Obagi-C RX System C-Clarifying Serum 1oz. Obagi C-Clarifying Serum works to even skin tone and reduce the appearance of fine lines and wrinkles resulting in smoother, more radiant skin. Directions For Use: A thin application should be applied daily to the affected area.As with all Obagi products, we encourage you to see a medical professional to determine if these products are right for you. We do not recommend purchasing these products without a medical professional''s recommendation and strongly encourage you to continue to follow up with your physician on a regular basis. Ingredients: Each gram of Obagi-C Rx System C-Clarifying Serum contains Hydroquinon USP 40 mg/gm in a base of propylene glycol, propylene carbonate, L-ascorbate acid (Vitamin C), purified water and sodium lauryl sulfate.