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What is Hypersensitivity Pneumonitis?

Hypersensitivity PneumonitisHypersensitivity 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.[1]


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.[2]

There are a wide variety of substances that can be inhaled as a fine dust and cause hypersensitivity pneumonitis.2 These include:1

  • Bacteria and mycobacteria (a type of germ, the most common causing tuberculosis and leprosy)
  • Fungi or molds
  • Proteins
  • Chemicals

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

  • Dry cough
  • Shortness of breath
  • Chest tightness
  • Fever and chills
  • Tiredness

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

  • Oxygen therapy for those with low blood oxygen levels.
  • Bronchodilators to help relax and widen the airways making it easier to breathe.
  • Opioid medications to help relieve shortness of breath and chronic (ongoing) cough that is resistant to standard treatment. It’s important to note that continuous use of opioid narcotics may result in physical dependence and addiction.

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.

How to Limit Your Exposure to Dust

Successful management of hypersensitivity pneumonitis involves limiting your exposure to certain dusts. If you’re unsure where to start, check out the following tips:

  • Get rid of still or stagnant water – this includes inside and outside your home. Why? It can be a breeding ground for allergy-causing bacteria and fungi.
  • Maintain the humidity in your home or work – aim at keeping it below 60%.
  • Repair water damage ASAP – this includes removing any water-damaged carpet, furniture and dry-wall inside your home or work.
  • Perform routine maintenance on your heating, air conditioning and ventilation systems.
  • Avoid re-circulating water in your heating, air conditioning and ventilation systems.
  • Properly dry and store farm products – if you work with them.
  • Consider an air-purifying respirator – if you cannot completely avoid dust exposure.

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.

[1] National Heart, Lung and Blood Institute. Hypersensitivity Pneumonitis. Accessed December 23, 2017

[2] American Lung Association. Hypersensitivity Pneumonitis. Accessed December 23, 2017.


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