There are actually several different forms of Vitamin C that are used in skincare formulas. Vitamin Cg, or Ascorbyl Glucoside, is a potent derivative of Vitamin C that provides antioxidant protection and helps to minimize the visible signs of aging. Our Vitamin C serum is formulated with 2% Vitamin Cg to help enhance the efficacy of Vitamin C benefits over time. While they have overlapping benefits, Pure Vitamin C (L-Ascorbic Acid) is absorbed into skin and starts working immediately upon contact while Vitamin Cg (Ascorbyl Glucoside) activates once absorbed into the upper layers of skin to boost Vitamin C activity over time. Kiehl’s Vitamin C serums and formulas effectively incorporate a form of topical Vitamin C that is carefully selected to maximize its targeted efficacy.