|High magnification photomicrograph of a lung biopsy taken showing chronic hypersensitivity pneumonitis (H&E), showing mild expansion of the alveolar septa (interstitium) by lymphocytes.[clarification needed] A multinucleated giant cell, seen within the interstitium to the right of the picture halfway down, is an important clue to the correct diagnosis.|
|Classification and external resources|
Hypersensitivity pneumonitis (HP; also called allergic alveolitis or extrinsic allergic alveolitis, EAA) is an inflammation of the alveoli within the lung caused by hypersensitivity to inhaled organic dusts. Sufferers are commonly exposed to the dust by their occupation or hobbies.