Glycols on a Toner or Essence Label, Explained: What Butylene Glycol, Propanediol and Pentylene Glycol Do, and What the CIR Safety Reviews Concluded
Open a Korean toner or essence and the first lines often read water, glycerin, butylene glycol, propanediol or pentylene glycol. This guide covers what these glycols do in a formula and what the Cosmetic Ingredient Review (CIR), the expert panel that publishes cosmetic safety assessments, wrote about them.
What "glycol" means on a label
In cosmetics, glycol is a family name for small molecules with two hydroxyl groups, also called diols. The CIR lists them as solvents, humectants and skin-conditioning agents. Humectants hold water.
Butylene glycol: the long-standing one
The CIR assessed butylene glycol (1,3-butanediol) in 1985 and reaffirmed the conclusion in 2006: safe as used. That wording applies to the uses and concentrations the panel reviewed, not to every person.
Propanediol: the corn-derived option
Propanediol is 1,3-propanediol. The CIR's 2018 final report says it can be made from corn-derived glucose by fermentation. It had 1,528 reported uses in FDA registration data, the most of the ten diols reviewed, and a 2015 survey put the highest level at 39.9% in non-spray deodorants. The panel concluded it is safe as used.
Pentylene glycol: humectant and preservative helper
Pentylene glycol (1,2-pentanediol) was judged safe as used in 2012. The CIR notes it also works as a preservative, with use reported at up to 5% in a 2010 survey. A foundation containing 0.112% of it showed no potential for irritation or sensitization in a patch test on 101 subjects. The same report mentions a case of facial dermatitis from an eye cream containing it, so rare reactions exist.
What the human tests on propanediol showed
Undiluted propanediol was non-irritating after a single application. At 5% to 75% it was non-sensitizing, with mild redness in 4 of 207 subjects at 75% during induction. Those are test concentrations, not what a toner contains. The report adds that none of its diols, propanediol included, are restricted under EU cosmetic rules.
Propylene glycol is a different molecule
Propylene glycol (1,2-propanediol) carries different wording from the CIR: safe as used when formulated to be non-irritating (2012). Formulation matters as well as the ingredient name.
Where they sit in a routine
These humectants usually sit in the first steps. Our toner before essence guide explains that order, and the skin flooding guide covers humectants on damp skin. For another humectant, see the glycerin guide.
Before you try a new bottle
Labels list ingredients in descending order but print no percentages, so a glycol line says little about dose. This guide summarizes published safety reviews and does not diagnose or treat any skin condition. Patch test any new product first, using our patch test guide, and see a dermatologist about persistent reactions.
All content is fact-checked under our editorial standards.