Pentylene Glycol
Also known as 1,2-Pentanediol, Pentane-1,2-diol, Hydrolite 5
“CIR Expert Panel says: safe as used in cosmetics.”
Pentylene Glycol (1,2-pentanediol; CAS 5343-92-0; C5H12O2) is a C5 alkane-1,2-diol used in cosmetic formulations as a humectant, solvent, and preservative booster. It is one of four members of the 1,2-glycol series in current cosmetic use (alongside caprylyl glycol, 1,2-hexanediol, and C15-18 glycol), and sits in the middle of the series by chain length. Pentylene glycol is commonly used as a preservative booster in combination with phenoxyethanol or organic-acid preservatives because it enhances antimicrobial efficacy and allows lower total preservative concentrations, and separately as a humectant and penetration enhancer in lightweight hydrating formulations. The Cosmetic Ingredient Review Expert Panel reviewed pentylene glycol together with 15 other 1,2-alkane-diols and concluded they are safe in the present practices of use and concentration described in the assessment (Johnson, Bergfeld, Belsito et al., Int J Toxicol 31(5 Suppl):147S-168S, 2012, PMID 23064773). The Panel noted that dermal absorption of 1,2-glycols occurs but decreases for longer-chain members of the series; pentylene glycol is shorter-chain than caprylyl glycol so absorption is somewhat greater, but combined with negative oral toxicity, genotoxicity, and irritation data on the shorter-chain homologues the Panel judged the safety margin adequate. The QRT row carries no conditions or concentration limits.
Preservative booster that enhances phenoxyethanol and organic-acid preservative efficacy, enabling lower total preservative concentrations
Humectant and solvent commonly used in K-beauty toners, essences, and serums for lightweight texture
CIR Expert Panel concluded safe as used in cosmetics (Johnson et al., IJT 2012, PMID 23064773) — same assessment also clears caprylyl glycol, 1,2-hexanediol, and C15-18 glycol
Penetration enhancer useful for improving the dermal delivery of water-soluble actives in lightweight formulations
- · Contact allergy reports are uncommon at typical cosmetic use levels
Small aliphatic diols (including pentylene glycol) are dermally absorbed; the CIR 2012 assessment relied on modeling and oral toxicity data rather than dedicated dermal kinetics studies on pentylene glycol specifically
CIR Quick Reference Table (12/2017, revised 07/2018) - Pentylene Glycol row: Finding 'S' (Safe), Citation 'IJT 31(S2):147-168, 2012'
“Pentylene Glycol | S | [no detail column entry] | IJT 31(S2):147-168, 2012”— QRT-122017revised072018.pdf, p. 100