Hexylene Glycol
Also known as 2-Methyl-2,4-pentanediol, 4-Methyl-2,4-pentanediol, MPD, Diolane
“CIR Expert Panel says: safe as used in cosmetics.”
Hexylene Glycol (2-methyl-2,4-pentanediol; CAS 107-41-5; C6H14O2) is a branched C6 aliphatic diol used in cosmetic formulations as a humectant, solvent, and coupling agent. Unlike the 1,2-positioned diols (caprylyl glycol, 1,2-hexanediol), hexylene glycol carries hydroxyl groups at the 2 and 4 positions with a methyl branch at C2, giving it different physicochemical properties — in particular, lower antimicrobial activity than the 1,2-glycol series and greater industrial use as a coupling solvent for coatings and hydraulic fluids. In cosmetics it is used at low concentrations (typically 0.1–2%) as a humectant, co-solvent, and fragrance carrier. The Cosmetic Ingredient Review Expert Panel assessed hexylene glycol together with butylene glycol, ethoxydiglycol, and dipropylene glycol and concluded all four glycols are safe as cosmetic ingredients in the present practices of use (J Am Coll Toxicol 4(5):223-48, 1985; reaffirmed without reopening the assessment in 2004, republished Int J Toxicol 25(Suppl 2):1-26, 2006). The QRT row carries no conditions or concentration limits. Hexylene glycol is distinct from 1,2-hexanediol (hexane-1,2-diol; CAS 6920-22-5), which is in the separate 1,2-glycols group assessment (IJT 31(S2):147-168, 2012).
Humectant that draws and retains moisture in the stratum corneum; useful in lightweight hydrating formulations
Solvent and coupling agent that improves compatibility and spreadability of active ingredients in complex formulations
CIR Expert Panel concluded safe as used in cosmetics:223-48, 1985; reaffirmed 2004) — same assessment also clears butylene glycol, ethoxydiglycol, and dipropylene glycol
Branched C6 diol structure contributes to good skin feel and formulation stability in emulsion and hydrogel systems
- · Mild to moderate skin irritation reported in animal patch tests at high concentrations; not a clinical concern at typical cosmetic use levels (CIR 1985)
- · Distinct from 1,2-hexanediol (hexane-1,2-diol) — researcher confusion is common due to similar naming; different molecule, different CIR assessment, different functional profile
Hexylene glycol has significant industrial applications as a solvent and coupling agent; at industrial concentrations it is an irritant — these data should not be extrapolated to cosmetic use concentrations
CIR Quick Reference Table (12/2017, revised 07/2018) - Hexylene Glycol row: Finding 'S' (Safe), Citation 'JACT 4(5):223-48, 1985 confirme…
“Hexylene Glycol | S | [no detail column entry] | JACT 4(5):223-48, 1985 confirmed 02/04 IJT 25(S2):1-26, 2006”— QRT-122017revised072018.pdf, p. 56