OBAGI C-Clarifying Serum (Dry to Normal skin) contains the antioxidant Vitamin C (10% L-Ascorbic Acid) and prescription-strength hydroquinone. This patented formulation reduces the appearance of dark spots for a lighter, brighter complexion. Benefits: Builds collagen and delivered powerful antioxidant benefits. Clinically proven to improve skin color. Offers great stability even after opening. Powerful anti-oxidant. Provides better penetration than the leading competitors vitamin C serum.