Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis, also known as extrinsic allergic alveolitis, is a syndrome caused by the repetitive inhalation of antigens from the environment in susceptible or sensitized people. Common antigens include molds, bacteria, bird droppings, bird feathers, agricultural dusts, bioaerosols, and chemicals from paints or plastics, and people affected are commonly exposed to the antigens through their occupations, hobbies, environment, or animals. The inhaled antigens produce a hypersensitivity immune reaction causing inflammation of the airspaces and small airways within the lung, and hypersensitivity pneumonitis may eventually lead to interstitial lung disease.