Common causes of pneumonitis include handling birds, medication, mold, bacteria and radiation treatment, according to Mayo Clinic. For many cases, however, the cause is never discovered. Pneumonitis is a lung inflammation caused by an irritant.
Frequent irritants that causes pneumonitis are bird droppings or feathers, Mayo Clinic reports. Molds and bacteria, after repeated exposure, can also cause the inflammation. Some specific molds and bacteria that cause pneumonitis have nicknames, such as "hot tub lung."
Medication is another common cause of pneumonitis, Mayo Clinic says. Antibiotics, chemotherapy drugs and even an aspirin overdose can cause lung inflammation. Radiation treatments, especially those targeted at the chest, can cause the condition. Full-body radiation to prepare patients for bone marrow transplants is also a culprit.
Risk factors for pneumonitis include professions such as farming, pigeon breeders and poultry handlers, Mayo Clinic reports. Farmers are exposed to chemicals that can irritate lungs as well as mold found in hay and grains. Poultry handlers and pigeon breeders are exposed to feathers and excrement that can cause inflammation.
Bubbling, warm water from humidifiers and hot tubs in the home can also put people at risk for pneumonitis, Mayo Clinic says. The bubbly water creates a fine mist that is easily inhaled, which makes it easy for molds that cause pneumonitis to get into the lungs.