Product name: butylene glycol

CAS: 26171-83-5

Molecular formula: C₄H₁₀O₂

Molecular weight: 90.121

Description: Butylene glycol is a chemical compound (1,3-butanediol)—a colorless organic alcohol used in the following ways:

as a solvent (helps other products dissolve in water),

as a viscosity-decreasing agent (to thin creams and gels so they’re easier to use),

and as a conditioning agent.

You can find it listed on the product labels of hair care products, moisturizers, foundations, sunscreens, eye creams, mascaras, and more. It’s also used as a food additive to add flavoring—it has a sweet flavor and a bitter aftertaste—and in the manufacture of polyester plasticizers, structural material for boats, custom moldings, and sheets and boards for construction.

When placed on the skin or ingested, butylene glycol is absorbed and broken down into “gamma-hydroxybutryic acid,” a naturally occurring compound found in humans. The Cosmetic Ingredient Review (CIR), the FDA, and the World Health Organization have all found butylene glycol to be safe.