes to symptom management, lifestyle changes, and first point of contact if you have any questions.
In more severe chronic hypersensitivity pneumonitis, in addition to avoiding the allergen, you may need treatment to help with your breathing.7 Ask your doctor about your treatment options, including pulmonary rehabilitation, which could help you manage your condition.
For some people with chronic hypersensitivity pneumonitis, symptoms may not fully resolve, and research suggests that they live for about 7 years if this is the case.2,6 Some people might face progression of the disease, which means over time, symptoms and how well your lungs work might get worse, or the HRCT scan may show that fibrosis in the lungs has increased. However, currently there is no way of predicting if, or how fast, this will happen. Some people may not have changes in their symptoms, while others may experience a faster worsening of their symptoms. It is not known why some people’s disease progresses faster than others.3,6
It’s important that your healthcare professional checks your lung health regularly so that any changes can be managed quickly.
Keeping your home and work environment well-ventilated can help keep the air clean and reduce dampness. This is important, because dampness can create an environment for mould to grow, which can trigger allergic reactions.10
There are other changes you can make to your home and environment to help take care of your lungs. Take steps to limit your exposure to certain dusts both at home and in your workplace:7
Bacteria and fungus can thrive in stagnant, or still water, so be sure to remove any standing water inside and outside of your home
Try to keep the humidity in your home and workplace below 50 percent
Make sure your heating, ventilation and air conditioning systems are properly maintained
Ask a loved one or your workplace to repair any water damage at home or at work. This includes carpets, furniture and drywall
If you work with farm products, make sure to properly dry and store them
Speak to your treatment team for guidance on how to speak with your employer about changes you may need to make to your workplace. They’ll be best able to advise you and give helpful suggestions.
You can get involved in managing your condition by:
Communicating promptly – let your healthcare professional know how the chronic hypersensitivity pneumonitis treatment is going for you, to ensure you are on the right track to prevent disease progression
Discussing your medical history, symptoms, and allergies with your healthcare professional
Reporting new and existing symptoms – let your healthcare professional know if they are getting any better or worse
Reporting any adverse effects from treatment – let your healthcare professional know how it is affecting you
Attending review appointments to monitor treatment
Practical advice
Your mental wellbeing
“Join a support group, if somebody puts out a hand for help, somebody will always hold it”
Key takeaways
Hypersensitivity pneumonitis occurs when the body’s immune system overreacts and develops an allergic reaction after breathing in certain substances or allergens in the environment
In chronic hypersensitivity pneumonitis, the lungs might become scarred making it harder for oxygen to enter the blood resulting in shortness of breath
If you have risk factors for developing chronic hypersensitivity pneumonitis or are experiencing symptoms –ask your doctor for a lung examination as soon as you can
It is important to completely avoid exposure to the allergen as continued exposure might result in progression of the disease
Fernández Pérez E, Kong A, Raimundo K, et al. Epidemiology of Hypersensitivity Pneumonitis among an Insured Population in the United States: A Claims-based Cohort Analysis. Ann Am Thorac Soc. 2018;15(4):460–469.
Asthma + Lung UK. Pulmonary Fibrosis: Hypersensitivity Pneumonitis. Available at: https://www.asthmaandlung.org.uk/conditions/pulmonary-fibrosis/hypersensitivity-pneumonitis [Accessed July 2023].
National Heart, Lung, and Blood Institute. Hypersensitivity Pneumonitis. Available at: https://www.nhlbi.nih.gov/health-topics/hypersensitivity-pneumonitis [Accessed July 2023].
Asthma + Lung UK. What is pulmonary fibrosis? Available at: https://www.asthmaandlung.org.uk/conditions/pulmonary-fibrosis/what-pulmonary-fibrosis [Accessed July 2023].
Salisbury ML, Myers JL, Belloli EA, et al. Diagnosis and Treatment of Fibrotic Hypersensitivity Pneumonia. Where We Stand and Where We Need to Go. Am J Respir Crit Care Med. 2017;196(6):690–699.
Vasakova M, Morell F, Walsh S, et al. Hypersensitivity Pneumonitis: Perspectives in Diagnosis and Management. Am J Respir Crit Care Med. 2017;196(6):680–689.
American Lung Association. Treating and managing hypersensitivity pneumonitis. Available at: https://www.lung.org/lung-health-diseases/lung-disease-lookup/hypersensitivity-pneumonitis/treating-and-managing [Accessed July 2023].
Aronson KI, Hayward BJ, Robbins L, et al. ‘It’s difficult, it’s life changing what happens to you’ patient perspective on life with chronic hypersensitivity pneumonitis: a qualitative study. BMJ Open Resp Res. 2019;6:e000522.
Riario GG and Marinou A. Hypersensitivity pneumonitis: a complex lung disease. Clin Mol Allergy. 2017;15:6.
Barnes H, Troy L, Lee, CT, et al. Hypersensitivity pneumonitis: Current concepts in pathogenesis, diagnosis, and treatment. Allergy. 2022;77:442–453.
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