HP typically is found in people who work in places where there are high levels of organic dusts.
The most common type of this disease is “bird fancier’s lung.” This is caused by repeated or intense exposure to proteins found in the feathers or droppings of many species of birds.
The disease can also be caused by exposure to:
dust from moldy hay, straw, and grain
aerosols containing fungi
bacteria in humidifiers, heating systems and air conditioners
certain chemicals, such as isocyanates, as well as use of some medications can also lead to HP.