DEFY C+ Serum | 1ozDual Source Vitamin C. Ferulic Acid. CBD. The Brightening Protocol That Actually Works. Most Vitamin C serums fail for one of two reasons: the Vitamin C is unstable and oxidizes before it reaches the skin, or it's delivered in a single form that can't penetrate both the water and lipid layers of the skin barrier. DEFY C+ solves both problems. Two forms of stabilized Vitamin C one oil soluble, one water soluble work simultaneously across both phases of