Propylene glycol

Propylene glycol
Propylene glycol[1]
CAS number 57-55-6 YesY
PubChem 1030
ChemSpider 1003 YesY
UNII 6DC9Q167V3 YesY
RTECS number TY6300000
ATCvet code QA16QA01
Jmol-3D images Image 1
Molecular formula C3H8O2
Molar mass 76.09 g/mol
Density 1.036 g/cm³
Melting point

−59 °C (−74 °F)

Boiling point

188.2 °C (370.8 °F)

Solubility in water fully miscible
Solubility in ethanol fully miscible
Solubility in diethyl ether fully miscible
Solubility in acetone fully miscible
Solubility in chloroform fully miscible
Thermal conductivity 0.34 W/m-K (50% H2O @ 90 °C (194 °F))
MSDS External MSDS
S-phrases S24 S25
NFPA 704
NFPA 704.svg
Related compounds
Related glycols Ethylene glycol 1,3-propanediol
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound (a diol or double alcohol) with formula C3H8O2 or HO-CH2-CHOH-CH3. It is a colorless, nearly odorless, clear, viscous liquid with a faintly sweet taste, hygroscopic and miscible with water, acetone, and chloroform.

The compound is sometimes called α-propylene glycol to distinguish it from the isomer propane-1,3-diol HO-(CH2)3-OH, also called β-propylene glycol.



Propylene glycol contains an asymmetrical carbon atom, so it exists in two stereoisomers. The commercial product is a racemic mixture. Pure optical isomers can be obtained by hydration of optically pure propylene oxide.[2]


Industrially, propylene glycol is produced from propylene oxide.[3] Different manufacturers use either non-catalytic high-temperature process at 200 °C (392 °F) to 220 °C (428 °F), or a catalytic method, which proceeds at 150 °C (302 °F) to 180 °C (356 °F) in the presence of ion exchange resin or a small amount of sulfuric acid or alkali.

Final products contain 20% 1,2-propanediol, 1.5% of dipropylene glycol and small amounts of other polypropylene glycols.[4] Further purification produces finished industrial grade or USP/JP/EP/BP grade propylene glycol that is typically 99.5% or greater. Propylene glycol can also be converted from glycerol, a biodiesel byproduct.


Propylene glycol is used:

  • As an ingredient in the oil dispersant Corexit, used in great quantities during the Deepwater Horizon oil spill.[5][6]
  • As a solvent in many pharmaceuticals, including oral, injectable and topical formulations. Notably, diazepam, which is insoluble in water, uses propylene glycol as its solvent in its clinical, injectable form.[7]
  • As a humectant food additive, labeled as E number E1520
  • As an emulsification agent in Angostura and orange bitters
  • As a moisturizer in medicines, cosmetics, food, toothpaste, shampoo, mouth wash, hair care and tobacco products
  • As a carrier in fragrance oil
  • To produce polyester compounds
  • As a base in deicing solution
  • As an ingredient in massage oils
  • In hand sanitizers, antibacterial lotions, and saline solutions
  • In smoke machines to make artificial smoke for use in firefighters' training and theatrical productions
  • In electronic cigarettes, as a vaporizable base for diluting the nicotine liquid
  • As a solvent for food colors and flavorings
  • As an ingredient, along with wax and gelatin, in the production of paintballs
  • As a moisture stabilizer (humectant) for snus (Swedish style snuff).
  • As a cooling agent for beer and wine glycol jacketed fermentation tanks
  • As a non-toxic antifreeze for winterizing drinking water systems, and in applications where the used antifreeze eventually will be drained into the soil, water, or a septic system.[8]
  • As a less-toxic antifreeze in solar water heating systems
  • As a solvent used in mixing photographic chemicals, such as film developers
  • 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
  • As an additive to pipe tobacco to prevent dehydration.
  • To treat livestock ketosis
  • As the main ingredient in deodorant sticks.
  • To de-ice aircraft.[9]
  • As an ingredient in UV or blacklight tattoo ink
  • As a lubricant in air conditioning compressors.
  • As a wetting agent, used to determine drying time in paints and coatings

Propylene glycol has properties similar to those of highly toxic ethylene glycol (monoethylene glycol, or MEG). (Note: Infrequently propylene glycol may also use the acronym MEG, but as an abbreviation of methyl ethyl glycol- the industry standard acronym for propylene glycol is PG or MPG (monopropylene glycol)). The industrial norm is to replace ethylene glycol with propylene glycol when safer properties are desired.


