Chapter 9: Solvents and hydrocarbons · Part 2: Glycols and helpers
Propylene glycol
- Made from a hazardous chemical
- Contaminant risk
The worst fact: US dermatologists named it Allergen of the Year for 2018: it's a weak skin allergen and an irritant. In large doses it causes acid build-up and kidney injury: in one US intensive-care study, 4 of 21 patients (19%) on intravenous sedatives made with it showed metabolic signs of propylene glycol toxicity, though none became clinically worse. The US says it isn't shown to be safe in cat food.
Why brands use it: it keeps liquids clear and stable, protects enzymes, and stops the product freezing or drying out.
Take care if: you have eczema or a known allergy to it. Europe's medicines agency sets lower safety thresholds in medicines for children under 5 (50 mg/kg a day) and newborns (1 mg/kg a day).
Comes from: propylene oxide and water. A chemistry reference calls this the only industrial process, though it can also be made from glycerol. Australia classes propylene oxide as "May cause genetic defects; May cause cancer". That doesn't mean it's in the product, but it's not a great starting point for something you clean with.
Myth check: "It's antifreeze, so it's poison": it's used to make some antifreeze, but the US health agency says it doesn't form the harmful crystals that ethylene glycol does, and it's an approved food additive in Australia (1520).
Contaminants: diethylene glycol and ethylene glycol. In 2022, Indonesian authorities found both in a propylene glycol ingredient used in children's syrups. It was part of a wave of contaminated syrups across at least seven countries that the WHO linked to more than 300 deaths in three of them, mostly children under five. The US limit for medicine-grade propylene glycol is 0.10%. They're unlikely in a well-made product, but it's a factor you can't see on the label.
Fair to say: the harmful cases are from large medical doses in vulnerable patients, not from cleaning. A US government review found "negligible concern" for effects on fertility or development.
Correct as of November 2026. What the badges mean
Sources
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for each chemical, and for ethylene oxide, propylene oxide, epichlorohydrin, benzene, 1,3-butadiene-containing butane and 1,2-dichloroethane. Workplace exposure standards (amended November 2025) and workplace exposure limits (July 2025). Labelling of workplace hazardous chemicals code of practice (2015). Trichloroethylene health monitoring guide.
- Food Standards Australia New Zealand. Food Standards Code, Schedule 8 (2025).
- European Medicines Agency. Propylene glycol used as an excipient (EMA/CHMP/704195/2013, 2017).
- US FDA. Testing of glycerin, propylene glycol and other high-risk drug components for DEG and EG (2023); 21 CFR 184.1666; 21 CFR 589.1001.
- ATSDR. ToxFAQs: 2-butoxyethanol; propylene glycol; toluene; xylenes.
- US National Toxicology Program. Technical Report 464: sodium xylenesulfonate (1998); Report on Carcinogens, 15th edition; NTP-CERHR monograph on propylene glycol (2004).
- OECD. SIDS initial assessment: propylene glycol ethers (SIAM 17, 2003).
- WHO. Medical product alerts on contaminated paediatric medicines (2022–2023); statement of 23 January 2023.
- HSDB (US National Library of Medicine), via PubChem: manufacturing, use and impurity data.
- HERA. Propylene glycol n-butyl ether (2005); hydrotropes (2005).
- Jacob SE, Scheman A, McGowan MA. Propylene glycol: Allergen of the Year 2018. Dermatitis 2018;29:3-5.
- Wilson KC et al. Propylene glycol toxicity in ICU patients receiving IV benzodiazepines. Chest 2005;128:1674-1681.
The full source list is at the end of Chapter 9.