Methylpropanediol
Also known as 2-Methyl-1,3-propanediol, MPD, 2-Methyltrimethylene glycol
“CIR Expert Panel says: safe as used in cosmetics.”
Methylpropanediol (2-methyl-1,3-propanediol; CAS 2163-42-0) is a branched C4 alkane diol used in cosmetics as a solvent and humectant, with 541 reported uses in FDA VCRP data as of 2017. The CIR Expert Panel reviewed it as part of a 10-ingredient alkane diol group assessment and concluded it is safe in the present practices of use and concentration (IJT 43(Suppl. 2):70S-131S, 2024; PMID 38174390). Supporting toxicology data from Fowles et al. (2017; PMID 29097239) confirmed low acute toxicity (LD50 >5 g/kg in rats), negative genotoxicity (Ames and chromosomal aberration tests), no mutagenicity, and a favorable biodegradation profile. Human skin irritation studies showed the compound was non-irritating at 100% and 50% aqueous dilution in 14-day cumulative studies. Methylpropanediol is rapidly metabolized to 3-hydroxybutyrate and excreted with a short half-life of approximately 3.6 hours.
Effective solvent and humectant with high water solubility and low toxicity profile
Rapidly biodegradable with low environmental hazard (log Kow -0.6; low bioaccumulation potential)
Non-irritating to skin at cosmetic use concentrations in human patch studies
Negative genotoxicity in multiple in vitro and in vivo assays
Well-studied metabolism: rapidly converted to 3-hydroxybutyrate, a normal metabolite, with short half-life
Mild sensitization potential observed in guinea pigs at high concentrations (up to 100% at challenge) and mixed results in some human sensitization studies, though CIR Panel concluded overall non-sensitizing profile
Alkane diols can enhance dermal penetration of co-formulated ingredients; CIR Panel noted care should be taken when formulating with other ingredients for which safety is based on lack of dermal absorption
CIR Safety Assessment of Alkane Diols as Used in Cosmetics (Tentative Report April 2017; Final published IJT 43(Suppl. 2):70S-131S, 2024)…
“Methylpropanediol (2-Methyl-1,3-Propanediol)”— ADIOLS042017TR.pdf, p. 17