Reviewed by Cecile S. Rose, MD, MPH
Hypersensitivity pneumonitis (HP) is an inflammation of the lungs caused by inhaling a foreign substance.
These foreign substances can stimulate an immune reaction in the small airways and air sacs of the lung. This may lead to acute lung disease. Over time and with continued exposure to the causative substance, long-lasting (chronic) lung disease with permanent scarring can occur.