Hypersensitivity pneumonitis is a rare immune system disorder that affects your lungs. This disease is also called bird fancier’s lung, extrinsic allergic alveolitis, farmer’s lung, hot tub lung, or humidifier lung.
Hypersensitivity pneumonitis happens in some people after they breathe in certain substances in the environment, such as mold or the skin cells shed by animals with fur. These substances trigger the immune system and cause short- or long-term inflammation in the lungs. This inflammation prevents the lungs from working properly and can make it harder to breathe.
Some types of hypersensitivity pneumonitis can be treated by avoiding the substance that is causing the condition or with medicines. Without treatment, hypersensitivity pneumonitis can cause permanent damage to the lungs.
What are the symptoms?
Symptoms of hypersensitivity pneumonitis can develop quickly or slowly and worsen over months or years. Also, your symptoms may suddenly get worse from time to time. Possible symptoms include:
- Shortness of breath
- Abnormal sounds when you breathe (called rales)
- Flu-like illness, including fever, chills, muscle or joint pain, or headaches, often starting soon after you breathe in the substance that causes your condition
- Chest pain
- Extreme tiredness
- Long-term bronchitis
- Weight loss
- Clubbing, a widening and rounding at the ends of your fingers or toes, along with a downward sloping of the nails
How is it diagnosed?
Your healthcare provider will diagnose hypersensitivity pneumonitis based on your medical history, symptoms, a physical exam, and results from lung tests and blood tests. You may also need one of the following tests:
- Inhalation challenge tests show whether you develop symptoms when you breathe in a specific substance.
- Precipitin tests check for antibodies in your blood that recognize and bind to a specific substance. If you have antibodies to a substance, your healthcare provider may use an inhalation challenge test to confirm that this substance is causing your symptoms.
What causes it?
Hypersensitivity pneumonitis can happen when you repeatedly breathe in bacteria, mold, or chemicals in your environment that cause inflammation in your lungs.
These harmful substances may be found in:
- Air conditioners, humidifiers, and ventilation systems
- Bird droppings, feathers, and animal furs
- Contaminated foods or factory products
- Contaminated fluids from metal work
- Hardwood dusts
- Hay or grain for feeding animals
- Hot tubs
If you have hypersensitivity pneumonitis, your body’s immune system reacts strongly to these substances. Differences in our immune systems may explain why some people have strong reactions after breathing in certain substances while others do not.
What raises the risk of hypersensitivity pneumonitis?
A number of factors raise your risk of hypersensitivity pneumonitis, including:
- Age: Hypersensitivity pneumonitis can happen at any age, but people often are diagnosed with this condition when they are between 50 and 70 years old. Hypersensitivity pneumonitis is also a common type of long-term interstitial lung disease in children.
- Environment or occupation: People in certain occupations have a higher risk of being exposed to substances that can cause hypersensitivity pneumonitis. This includes farmers or people who breed animals or birds, people who work with harsh chemicals, woodworkers, and wine makers.
- Family history: Your genes can control whether you have a strong response to substances in your environment. You may have a higher risk of hypersensitivity pneumonitis if someone in your family has this condition or another ILD.
- Lifestyle habits: Having pets such as birds in your home can raise your risk of hypersensitivity pneumonitis.
- Other medical conditions: Some viral infections in older adults may raise the risk of developing hypersensitivity pneumonitis.
How is it treated?
If you have hypersensitivity pneumonitis, treatment can help prevent lung scarring and can improve your symptoms.
The first step in treatment is often avoiding the bacteria, chemical, or other substance that caused your condition. Sometimes, you may not know what is causing it.
You may also need one or more of the following treatments:
- Medicines to calm your immune system or relax the muscles in your airways to help you breathe easier
- Pulmonary rehabilitation to learn how to breathe easier to improve your quality of life
- Oxygen therapy if you have low levels of oxygen in your blood
- Lung transplant if your lungs are seriously damaged and no other treatment option works for you
Without proper treatment, hypersensitivity pneumonitis can lead to pulmonary hypertension, permanent lung damage, or heart failure.
How can you manage it at home?
The following steps can help you manage your condition:
- Get regular medical care. You may need follow-up visits to your doctor to see whether your treatment is working. Tell your doctor if your symptoms get worse or if you get new symptoms. You may also need treatment for pain, extreme tiredness, and depression.
- Get regular physical activity. Physical activity can help you breathe easier. Before starting any exercise program, ask your doctor about what level of physical activity is right for you.
- Get routine vaccines. You may need routine pneumococcal, flu (influenza), and COVID-19 vaccines to avoid lung infections that can make your condition worse.
- Quit smoking. If you smoke, quit. Smoking can make your lung damage worse.