Propylene glycol is a component in newer automotive antifreezes and de-icers used at airports. Like ethylene glycol, the freezing point of propylene glycol is depressed when mixed with water due to disruption of hydrogen bonding. Unlike ethylene glycol, propylene glycol is of very low toxicity. Both are readily biodegradable.

Freezing Points of Propylene Glycol – Water Mixtures[10]
Percent Propylene Glycol (wt. %) Freezing Point (°F) Freezing Point (°C)
0 32 0
10 26 -3
20 20 -7
30 10 -12
36 0 -18
40 -5 -20
43 -10 -23
48 -20 -29
52 -30 -34
55 -40 -40
58 -50 -46
60 -60 -51



The acute oral toxicity of propylene glycol is very low, and large quantities are required to cause perceptible health damage in humans; propylene glycol is metabolized in the human body into pyruvic acid (a normal part of the glucose-metabolism process, readily converted to energy), acetic acid (handled by ethanol-metabolism), lactic acid (a normal acid generally abundant during digestion),[11] and propionaldehyde (a highly toxic substance)[12].[13][14] Serious toxicity generally occurs only at plasma concentrations over 1 g/L, which requires extremely high intake over a relatively short period of time.[15] It would be nearly impossible to reach toxic levels by consuming foods or supplements, which contain at most 1 g/kg of PG. Cases of propylene glycol poisoning are usually related to either inappropriate intravenous administration or accidental ingestion of large quantities by children.[16] The potential for long-term oral toxicity is also low. In one study, rats were provided with feed containing as much as 5% PG in feed over a period of 104 weeks and they showed no apparent ill effects.[17] Because of its low chronic oral toxicity, propylene glycol was classified by the U. S. Food and Drug Administration as "generally recognized as safe" (GRAS) for use as a direct food additive.

Prolonged contact with propylene glycol is essentially non-irritating to the skin.[18] 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.[19] 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.[20]

Propylene glycol does not cause sensitization and it shows no evidence of being a carcinogen or of being genotoxic.[21][22]

Adverse responses to intravenous administration of drugs which use PG as an excipient have been seen in a number of people, particularly with large dosages thereof. Responses may include "hypotension[,] bradycardia... QRS and T abnormalities on the ECG[,] arrhythmia[,] cardiac arrest[,] serum hyperosmolality[,] lactic acidosis[,] and haemolysis".[23] A high percentage (12% to 42%) of directly-injected propylene glycol is eliminated/secreted in urine unaltered depending on dosage, with the remainder appearing in its glucuronide-form. The speed of renal filtration decreases as dosage increases,[24] which may be due to propylene glycol's mild anesthetic / CNS-depressant -properties as an alcohol.[25] In one case, administration via IV of PG-suspended nitroglycerin to an elderly man may have induced coma and acidosis.[26]

According to a 2010 study by Karlstad University, the concentrations of PGEs, propylene glycol and glycol ethers in indoor air, particularly bedroom air, has been linked to increased risk of developing numerous respiratory and immune disorders in children, including asthma, hay fever, eczema, and allergies, with increased risk ranging from 50% to 180%. This concentration has been linked to use of water-based paints and water-based cleansers.[27][28][29]


Propylene glycol is an approved food additive for dog food under the category of animal feed and is generally recognized as safe (GRAS[30]) for dogs.[31] Similarly, propylene glycol is an approved food additive for human food as well.[32] The exception is that it is prohibited for use in food for cats because of a species-specific reaction in the body, as noted in 21 CFR 582.1666.

Veterinary data indicate that propylene glycol is toxic to dogs with a 50% chance of being lethal at doses of 9mL/kg, although the figure is higher for most laboratory animals (LD50 at levels of 20mL/kg).[33]

However, propylene glycol may be toxic to cats in ways not seen in other animals. The U.S. Food and Drug Administration has determined that its presence in or on cat food has not been shown by adequate scientific data to be safe for use. Any such use is considered an adulteration of the cat food and a violation of the Federal Food, Drug, and Cosmetic Act.[34]

Allergic reaction

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.[35]

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.[36] Post menopausal women who require the use of an estrogen 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.

