Propylene glycol, known also by the systematic name propane-1,2-diol, is an organic compound (a diol alcohol), usually a faintly sweet, odorless, and colorless clear viscous liquid that is hygroscopic and miscible with water, acetone, and chloroform.
It is the main ingredient in the majority of E-Liquid on the market. When it is heated, it becomes a thick vapour that resembles cigarette smoke.
Cases of propylene glycol poisoning are related to either inappropriate intravenous use or accidental ingestion by children.<ref>National Library of Medicine;. Human Toxicity Excerpts: CAS Registry Number: 57-55-6 (1,2-Propylene Glycol). Selected toxicity information from HSDB. 2005. </ref> The oral toxicity of propylene glycol is very low. In one study, rats were provided with feed containing as much as 5% PG over a period of 104 weeks and they showed no apparent ill effects.<ref>Gaunt, IF, Carpanini, FMB, Grasso, P and Lansdown, ABG, Long-term toxicity of propylene glycol in rats, Food and Cosmetics Toxicology, Apr. 1972, 10(2), pages 151 - 162. </ref> Because of its low chronic oral toxicity, propylene glycol is generally recognized as safe (GRAS) for use as a direct food additive.
Serious toxicity will occur only at extremely high intakes over a relatively short period of time that result in plasma concentrations of over 4 g/L.<ref>Flanagan RJ;Braithwaite RA;Brown SS;Widdop B;de Wolff FA;. The International Programme on Chemical Safety: Basic Analytical Toxicology. WHO, 1995.</ref> Such levels of ingestion would not be possible when consuming reasonable amounts of a food product or dietary supplements containing at most 1 g/kg propylene glycol.
The U.S. Food and Drug Administration (FDA) has determined propylene glycol to be "generally recognized as safe" for use in food, cosmetics, and medicines. Like ethylene glycol, propylene glycol affects the body's chemistry by increasing the amount of acid. Propylene glycol is metabolized into pyruvic acid, which is a normal metabolite in the breakdown of glucose, while ethylene glycol is metabolized into oxalic acid, which is toxic.
However, propylene glycol is not approved for use in cat food. The U.S. Food and Drug Administration has determined that propylene glycol in or on cat food has not been shown by adequate scientific data to be safe for use. Use of propylene glycol in or on cat food causes the feed to be adulterated and in violation of the Federal Food, Drug, and Cosmetic Act. 21CFR589.1001
Prolonged contact with propylene glycol is essentially non-irritating to the skin. Undiluted propylene glycol is minimally irritating to the eye, and can produce slight transient conjunctivitis (the eye recovers after the exposure is removed). Exposure to mists may cause eye irritation, as well as upper respiratory tract irritation. Inhalation of the propylene glycol vapors appears to present no significant hazard in ordinary applications. However, limited human experience indicates that inhalation of propylene glycol mists could be irritating to some individuals. Therefore inhalation exposure to mists of these materials should be avoided. Some research has suggested that propylene glycol not be used in applications where inhalation exposure or human eye contact with the spray mists of these materials is likely, such as fogs for theatrical productions or antifreeze solutions for emergency eye wash stations.<ref>A Guide to Glycols (http://www.dow.com/PublishedLiterature/dh_02aa/09002f13802aaf25.pdf), page 36.</ref>
Propylene glycol does not cause sensitization and it shows no evidence of being a carcinogen or of being genotoxic.<ref>1,2-Dihydroxypropane SIDS Initial Assessment Profile (http://www.chem.unep.ch/irptc/sids/OECDSIDS/57-55-6.pdf), UNEP Publications, SIAM 11, U.S.A, January 23-26, 2001, page 21.</ref><ref>Title 21, U.S. Code of Federal Regulations. 1999. </ref>
A Clinical Journal of Medicine article states two cases of adult men experiencing psychosis from use of propylene glycol used in phenytoin injection USP. Both patients had to be switched to Cerebyx (Fosphenytoin Sodium) in order to avoid propylene glycol co-solvent.Template:Fact
Research has suggested that individuals who cannot tolerate propylene glycol probably experience a special form of irritation, but that they only rarely develop allergic contact dermatitis. Other investigators believe that the incidence of allergic contact dermatitis to propylene glycol may be greater than 2% in patients with eczema.<ref>[American Medical Association, Council on Drugs. AMA Drug Evaluations Annual 1994. Chicago, IL: American Medical Association, 1994., p. 1224]</ref>
Patients with vulvodynia and interstitial cystitis may be especially sensitive to propylene glycol. Women struggling with yeast infections may also notice that some OTC creams can cause intense burning.<ref>Elizabeth Vliet MD, Screaming To Be Heard: Hormonal Connections That Women Suspect and Doctors Ignore". M. Evans and Company, Inc. New York 1995</ref>Post menopausal women who require the use of an oestrogen cream may notice that brand name creams made with propylene glycol often create extreme, uncomfortable burning along the vulva and perianal area. In these cases, patients can request that a local compounding pharmacy make a "propylene glycol free" cream.
Propylene glycol is used:
- As a moisturizer in medicines, cosmetics, food, toothpaste, mouth wash, and tobacco products
- In electronic cigarettes to deliver vaporized nicotine.
- As a medical and sexual lubricant (A.K.A. "personal lubricant")
- As an emulsification agent in Angostura and orange bitters
- As a solvent for food colors and flavorings
- As a humectant food additive, labeled as E number E1520
- As a cooling agent for beer and wine glycol jacketed fermentation tanks
- As a carrier in fragrance oils
- As a less toxic antifreeze
- As a solvent used in mixing photographic chemicals, such as film developers
- In smoke machines to make artificial smoke for use in firefighters' training and theatrical productions
- In hand sanitizers, antibacterial lotions, and saline solutions
- In cryonics
- As a working fluid in hydraulic presses
- As a coolant in liquid cooling systems
- To regulate humidity in a cigar humidor
- As the killing and preserving agent in pitfall traps, usually used to capture ground beetles
- To treat livestock ketosis
- As the main ingredient in deodorant sticks.
- To de-ice aircraft.
- UV Blacklite Tattoo Ink
Propylene glycol has properties similar to those of ethylene glycol (monoethylene glycol, or MEG). (Note: propylene glycol may also use the acronym MEG, but as an abbreviation of methyl ethyl glycol.) The industrial norm is to replace ethylene glycol by propylene glycol.