Professional-C Serum Vitamin C 20% Antioxidant Defense is Obagi's bestselling vitamin C serum, formulated with L-Ascorbic Acid and Sodium Hyaluronate for a supercharged, hydrated glow that doesn't quit - at home or on the road. One full-size bottle for your everyday routine, one travel-size for wherever the day takes you. | Obagi Medical Brightening Duo: Professional-C Serum 20% | Dermstore