Pneumonitis occurs when some irritating substance causes the tiny air sacs (alveoli) in your lungs to become inflamed. This inflammation can interfere with the delivery of oxygen to your bloodstream.

A variety of irritants, ranging from airborne molds to chemotherapy drugs, have been linked to pneumonitis. But for most people, the specific substance causing the inflammation is never identified. Pneumonitis causes may include:

  • Drugs. A variety of drugs used to treat other conditions can cause pneumonitis, including some antibiotics, several types of chemotherapy drugs and medications that keep your heartbeat regular. An overdose of aspirin can cause pneumonitis.
  • Molds. Specific varieties of mold-related pneumonitis have received nicknames, such as "farmer's lung" or "hot tub lung."
  • Birds. Exposure to feathers or bird excrement is a common cause of pneumonitis.
  • Radiation treatments. Some people who undergo radiation therapy to the chest, such as for breast or lung cancer, may develop pneumonitis. Pneumonitis also can occur after whole-body radiation therapy, which is needed to prepare a person for a bone marrow transplant.
Jun. 03, 2011