Hypersensitivity Pneumonitis Symptoms, Causes and Risk Factors | American Lung Association

Hypersensitivity Pneumonitis Symptoms, Causes and Risk Factors

A variety of materials that are inhaled as a fine dust can cause hypersensitivity pneumonitis. It can take several months to a number of years to develop allergy to the dust. Only a small number of people who inhale this dust actually develop hypersensitivity pneumonitis.

What Are the Symptoms of Hypersensitivity Pneumonitis?

You may feel like you have caught the flu when the acute attack occurs. It appears about 4 to 6 hours after you inhale the dust. The symptoms seen are:

The initial symptoms may last for as little as 12 hours but may continue for several days in some individuals. If you have repeated exposure to the dust, the following symptoms may be seen.

  • Shortness of breath, especially with activity
  • Dry cough
  • Unintentional weight loss

What Causes Hypersensitivity Pneumonitis?

There are more than 300 known substances which, when inhaled as a fine dust, have been known to cause hypersensitivity pneumonitis. Some commonly seen problems are given specific names related to the source of the dust, including

Farmer's lung: seen in farmers and cattle workers, this condition is caused by breathing mold that grows on hay, straw and grain.
Bird fancier's lung: (also called pigeon breeder's disease) caused by breathing particles from feathers or droppings of many species of birds.
Humidifier lung: can develop by breathing in fungus growing in humidifiers, air conditioners and heating systems, particularly if they are not well maintained.
Hot tub lung: may develop by breathing in bacteria that may be found in the water vapor coming from indoor hot tubs.

What Are Risk Factors?

If you work in certain occupations, then you may be at an increased risk of developing hypersensitivity pneumonitis. This includes farmers, vegetable or dairy cattle workers, bird and poultry handlers, veterinary workers and animal handlers, grain and flour processing and loaders, lumber milling, wood stripping and paper and wallboard manufacturers. Another risk factor is inhaling certain chemicals produced in plastic manufacturing, painting, and the electronics industry.

Most individuals who work in such occupations do not develop hypersensitivity pneumonitis. It appears that certain genetic factors determine if you are going to develop hypersensitivity pneumonitis or not. Unfortunately, at this time, there is not much information about the genes that can predispose a person to develop hypersensitivity pneumonitis.

When to See Your Doctor

If you develop symptoms of hypersensitivity pneumonitis, contact your doctor. You may feel like you have caught the flu when the acute attack occurs. You may notice a dry cough, shortness of breath, chest tightness, fever, chills, or tiredness about 4 to 6 hours after you inhale the dust. Unlike the common flu, which most commonly occurs during October to May, hypersensitivity pneumonitis symptoms can occur during any time of the year. You may notice dry cough or shortness of breath on activity if you have repeated exposure to the dust.  Your coworkers or family members may not have any symptoms but your lungs could still be allergic to some dust at workplace or home respectively.


    This content was developed in partnership with the CHEST Foundation, the philanthropic arm of the American College of Chest Physicians.


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