Propylene Glycol
Also known as 1,2-Propanediol, Propane-1,2-diol, Methyl ethylene glycol, alpha-Propylene glycol, PG
“CIR Expert Panel says: safe within use limit.”
Propylene Glycol (1,2-propanediol; CAS 57-55-6; C3H8O2) is a small aliphatic diol — the 1,2-regioisomer of propanediol — and one of the most historically widespread humectant/solvent ingredients in cosmetics and pharmaceutical formulations. Despite carrying 'propylene' in its common name, it is chemically distinct from propylene and is structurally a glycol (two hydroxyl groups on adjacent carbons). In cosmetic formulations it functions as a humectant, solvent for water-soluble and moderately lipophilic actives, viscosity decreasing agent, and fragrance carrier. The Cosmetic Ingredient Review Expert Panel originally assessed propylene glycol in 1994 (J Am Coll Toxicol 13(6):437-91) and concluded it is safe in cosmetic products at concentrations up to 50%. The 2012 re-review (Fiume, Bergfeld, Belsito et al., Safety Assessment of Propylene Glycol, Tripropylene Glycol, and PPGs as Used in Cosmetics, Int J Toxicol 31(5 Suppl):245S-260S, 2012, PMID 23064775) reaffirmed the 50% concentration limit and extended the safety determination to tripropylene glycol and the polypropylene glycol (PPG) series. Propylene glycol is generally non-toxic and non-carcinogenic; clinical studies showed no dermal sensitization at typical use concentrations, though skin irritation at high concentrations has been reported and contributed to the 50% cap. The QRT SQ finding with '50%' Detail reflects this concentration cap — concentrations above 50% are not within the safety conclusion. Propylene glycol is FDA GRAS as a direct food additive and widely used in pharmaceutical formulations as a solvent for injectable and oral drugs (including many common medications). It is also used industrially as a non-toxic antifreeze where its low toxicity makes it safer than ethylene glycol.
Effective humectant and solvent with a long history of use in cosmetics and pharmaceuticals — one of the most widely-used functional ingredients across personal care
FDA Generally Recognized As Safe (GRAS) as a direct food additive; approved pharmaceutical excipient for oral and injectable drug formulations
CIR Expert Panel concluded safe in cosmetic products at concentrations up to 50%:437-91, 1994; reaffirmed Fiume et al. IJT 2012, PMID 23064775) — same assessment also clears tripropylene glycol and the polypropylene glycol series
Solvent for lipophilic and hydrophilic actives; enables formulation of fragrance, flavor, and active ingredients that are poorly water-soluble
Freezing-point depressant and cryoprotectant — also used industrially as non-toxic antifreeze in food-contact applications
Dermal irritation reported at high concentrations (above 50%); the CIR 50% concentration cap explicitly addresses this — formulations above 50% propylene glycol are not covered by the CIR safety conclusion
Contact dermatitis occurs in a small subset of patch-test patients, particularly with leave-on applications on compromised skin; propylene glycol is a well-known 'sensitive skin' irritant and is sometimes excluded from hypoallergenic formulations for this reason
Distinct from propanediol (1,3-propanediol) — they are different regioisomers with different assessments and different natural-derivation profiles; propylene glycol is commonly petrochemical-derived while propanediol is commonly plant-fermentation-derived
CIR Quick Reference Table (12/2017, revised 07/2018) - Propylene Glycol row: Finding 'SQ' (Safe Qualified) with Detail '50%', Citation 'J…
“Propylene Glycol | SQ | 50% | JACT 13(6):437-91, 1994; IJT 31(2) 245-260, 2012”— QRT-122017revised072018.pdf, p. 112