Vitamin C is a skin‘s own ingredient and functions as a major hydrophilic antioxidant. It is an essential micro-nutrient, that cannot be synthesized by the human body and has to be taken up by the diet (main source: fruits and vegetables). Vitamin C neutralizes free radicals and thereby protects skin from oxidative stress (ROS, reactive oxygen species) provoked by external stressors such as UV light and pollution. An imbalance of the antioxidative system can lead to oxidative damage of macromolecules such as DNA, lipids and proteins. Besides its antioxidant function vitamin C is an essential cofactor in collagen synthesis.