Obagi-C Clarifying Serum is a patented formulation that combines 10% vitamin C (L-Ascorbic acid) with 4% hydroquinone. It gradually brightens and evens skin tone resulting in more radiant skin. Penetrates deep into the skin's dermal layers, where it enhances collagen production and reduces melanosome activity and tyrosinase activation. Skin becomes smoother and brighter with each use. Vibrant, younger-looking skin can be yours with the skin-brightening and antioxidant-rich formula of Obagi-C Rx C-Clarifying Serum. This serum is designed to lighten, strengthen, and clarify the tone, texture, and overall appearance of skin. It penetrates deep into the skin without irritation to enhance collagen production and reduce hyperpigmentation. Directions: Apply a thin layer daily to the affected area. Ingredients: Hydroquinone USP 40mg/gm in a base of purified water, cetyl alcohol, glycerin, sodium lauryl sulfate, stearyl alcohol, tocopheryl acetate, asorbic acid, sodium metabisulfite, lactic acid, saponins, disodium EDTA, methylparaben, BHT, propylparaben and butylparaben.