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

What is Butylene Glycol?

Butylene glycol (1,3-butanediol) is a small diol used in cosmetics as a humectant, solvent, and skin-conditioning agent. It is closely related to propylene glycol but has a slightly larger molecular structure, often making it even better tolerated.

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

Butylene Glycol: Butylene glycol has a good safety profile and is better tolerated by sensitive skin than propylene glycol at equivalent concentrations. The CIR has confirmed it safe for cosmetic use. It is non-carcinogenic, non-mutagenic, and not an endocrine disruptor. Contact sensitization is rare. It is widely used in Korean beauty (K-beauty) formulations as a preferred humectant.

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.