Hypersensitivity pneumonitis (HP) or extrinsic allergic alveolitis (EAA) is a rare immune system disorder that affects the lungs. It is an inflammation of the airspaces (alveoli) and small airways (bronchioles) within the lung, caused by hypersensitivity to inhaled organic dusts and molds. People affected by this type of lung inflammation (pneumonitis) are commonly exposed to the dust and mold by their occupation or hobbies.
In humans, breathing feather dander is the cause of allergic alveoliitis in people sensitive to bird protein. Any bird can transmit this disease; however, cockatoos, cockatiels and amazons that produce more "powder" than other birds are liable to be more potentially irritating to humans.