The concentration of vitamin C in the serum is higher than the face oil. That means the vitamin C serum will be much more effective at brightening the skin and reversing the signs of aging. The main job of a face oil is to improve hydration, but if brightening the skin, reducing dark spots, decreasing the signs of aging, decreasing melasma or scarring are your main goals, you’ll want the Vitamin C serum rather than the Brightening Oil.