Propylene glycol, also known as 1,2-propanediol or propane-1,2-diol, is an organic compound and a type of diol (a double alcohol). Its chemical formula is C₃H₈O₂ or HO-CH₂-CHOH-CH₃. It’s sometimes referred to as α-propylene glycol to distinguish it from its isomer, propane-1,3-diol (HO-(CH₂)₃-OH), also known as β-propylene glycol.
At room temperature, propylene glycol appears as a clear, colourless, slightly syrupy liquid. Although it can exist in air as vapour, it needs to be heated or shaken vigorously to do so. It is practically odourless and tasteless.
What is Propylene Glycol used for?
About 45% of the propylene glycol produced is used as a chemical feedstock for making unsaturated polyester resins. It reacts with a mix of maleic anhydride and isophthalic acid to create a copolymer. This copolymer is then further cross-linked to form thermoset plastics.
Propylene glycol also reacts with propylene oxide to produce oligomers and polymers, which are used in the production of polyurethanes.
Other key uses include:
As a humectant (E1520), solvent, and preservative in food and tobacco products
A main ingredient in e-liquids for electronic cigarettes (alongside vegetable glycerine and occasionally PEG 400)
A solvent in pharmaceuticals and personal care products
In injectable drug formulations like diazepam and lorazepam (as they are water-insoluble)
In aircraft de-icing fluids and automotive antifreeze, due to its ability to lower water’s melting point
A minor ingredient in the oil dispersant Corexit, used extensively during the Deepwater Horizon oil spill
Propylene Glycol is used as a solvent in personal care products.
Sources and Routes of Exposure
Sources of Exposure
You may be exposed to propylene glycol through:
Eating food that contains it
Using cosmetics with it
Taking medications that use it as a solvent
Working in industries that use propylene glycol or products that contain it—through inhalation or skin contact
Routes of Exposure
The main ways propylene glycol enters the body include
Inhalation
Ingestion
Skin contact
Eye contact
Health Effects
Exposure to propylene glycol may cause the following health effects:
Slight, temporary eye injury
Harmful absorption through damaged or abraded skin; allergic reactions have been reported
A single, long exposure to skin is unlikely to be harmful; prolonged contact is generally non-irritating, but repeated exposure may cause problems
Animal studies in guinea pigs consistently showed negative results for sensitisation—propylene glycol is not considered an occupational skin sensitiser
Ingestion may cause nausea, vomiting, diarrhoea, and gastrointestinal irritation
May cause hemoglobinuric nephrosis
May cause changes in surface EEG (brain activity)
Inhalation of mist may irritate the respiratory tract
Due to its low vapour pressure at room temperature, vapour exposure is unlikely
Chronic exposure to high doses may lead to central nervous system depression
Chronic ingestion may cause lactic acidosis and possible seizures
No adverse effects reported for pregnant women—no expected effects on the foetus
Birth defects are considered unlikely
Animal studies show no interference with reproduction
Not classified as a carcinogen by DHHS, IARC, or EPA
Animal studies have not shown propylene glycol to be carcinogenic
Safety
First Aid Measures
Eye Contact: Remove contact lenses if present. Rinse eyes with running water for at least 15 minutes, keeping eyelids open. Cold water may be used. Seek medical attention.
Skin Contact: Flush skin with plenty of water immediately. Apply an emollient. Remove contaminated clothing and shoes. Cold water may be used. Wash clothing before reuse and clean shoes thoroughly. Seek medical attention.
Serious Skin Contact: Wash the area with disinfectant soap and apply an antibacterial cream. Seek immediate medical attention.
Inhalation: Move the person to fresh air. If not breathing, give artificial respiration. If breathing is difficult, provide oxygen. Get medical attention.
Ingestion: Do not induce vomiting unless instructed by medical personnel. Never give anything by mouth to an unconscious person. If large amounts are swallowed, contact a physician immediately. Loosen tight clothing like collars, belts, or waistbands.
Exposure Control & Personal Protection
Engineering Controls
Use exhaust ventilation or other engineering controls to keep airborne vapour levels below their threshold limit. Ensure that eyewash stations and safety showers are near the work area.
Personal Protective Equipment (PPE)
When handling propylene glycol, the following PPE is recommended:
Splash goggles
Lab coat
Vapour respirator (use only approved/certified types)
Gloves
For large spills, additional protection includes
Splash goggles
Full protective suit
Vapour respirator
Boots
Gloves
A self-contained breathing apparatus to prevent inhalation
Standard protective clothing may not be sufficient; consult a specialist before handling large quantities of this substance
Regulation
United States
FDA: The U.S Food & Drug Administration has classified propylene glycol as "generally recognised as safe," which means that it is acceptable for use in flavourings, drugs, and cosmetics, and as a direct food additive.
NIOSH: The National Institute for Occupational Safety & Health has established a time weighted average concentration for propylene glycol of 100 ppm (360 mg/m3).
OSHA: The U.S Occupational Safety & Health Administration has not established a permissible exposure limit for propylene glycol.
Australia
Safe Work Australia: Safe Work Australia has established a time weighted average concentration for an 8-hour workday of 100ppm (369 mg/m3).
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