Encylopedia Article 1)
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound (a diol or double alcohol) with formula C3H8O2. It is a colorless, nearly odorless, clear, viscous liquid with a faintly sweet taste, hygroscopic and miscible with water, acetone, and chloroform.
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Propylene glycol is considered generally recognized as safe (GRAS) by the U.S. Food and Drug Administration, and it is used as an humectant (E1520), solvent, and preservative in food and for tobacco products, as well as being one of the major ingredients of the “e-liquid” used in electronic cigarettes along with vegetable glycerin. Vaporizers used for delivery of pharmaceuticals or personal care products often include propylene glycol among the ingredients they are filled with. Propylene glycol is used as a solvent in many pharmaceuticals, including oral, injectable and topical formulations, such as for diazepam and lorazepam which are insoluble in water.
 Carl J. Sullivan (2005), “Propanediols”, Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a22_163
 Janusz Szajewski, MD , Warsaw Poison Control Centre (August 1991). “Propylene glycol (PIM 443)”. IPCS INChem. Retrieved July 2, 2009.