Also known as extrinsic allergic alveolitis, bird fancier’s lung, farmer’s lung, hot tub lung, and humidifier lung.
Hypersensitivity pneumonitis is a rare immune system disorder that affects the lungs. It occurs in some people after they breathe in certain substances they encounter in the environment. These substances trigger their immune systems, causing short- or long-term inflammation, especially in a part of the lungs called the interstitium. This inflammation makes it harder for the lungs to function properly and may even permanently damage the lungs. If diagnosed, some types of hypersensitivity pneumonitis are treatable by avoiding exposure to the environmental substances or with medicines such as corticosteroids that reduce inflammation. If the condition goes untreated or is not well controlled over time, the chronic inflammation can cause irreversible scarring of the lungs that may severely impair their ability to function.
Explore the hypersensitivity pneumonitis Health Topic sections to learn more about this condition, NHLBI’s role in research and clinical trials to improve health, and where to find more information.