Vitamin C Serum | COSRX The Vitamin C 13 Serum is a brightening serum formulated with 13% pure Vitamin C (Ascorbic Acid) to fade dark spots, even out skin tone, and improve overall radiance. Enriched with Vitamin E and Hyaluronic Acid, it nourishes, hydrates, and soothes the skin while protecting it from environmental damage. Lightweight and fast-absorbing, this serum is ideal for daily use to achieve a clear, glowing, and healthy complexion.