Propylene Glycol
Propylene Glycol (PG) is a colorless liquid with CAS# 57-55-6. Its primary role in cosmetic formulations is to improve freeze-thaw stability, ensuring products do not freeze or melt at extreme temperatures, typically used at less than 2% for this purpose. It also functions as a humectant, solvent for other ingredients, and a mild penetration enhancer at higher concentrations (10–25%). It is listed as a food-safe additive and is used in injectable drugs, indicating a well-established safety profile at low concentrations.
At low concentrations (under 5%), PG helps skin attract and retain moisture as a humectant and aids in dissolving and stabilizing other cosmetic ingredients. It may enhance the penetration of certain beneficial actives into the skin, though significant penetration enhancement requires concentrations of 10–25%, which are rarely used in cosmetics.
Can be a skin irritant when used in pure (100%) form or at concentrations above 10%; concentrations above 10% may cause irritation. Often criticized in natural cosmetics communities, though cosmetic scientists and toxicology experts consider it safe at typical use levels below 5%.
