Gluconolactone (GDL) powder is a multifunctional polyhydroxy acid (PHA) primarily used in skincare for gentle exfoliation, intense hydration, and anti-aging benefits, suitable for sensitive skin. It acts as a humectant, antioxidant, and pH adjuster in lotions, serums, and masks, often used at 1–15% in formulations. It also serves as a food-grade coagulant (tofu), leavening acid, and preservative.