Causes Make an Appointment Refer a Patient Ask a Question Reviewed by Cecile S. Rose, MD, MPH (June 01, 2012) 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. Symptoms Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.