Propylene glycol (C3H8O2) is an almost odorless clear, colorless, syrupy synthetic liquid with a slightly sweet taste. It is used to absorb water. Propylene glycol has many industrial uses and is classified as a food additive generally recognized as safe by the Food and Drug Administration.
As an food additive, propylene glycol is a solvent for flavor and color and is used to absorb excess water and maintain moisture in foods, pharmaceuticals and cosmetics. It is the primary ingredient in the liquid used in e-cigarettes along with vegetable glycerin. Because it lowers the freezing point of water, it serves as antifreeze in environments where a leak could cause it to come into contact with food that would be toxic if other common antifreeze agents were used. Propylene glycol is also frequently used in the production of polyester compounds and as a base for de-icing solutions. It is a solvent in paints and plastics. In theater productions and firefighter training, it is used to create artificial fog or smoke. Frequent skin exposure to propylene glycol can lead to skin irritation. When it breaks down on the surface of water, it creates high levels of biochemical oxygen demand; its decomposition consumes large amounts of oxygen that can be harmful for aquatic life.