The oil red o stain is used to demonstrate the presence of fat in fatty liver disease specimens. The oil red o stain is the oldest and most common stain for the demonstration of lipid/fat. The staining mechanism of the oil red o stain is a physical process rather than chemical.
The oil red o stain must be performed on "fresh" frozen sections fixed in formalin as lipid/fat is removed during tissue processing. Additionally, air bubbles resulting from coverslipping should not be pressed out, as stained lipid/fat will be displaced.
