We carry five different strengths for different skin types:Vitamin C 10%- for sensitive skin,Vitamin C 15%- for dry skin, Vitamin C 20%- for all skin types,Vitamin C 25%- for oily or mature skin or skin with clogged pores, andHigh Potency Vitamin C 25% pH 5- for extremely sensitive skin (those too sensitive for pH 3.5). Many leadings scientists highly recommend applying vitamin C onto the face daily to protect against UV-induced cell damage. This sun damage not only causes premature aging, but also many forms of skin cancer. Vitamin C has many other beneficial properties, including being one of the few ingredients that has a scientific base to show that it reverses signs of aging for your skin. Vitamin C (L-Ascorbic acid) has been shown to stimulate collagen, decrease wrinkle depth, and have lightening effects on pigmentation.Hyaluronic acid, also known as HA, is a natural compound found in skin that has many important functions, including holding in moisture, providing cushioning, aiding in tissue repair, holding together the skin's structural components (collagen and elastin), and helping create a protective barrier against microorganisms. Vitamin C Serum 25% with pure hyaluronic acid is effective at moisturizing skin cells, which prevents water loss and protects the skin from dirt and other pollutants. Hyaluronic acid delivers AND holds water in the skin. Hyaluronic acid based products are considered extremely safe. There are few allergic reactions or side effects involved with using hyaluronic acid, though some people may experience a mild, temporary redness or swelling after an injection. We keep our product for topical use only so as to reduce the chances of this! Repeated use of hyaluronic acid will maintain moisture levels in the skin, preventing skin dehydration.