Vitamin C or ascorbic acid is an essential nutrient. This water-soluble vitamin is important in humans for a number of reasons especially because of its antioxidant property, its function as a cofactor for importance enzymes and its role in collagen synthesis.itamin C is useful in acne treatment for two major reasons: it serves as an antioxidant and it contributes to collagen synthesis. As an antioxidant, vitamin C removes harmful free radicals and reducing them to harmless compounds.