What are the causes of hypersensitivity pneumonitis?

Hypersensitivity pneumonitis (HP) is a lung disease caused by an allergic reaction to inhaled antigens. These antigens can be found in a variety of substances, including mold, bacteria, fungi, and animal proteins.

The most common cause of HP is exposure to mold spores, which can be found in damp or moldy environments such as homes, offices, and farms. Other common causes include exposure to bacteria or fungi found in compost, hay, or animal dander.

Less common causes of HP include exposure to certain chemicals, such as isocyanates, which are found in some paints and plastics.

In some cases, HP can also be caused by an allergic reaction to inhaled medications, such as antibiotics or chemotherapy drugs.