Lipoid pneumonia can be subdivided into exogenous and endogenous lipoid pneumonia, depending on the origin of the lipid products associated with this lesion.

Exogenous lipoid pneumonia is produced by inhalation of mineral oil or a similar product. It usually occurs due to chronic inhalation of small quantities of these products, which reach the distal lung. Most cases are seen in individuals who use mineral oil as a laxative, use oily nose drops, or are exposed to industrial inhalation of oily substances or conditions predisposing to chronic aspiration. Over time, fibrosis develops in the areas of pneumonia. Differential diagnosis includes nontuberculous mycobacterial infection (special stains for mycobacteria should always be obtained).

Endogenous lipoid pneumonia is much more common than exogenous lipoid pneumonia. It is also known as postobstructive pneumonia or golden pneumonia (because of the yellow color produced by the lipids). It is characterized by accumulation of foamy macrophages in the alveolar spaces and interstitium. Their cytoplasm is finely vacuolated (in contrast to the large vacuoles seen in exogenous lipoid pneumonia). Endogenous lipoid pneumonia is frequently seen distal to areas of obstruction (due to malignancy, inflammation, foreign bodies, etc.) where there is accumulation of endogenous lipids and cholesterol from cellular debris and blood due to the obstruction.