Transforming Vitamin C Obagi Professional-C Serum vitamin C neutralized free radicals at all layers of the skin, before they damage skin cells and accelerate aging. Obagi Professional-C serum offers a superior delivery system, resulting in greater penetration to all layers of the skin, maximum daily antioxidant protection and greater stability than competitive C products. Benefits to the skin included maintaining normal cellular turnover, building collage, lightens and brightens the skin, reduces inflammation and decreases trans-epidermal water loss. Obagi Professional-C Serum is specially formulated to use as a once-daily, stand alone product, or for use within the Obagi Nu-Derm System. Obagi Professional-C Serum is available in 4 concentrations.