Glycerin vs Propylene Glycol (Cosmetic): which is worse?

What is Glycerin?

Glycerin is a simple polyol (sugar alcohol) that is colorless, odorless, and viscous. It naturally occurs in all animal and vegetable fats and is the backbone of triglyceride molecules. Cosmetic glycerin is typically derived from vegetable oils (plant-based) or as a biodiesel byproduct.

What is Propylene Glycol (Cosmetic)?

Propylene glycol is a small synthetic organic compound (diol) used in cosmetics as a humectant, solvent, and skin-conditioning agent. It is produced from propylene oxide (petroleum) but also from bio-based sources.

Documented risks

Glycerin: Glycerin is one of the safest cosmetic ingredients known, with centuries of use. The CIR has repeatedly confirmed its safety. It is non-irritating, non-allergenic, and non-toxic. At very high concentrations in leave-on products (>30%), it can have a dehydrating paradox effect — pulling water from the dermis if the environment is very dry — but this is not a health risk. It is safe for all ages including infants.

Propylene Glycol (Cosmetic): Propylene glycol is safe at typical cosmetic use concentrations (1–15%). The CIR and EU SCCS have both reviewed and affirmed its safety. It can cause contact sensitization and irritant reactions in some individuals, particularly at concentrations above 5% in leave-on products; those with sensitive or compromised skin may react. It is rapidly metabolized if absorbed and is not bioaccumulative. There is no evidence of carcinogenicity or endocrine disruption at cosmetic use levels. Note: this entry covers topical cosmetic use; ingested large doses (antifreeze context) are toxic, which is a separate matter.