What it is: A powerful vitamin C serum now formulated with even more vitamin C, that visibly reduces fine lines and wrinkles. What it does: Kiehl's original formula, infused with 10.5% pure vitamin C, now has an additional 2% of vitamin Cg for increased potency. Vitamin Cg is a vitamin C derivative that activates once absorbed into the upper layers of the skin's surface and is used in anti-wrinkle skin care products to help reduce facial lines over time. Fragmented hyaluronic acid has also been added to this formula to help instantly smooth skin. Through clinical studies, this serum has been shown to help decrease the appearance of fine lines and wrinkles and improve skin radiance and texture, even helping to reduce the appearance of forehead lines, marionette lines and deep-set wrinkles after four weeks of regular use.