Propylene Glycol
What It Is
Propylene glycol — 1,2-propanediol, CH3CH(OH)CH2OH (CAS 57-55-6) — is a synthetic organic compound, a clear viscous liquid that is hygroscopic and miscible with water. It is produced industrially from propylene oxide derived from petroleum or, increasingly, from bio-based glycerol via dehydration. Propylene glycol functions as a humectant (moisture-attracting agent), solvent, preservative booster, and viscosity reducer.
Common Uses
Propylene glycol appears in moisturizers, deodorants, makeup, shampoos, hair conditioners, liquid hand soaps, household cleaning sprays, pharmaceutical preparations (as a solvent for IV medications), food (as a stabilizer in salad dressings, frostings, and processed foods, where it carries the E number E1520), and electronic cigarette liquids. Its versatility and low cost have made it one of the most-used synthetic humectants in consumer products globally.
How It Works
Propylene glycol's three-carbon backbone with two hydroxyl groups gives it both water-loving and oil-loving character, which is why it functions as a solvent for ingredients that do not dissolve in water alone. As a humectant, the hydroxyl groups attract water molecules from the surrounding environment, helping personal care formulations retain moisture on skin or hair. As a preservative booster, it lowers the water activity of a formulation, making it harder for microorganisms to grow and allowing the primary preservative to work at lower concentrations.
Safety and Regulation
The U.S. FDA designates propylene glycol as Generally Recognized as Safe (GRAS) for food use under 21 CFR 184.1666. The Cosmetic Ingredient Review (CIR) Expert Panel concluded that propylene glycol is safe as a cosmetic ingredient at concentrations up to 50% in most product categories (CIR, 1994; reaffirmed). However, contact sensitization to propylene glycol is well documented. The American Contact Dermatitis Society named propylene glycol "Allergen of the Year" in 2018, citing its high rate of positive patch-test reactions in dermatology clinics — roughly 3.5% of patch-tested patients react to a 30% propylene glycol patch (Warshaw et al., Dermatitis, 2018). The European Cosmetics Regulation permits propylene glycol without specific concentration limits but requires it to be listed on ingredient labels when present.
Why Natural Flower Power Does Not Use It
Natural Flower Power does not use propylene glycol in any product.
The functional role propylene glycol plays — humectant, solvent, viscosity adjuster — is filled in our formulations by vegetable glycerine, derived from plant oils. Vegetable glycerine delivers comparable moisture attraction and solvent properties, with a substantially lower contact-sensitization rate and a plant-derived sourcing pathway that aligns with our formulation standards. The American Contact Dermatitis Society's 2018 "Allergen of the Year" designation for propylene glycol reinforced a choice we had already made on supplier and formulation grounds — but it does illustrate why "GRAS" or "CIR-safe" classifications do not always translate into a clean experience for sensitive customers.
Related Ingredients
Vegetable glycerine is the plant-derived humectant Natural Flower Power uses instead of propylene glycol. SD Alcohol 40B is a solvent we use in specific product categories. Polysorbate 20 is a non-ionic emulsifier we use for essential-oil dispersion in water-based products.
Sources
- U.S. Food and Drug Administration. "Substances Generally Recognized as Safe: Propylene Glycol." 21 CFR 184.1666.
- Cosmetic Ingredient Review (CIR) Expert Panel. "Final Report on the Safety Assessment of Propylene Glycol and Polypropylene Glycols." International Journal of Toxicology, vol. 13, 1994, pp. 437–491.
- Warshaw, E.M., et al. "Patch Testing with Propylene Glycol — The American Contact Dermatitis Society Allergen of the Year 2018." Dermatitis, vol. 29, no. 1, 2018, pp. 3–5.
- European Commission. Regulation (EC) No 1223/2009 on Cosmetic Products. Ingredient labeling requirements.
