Butylene Glycol

Butylene glycol is a small-molecule glycol used as humectant, solvent, and penetration enhancer in a huge share of serums and essences. It dissolves both water- and some oil-soluble actives, helping them distribute evenly and absorb better. As a humectant it draws modest moisture to the skin while giving formulas a light, elegant slip. Decades of safety data and clinical patch testing show it is far less irritating than its reputation in some corners of the internet suggests — it is well tolerated at typical 1–10% levels. Rare sensitivity exists, as with any ingredient. It is a formulation workhorse, not a star — but it makes the stars perform better.