As one of the Obagi Professional-C Serums, this serum contains the highest percentage of vitamin C (L-ascorbic acid). At 20% concentration of vitamin C, this is a strong yet gentle serum that is intelligently formulated to combat the signs of ageing and hyperpigmentation. Topical application of vitamin C in the Obagi-C serums not only protects your skin from UV related damage and enhanced ageing, it plays a vital role in collagen production in your skin. Collagen is responsible for your skin's firmness and elasticity and so Obagi Professional-C 20% is designed to improve skin’s plumpness and promote a healthy youthful glow.