Carminic acid is the active colouring agent in both carmine and the less pure cochineal. It is rarely used in practice, however, since the considerably more easily obtained carmine is as effective in biological staining. Carmine is a valuable dye, which is invariably applied in conjunction with a mordant, usually aluminum. It can be used to stain glycogen (Best's carmine), acid mucopolysaccharides (mucicarmine), and nuclei (carmalum). Carmine is obtained from the bodies of the female of the insect Coccus cacti.

Compare this dye with other dyes obtained from the bodies of insects, Kermes and Lac.