Glycerin (glycerol; propanetriol) — a humectant used in moisturizers. It is water-binding and able to draw and absorb water from the air, thus helping the skin retain moisture. Glycerin has been studied extensively for its hydrating abilities. Based on the data available, glycerin has been established as a good skin-moisturizing agent. At least part of its activity is attributed to its facilitating enzymatic reactions in the skin, thereby promoting corneocyte desquamation. Glycerin also improves the spreading qualities of creams and lotions. It is a clear, syrupy liquid made by chemically combining water and fat that is usually derived from vegetable oil. Although glycerin has not been shown to cause allergies, it may be comedogenic and irritating to the mucous membranes when used in concentrated solutions.