What is hypersensitivity pneumonitis?

Hypersensitivity pneumonitis (HP) is a lung disease causing inflammation (swelling and sensitivity) of the lung tissue. This inflammation makes breathing difficult. It can lead to irreversible lung scarring over time.

HP results from breathing in specific environmental allergens. Allergens are substances that cause an allergic reaction in the body. These allergens may be present at home, at work, or in nature. Bird feathers and droppings, and household mold are examples of common allergens.

Who is likely to have hypersensitivity pneumonitis?

People working in certain occupations are more likely to develop HP. These occupations include:

  • Farmers, including those working with dairy cattle or vegetables
  • Animal handlers, including veterinarians and bird or poultry handlers
  • People who process and load grains or flour
  • Individuals working in lumber mills or who strip wood
  • Wallboard and paper manufacturers
  • Certain individuals in the electronics, plastic manufacturing, and painting industries

Other activities that expose you to allergens can increase your likelihood of developing HP. These include:

  • Keeping pet birds and breathing allergens from bird droppings or feathers (known as bird fancier’s lung)
  • Breathing allergens from humidifiers, heating systems, or air conditioners, especially if they are not cleaned properly or well-maintained (humidifier lung)
  • Inhaling bacteria found in hot tub water vapor (hot tub lung)

Is hypersensitivity pneumonitis contagious?

HP is not contagious.

What causes hypersensitivity pneumonitis?

HP results from inhaling certain allergens into the lungs. Over 300 substances are known to cause HP, including:

  • Bacteria
  • Molds and fungi
  • Some chemicals
  • Certain proteins

These substances cause inflammation of the lung tissue when inhaled. In many cases, the lungs remain inflamed over time, with repeated exposure to an allergen.

Many cases of HP occur acutely (suddenly). In general, acute (or sudden) HP symptoms occur 4- 6 hours after allergens are inhaled. These cases usually are treated successfully.

Some people develop chronic hypersensitivity pneumonitis. You are more likely to develop chronic hypersensitivity pneumonitis if you are exposed to low levels of allergens constantly over an extended period. The symptoms of chronic HP develop over months or years.

What are the symptoms of hypersensitivity pneumonitis?

The symptoms of HP depend on whether the disease is acute or chronic. In general, symptoms of acute, or sudden, HP last between 12 hours and several days. Symptoms of acute HP may include:

  • Shortness of breath
  • Dry cough
  • Chest tightness
  • Chills
  • Fatigue
  • Fever

The symptoms of chronic HP may include:

  • Shortness of breath, especially with exertion or activity
  • Cough
  • Fatigue
  • Weight loss

In rare cases, chronic HP leads to irreversible, permanent scarring of the lung tissue. This condition is called pulmonary fibrosis. This serious disease causes symptoms resulting from too little oxygen reaching body tissues.

Pulmonary fibrosis symptoms may include:

  • Shortness of breath
  • Fast, shallow breathing
  • Dry, hacking cough
  • Weight loss
  • Fatigue
  • Finger and toe clubbing (rounding and widening)

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