The 10% serum if for dry, sensitive, or reactive skin. In the proper form and potency, vitamin C attacks free oxygen radicals. In addition to its function as a powerful antioxidant, vitamin C also encourages the production of collagen and elastin. Used daily, vitamin C products can help restore the luster and youthfulness that time has taken away. Vitamin C contains L-ascorbic acid, the most potent form of vitamin C available, and the only form of vitamin C the body uses to combat oxy-radicals. 1 fl oz.