When you breathe, air travels through your nose, down the trachea, and into smaller airways called bronchi. The bronchi branch into even smaller passages called bronchioles, and finally into tiny, thin, fragile grape-like sacs called alveoli. In the alveoli, oxygen is exchanged for carbon dioxide in the blood.
Pneumonitis is one of a group of diseases classified as "interstitial lung diseases." These are diseases that cause chronic inflammation and scarring of the alveoli (air sacs) and their supporting structures (the interstitium). This scarring prevents the alveoli from properly transferring oxygen to the bloodstream. In some cases, fluid accumulates in the lung space, further complicating respiration.
There are several causes for pneumonitis, including exposure to allergens, radiation, and certain types of chemicals. Symptoms of pneumonitis include shortness of breath and cough. Treatment depends on the underlying cause of the pneumonitis; however oxygen and corticosteroids may be given to reduce inflammation.