All Vitamin C is not created equal. That's why we created this treatment with clinical strength 10% Tetrahexyldecyl (THD) Ascorbate, a highly penetrable, more efficacious, and less irritating form of Vitamin C that diminishes the look of dark spots and defends against skin-aging free radical damage. Unlike other Vitamin C products on the market, ours is formulated without water to ensure longer product stability to optimize your skin brightening, smoothing, and radiance-boosting benefits. Layer under your SPF for an antioxidant boost or apply after moisturizer to lock in softness and brightness.