This serum, which is made for brighter, firmer, and overall better-looking skin, contains 10% vitamin C. Vitamin C antioxidants shield the skin from UV rays and help to prevent dark spots, resulting in skin that is vibrant and bright. Using serum is the best way to incorporate this potent substance into your skincare regimen. Applying a few drops in the morning before using a moisturizer helps shield the skin all day.