Additionally, some electronic cigarette users who inhale propylene glycol vapor may experience dryness of the throat or shortness of breath . As an alternative, some suppliers will put Vegetable Glycerin in the "e-liquid" for those who are allergic (or have bad reactions) to propylene glycol.

A Swedish study published in 2010 strongly suggests a connection between airbourne concentrations of propylene glycol in houses and development of asthma and allergic reactions, such as rhinitis, in children.[37]

Possible air germicide

Studies conducted in 1942 by Dr. Oswald Hope Robertson of University of Chicago's Billings Hospital showed vaporized propylene glycol inhalation in laboratory mice may prevent pneumonia, influenza, and other respiratory diseases. Additional studies in monkeys and other animals were undertaken to determine long-term effects, especially the potential for accumulation in the lungs. After a few months of treatment, no ill effects were discovered.[38]


Propylene glycol is known to exert high levels of biochemical oxygen demand (BOD) during degradation in surface waters. This process can adversely affect aquatic life by consuming oxygen aquatic organisms need to survive. Large quantities of dissolved oxygen (DO) in the water column are consumed when microbial populations decompose ethylene glycol.

The oxygen depletion potential of airport deicing operation discharges is many times greater than that of raw sewage. For example, before application, Type I propylene glycol-based deicing fluid is generally diluted to a mixture containing approximately 50% propylene glycol. Pure propylene glycol has a five-day biochemical oxygen demand (BOD5) concentration of approximately 1,000,000 mg/L. A typical diluted propylene-based deicing fluid could therefore have a BOD5 concentration of approximately 500,000 mg/L. In comparison, raw sewage typically has a BOD5 concentration of approximately 200 mg/L. The amount of fluid used to deice a single jet depends on the nature of the precipitation event and the size of the aircraft but can range from several hundred to several thousand gallons. Therefore, deicing a single jet can generate a BOD5 load greater than that of one million gallons of raw sewage. A large hub airport often has several hundred flights each day.

Sufficient DO levels in surface waters are critical for the survival of fish, macroinvertebrates, and other aquatic organisms. If oxygen concentrations drop below a minimum level, organisms emigrate, if able and possible, to areas with higher oxygen levels or eventually die. This effect can drastically reduce the amount of usable aquatic habitat. Reductions in DO levels can reduce or eliminate bottom-feeder populations, create conditions that favor a change in a community’s species profile, or alter critical food-web interactions.[39]

Corexit implications

The chemical is an ingredient in the oil dispersant Corexit, used in great quantities during the Deepwater Horizon oil spill.[5][6] Corexit has come under scrutiny for probable adverse effects on marine life and humans that are exposed to it. Propylene glycol has also come under scrutiny, as it is the chemical that disperses Corexit and the oil to subsurface depths.

