Glycerol is a chemical compound also commonly called glycerin or glycerine. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. For human consumption, glycerol is classified by the FDA among the sugar alcohols as a caloric macronutrient. Glycerol has three hydrophilic hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. Its surface tension is 64.00 mN/m at 20 °C , and it has a temperature coefficient of -0.0598 mN/(m K). The glycerol substructure is a central component of many lipids. Glycerol is sweet-tasting and of low toxicity.