Pneumonitis describes general inflammation of lung tissue. Possible causative agents include radiation therapy of the chest, exposure to medications used during chemo-therapy, the inhalation of debris (e.g., animal dander), aspiration, herbicides or fluorocarbons and some systemic diseases. If unresolved, continued inflammation can result in irreparable damage such as pulmonary fibrosis. Pneumonitis is distinguished from pneumonia on the basis of causation as well as its manifestation. Pneumonia can be described as pneumonitis combined with consolidation and exudation of lung tissue due to infection with microorganisms. The distinction between Pneumonia and Pneumonitis can be further understood with Pneumonitis being the encapsulation of all respiratory infections (incorporating pneumonia and pulmonary fibrosis as major diseases), and pneumonia as a localized infection. For most infections, the immune response of the body is enough to control and apprehend the infection within a couple days, but if the tissue and the cells can't fight off the infection, the creation of pus will begin to form in the lungs which then hardens into lung abscess or suppurative pneumonitis. Patients that are immunodeficient and don't get treated immediately for any type of respiratory infection may lead to more severe infections and/or death. Pneumonitis can be classified into several different specific subcategories, including hypersensitivity pneumonitis, radiation pneumonitis, acute interstitial pneumonitis, and chemical pneumonitis. These all share similar symptoms, but differ in causative agents. Diagnosis of pneumonitis remains challenging, but several different treatment paths (corticosteroids, oxygen therapy, avoidance) have seen success. Causes Alveoli are the primary structure affected by pneumonitis. Any particles that are smaller than 5 microns can enter the alveoli of the lungs. These tiny air sacs facilitate the passage of oxygen from inhaled air to the bloodstream. In the case of pneumonitis, it is more difficult for this exchange of oxygen to occur since irritants have caused inflammation of the alveoli. Due to the lack of a definitive determination of a single irritant causing pneumonitis, there are several possible causes. Viral infection. Measles can cause severe pneumonitis, and ribavirin has been proposed as a possible treatment. CMV is another cause. Pneumonia Radiation therapy Inhaling chemicals, such as sodium hydroxide Interstitial lung disease Sepsis Adverse reaction to medications Hypersensitivity to inhaled agents Inhalation of spores of some species of mushroom (bronchoalveolar allergic syndrome) Mercury exposure Smoking Overexposure to chlorine Bronchial obstruction (obstructive pneumonitis or post-obstructive pneumonitis) Ascariasis (during parasite migration) Aspirin overdose, some antibiotics, and chemotherapy drugs “Farmer’s lung”