See also


  1. ^ Merck Index, 11th Edition, 7868.
  2. ^ "1,2-Propanediol".,2-Propanediol.php. Retrieved 2007-12-28. 
  3. ^ Chauvel, Alain; Lefebvre, Gilles. Petrochemical Processes (Volume 2: Major Oxygenated, Chlorinated and Nitrated Derivatives). Editions Technip. pp. 26. ISBN 978-2-7108-0563-4. 
  4. ^ 1,2-propanediol: chemical product info at CHEMINDUSTRY.RU
  5. ^ a b "Safety Data Sheet Product Corexit EC9527A". Retrieved 2010-05-16. 
  6. ^ a b "Chemicals Meant To Break Up BP Oil Spill Present New Environmental Concerns". ProPublica. Retrieved 2010-05-07. 
  7. ^ "Janusz Szajewski, MD , Warsaw Poison Control Centre (August, 1991). "Propylene glycol (PIM 443)". IPCS INChem. Retrieved July 2, 2009. 
  8. ^ "Antifreeze & Coolant, Gallon". West Marine. 
  9. ^
  10. ^ "Propylene Glycol Freezing Point". XYdatasource. 2010. 
  11. ^ Hamilton, D. J. "Gastric Dyspepsia." The Lancet. Volume 2 1890: p306.
  12. ^ "Material Safety Data Sheet Propionaldehyde MSDS". 2010. 
  13. ^ Miller DN, Bazzano G (1965) Propanediol metabolism and its relation to lactic acid metabolism. Ann NY Acad Aci, 119: 957-973.
  14. ^ Ruddick JA (1972) Toxicology, metabolism, and biochemistry of 1,2-propanediol. Toxicol App Pharmacol, 21: 102-111.
  15. ^ Flanagan RJ;Braithwaite RA;Brown SS;Widdop B;de Wolff FA;. The International Programme on Chemical Safety: Basic Analytical Toxicology. WHO, 1995.
  16. ^ National Library of Medicine;.Propylene glycol is used in antifreezes Human Toxicity Excerpts: CAS Registry Number: 57-55-6 (1,2-Propylene Glycol). Selected toxicity information from HSDB. 2005.
  17. ^ 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.
  18. ^ Agency for Toxic Substances and Disease Registry (2008). Addendum to the Toxicological Profile for Propylene Glycol. pp. 7. 
  19. ^ "DOW: Product Safety Assessment (PSA): Propylene Glycol". Retrieved 2011-11-09. 
  20. ^ A Guide to Glycols (, page 36.
  21. ^ 1,2-Dihydroxypropane SIDS Initial Assessment Profile (, UNEP Publications, SIAM 11, U.S.A, January 23–26, 2001, page 21.
  22. ^ Title 21, U.S. Code of Federal Regulations. 1999.
  23. ^ Szajewski, Janusz. "Propylene Glycol (PIM 443)." 1991. 2 Jun. 2010
  24. ^ Speth PAJ, Vree TB, Neilen NFM et al (1987) Propylene glycol pharmacokinetics and effects after intravenous infusion in humans Ther Drug Monit, 9: 225-258.
  25. ^ Seidenfeld MA, Hanzlik PJ (1932) The general properties, actions, and toxicity of propylene glycol. J Pharmacol, 44: 109.
  26. ^ Demey H, Daelmans R, DeBroe ME et al (1984) Propylene glycol intoxication due to intravenous nitroglycerin. Lancet 1: 1360.
  27. ^ Everyday Substances Increase Risk of Allergies in Children, Swedish Study Reveals, ScienceDaily (Oct. 19, 2010)
  28. ^ Chemical Compounds Emitted From Common Household Paints and Cleaners Increase Risks of Asthma and Allergies in Children
  29. ^ Choi, Hyunok; Norbert Schmidbauer, Jan Sundell, Mikael Hasselgren, John Spengler, Carl-Gustaf Bornehag (2010-10-18). "Common Household Chemicals and the Allergy Risks in Pre-School Age Children". PLoS ONE 5 (10): e13423. doi:10.1371/journal.pone.0013423. PMC 2956675. PMID 20976153. Retrieved 2010-11-17. 
  30. ^ See Wikipedia article on Generally Recognized As Safe
  31. ^ See Code of Federal Regulations: 21 CFR 582.1666
  32. ^ See Code of Federal Regulations: 21CRF184.1666
  33. ^ Peterson, Michael; Talcott, Patricia A. (2006). Small animal toxicology. St. Louis: Saunders Elsevier. pp. 997. ISBN 0-7216-0639-3. 
  34. ^ See 21 CFR 589.1001
  35. ^ American Medical Association, Council on Drugs (1994). AMA Drug Evaluations Annual 1994 (Chicago, Illinois: American Medical Association): 1224. 
  36. ^ Elizabeth Vliet MD, Screaming To Be Heard: Hormonal Connections That Women Suspect and Doctors Ignore". M. Evans and Company, Inc. New York 1995
  37. ^ (Choi, Schmidbauer m.fl. ("010): Common Household Chemicals and the Allergy Risks in Pre-School Age Children. PLoS ONE 5(10): e13423, doi:10.1371/journal.pone.0013423.)
  38. ^ "Air Germicide". TIME. Time, Inc.. 1942-11-16.,9171,932876,00.html. Retrieved 2009-05-23. 
  39. ^ Environmental Impact and Benefit Assessment for Proposed Effluent Limitation Guidelines and Standards for the Airport Deicing Category, July 2009 EPA PDF

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