Vitamin C is available in a variety of forms, but none are to absorb as effectively as L-Ascorbic Acid (pure vitamin C). In clinical studies, derivatives of ascorbic acid including magnesium ascorbyl phosphate, ascorbyl-6-palmitate, and dehydroascorbic acid have not been shown as effective. All SkinCeuticals antioxidants are formulated with pure l-ascorbic acid in accordance with the Duke Antioxidant patent.