Brightening booster. Boosters are super concentrated formulas made with a single active ingredient, such as hyaluronic acid, retinol, or vitamin C. This one is turbocharged to instantly stimulate skin and Target specific concerns including pigmentation, dehydration, or breakouts. you can use it alone, or mix it with your serum or moisturizer. Apply your products from lightest to heaviest, and wait a minute in between each one to increase absorption.