Propylene Glycol

What it is

Propylene glycol is a small synthetic alcohol used for decades as a humectant, a solvent for ingredients that will not dissolve in water, and a preservative booster. It is also a food additive and a carrier in many oral and injectable medicines. It is frequently confused with ethylene glycol, the toxic component of engine antifreeze; they are different molecules with very different safety profiles.

What it does well

• Hydrates and helps dissolve other active ingredients

  Propylene glycol binds water and is one of the most reliable solvents in cosmetic chemistry, letting formulators include actives and preservatives that would otherwise be difficult to stabilise.

  Strong evidence

• The "it's antifreeze" fear is misplaced

  The dangerous antifreeze compound is ethylene glycol, a different chemical. Propylene glycol is approved as a food additive in the EU and used as a solvent in licensed medicines. Toxicity concerns relate to large ingested or intravenous doses, not topical cosmetic use.

  Strong evidence

Worth knowing

• Documented contact allergen, though sensitisation rates are low

  The American Contact Dermatitis Society named propylene glycol its Allergen of the Year for 2018. However, the largest patch-test dataset (45,138 patients) found only 2.3% positive reactions, with many of those judged likely false positives, and concluded that propylene glycol has very low sensitisation potential on intact skin.

  Matters most toPeople with known propylene glycol allergy, and those with chronic leg dermatitis or long-standing eczema, where sensitisation is more likely.

• Can irritate or sting at higher concentrations

  Explicit irritant reactions occurred in 0.6% of patch-tested patients. Irritation is dose-dependent and more likely on already-damaged skin than on healthy skin.

  Matters most toPeople with compromised or actively inflamed skin.

Where the EU stands

Sources (3)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   Skin-sensitizing and irritant properties of propylene glycol

   Contact Dermatitis · 2005 · doi:10.1111/j.0105-1873.2005.00693.x

   Across 45,138 patch-tested patients, 2.3% reacted positively and 0.6% showed irritant reactions; the authors concluded propylene glycol has very low sensitisation potential on uncompromised skin.

2. [2]
   Propylene Glycol

   Dermatitis (American Contact Dermatitis Society) · 2018 · doi:10.1097/DER.0000000000000315

   The article accompanying propylene glycol's designation as ACDS Allergen of the Year 2018, describing it as both a sensitiser and an irritant and discussing correct patch-testing methods.

3. [3]
   Allergic contact dermatitis from propylene glycol: A case series from Australia

   Contact Dermatitis · 2023

   A recent case series confirming that genuine allergic contact dermatitis to propylene glycol occurs and is worth patch testing for, while remaining uncommon.