Obagi Professional-C Serum 20% infuses your skin with L-ascorbic acid, the only form of vitamin C suitable for topical application. Designed to penetrate deep into your skin, this vitamin C serum provides effective antioxidant protection from UV damage as it brightens away hyperpigmentation and encourages the growth of collagen and elastin fibers. Hyaluronic acid binds moisture to your skin to prevent dryness.