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Hypersensitivity pneumonitis, also known as extrinsic allergic alveolitis or allergic alveolitis, is a rare immune system disorder of the lungs caused by exposure to dust and other substances found in the environment. These substances trigger an immune response in the lungs that causes short or long-term inflammation, primarily in a part of the lungs called the interstitium. This inflammation results in the lungs not functioning properly and, if the disease isn’t detected early enough and the exposure continues, irreversible lung damage.
Hypersensitivity pneumonitis is caused by an allergic reaction to certain environmental substances that cause inflammation in the lungs when inhaled. This inflammation can be reversed, if the disease is detected in its early stages and you avoid the allergen (allergy-producing substance). If it goes undetected and exposure to the allergen continues, irreversible pulmonary fibrosis (lung scarring) may occur for which there is no effective cure or treatment.
There are a wide variety of substances that can be inhaled as a fine dust and cause hypersensitivity pneumonitis.2 These include:1
It takes repeated exposure to these substances over a period of several months to a number of years to develop an allergic response to them. Only a small percentage of people who inhale the dust will go on to develop hypersensitivity pneumonitis.2
The following symptoms may occur 4 to 6 hours after your initial exposure to the dust:2
If no further exposure to the allergen occurs, initial symptoms usually resolve after a few days. If exposure continues, symptoms may worsen and include shortness of breath, especially with activity, dry cough, unintentional weight loss, fatigue, lung fibrosis, chronic bronchitis and clubbing of the fingers (a condition in which the tips of the fingers enlarge and the nails curve around the fingertips).1
The single most important treatment option for people with hypersensitivity pneumonitis is to avoid further exposure to the allergen that initially caused the disease. If you avoid repeated exposure to the dust in the early stages of the disease, your lung function can return to normal.1
If avoidance strategies are unsuccessful, the following supportive treatments may help relieve symptoms:1
If avoidance strategies and medication are unsuccessful in the management of your symptoms and you develop serious complications, a lung transplant may be a viable option. To find out if you qualify, contact your primary care provider or lung specialist.
Successful management of hypersensitivity pneumonitis involves limiting your exposure to certain dusts. If you’re unsure where to start, check out the following tips:
For more information about hypersensitivity pneumonitis, talk to your primary care provider or lung specialist. To find a support group, join the Living with Lung Disease Support Community, brought to you by the American Lung Association.
 National Heart, Lung and Blood Institute. Hypersensitivity Pneumonitis. Accessed December 23, 2017
 American Lung Association. Hypersensitivity Pneumonitis. Accessed December 23, 2017.