Gradually diminishes dark spots with 4% hydroquinone, and provides Vitamins C and Vitamin E to your skin while you sleep.With Obagi-C Rx, you’re on your way to healthier, refreshed, revitalized skin from cell to surface. Obagi-C Rx Systems promote skin rejuvenation from the inside out using a formulation of prescription-strength hydroquinone USP, 4%, which reduces the appearance of hyperpigmentation and age spots, combined with 10% L-Ascorbic Acid (Vitamin C)the only topical antioxidant proven to stimulate collagen synthesis and protect your skin by minimizing future skin cell damage.