Pneumonia is believed to be caused by microscopic entities.
 Some parasites, in particular those belonging to the Ascaris and Strongyloides genera, stimulate a strong eosinophilic reaction, which may result in eosinophilic pneumonia
Factors that predispose to pneumonia include smoking, immunodeficiency, alcoholism, chronic obstructive pulmonary disease, sickle cell disease (SCD), asthma, chronic kidney disease, liver disease, and biological aging

