Linoleic acid. Interference light micrograph of liquid crystals of the essential fatty acid linoleic acid (cis, cis- 9, 12-octadecadienoic acid) in aqueous ammonia solution. Linoleic acid (lower frame) is comprised of carbon (C), hydrogen (H) and oxygen (O), is an unsaturated fat and has the chemical formula C18H32O2. Linoleic acid occurs widely in vegetable oils and animal fats. Cholesteryl linoleate is an important constituent of blood. Linoleic acid is one of the most important essential fatty acids and is required for good health. As the human body cannot make linoleic acid it must be obtained from food. Magnification: x25 at 35mm size.