Professional-C Serums use advanced formulas developed and tested by leading Vitamin C experts. They offer maximum daily antioxidant protection and greater penetration than other Vitamin C products. The greater the penetration, the greater the antioxidant benefit to your skin

If you're a beginner, start with 5% concentration that's also safe for use around the eyes. Once you're ready to take a step up, try the 10% or 15% serum (10% is better for dry or sensitive skin). Then, if your skin is stubborn and needs a stronger approach, move up to 20%.