One of the most widely used vitamins in cosmetic products is ascorbic acid (vitamin C). The popularity is based partly on the critical physiological role it plays as an antioxidant in various biochemical processes, and is general accepted by the public as providing various health benefits. Relative to skin, its greatest impact is upon collagen synthesis as well as its antioxidant properties. In dermal fibroblasts, it serves as a cofactor for both prolyl hydroxylase and lysyl hydroxylase, key enzymes that posttranslationally hydroxylate proline and lysine residues in Types I and III collagen as part of the posttranslational processing of procollagen, ultimately impacting the integral structural properties of collagen fibrils upon assembly into the final bundled quartenary structure [19,20]. In addition, the antioxidant properties of ascorbic acid make it very attractive to be used topically to help block potential surface damage from oxygen radicals induced by UV and other environmental insults. Since the connection between oxygen radical damage of skin’s surface and aging has been well-established [21], the usage of topical antioxidants to combat UV-induced damage has always been an appealing and compelling cosmetic ingredient story. What has not been as well-established however is whether the antioxidants can lead to any significant noticeable change in the aging skin’s appearance.
While the usage of topical ascorbic acid is intriguing because of the biochemistry, there are significant limitations which appear to mute some of the anticipated efficacy. These limitations include poor skin penetration, instability due to rapid oxidation, and formulation compatibility with other components in finished products. Attempts to overcome these limitations and thereby increase availability have spurred the development of analogues, which include ascorbyl phosphate (as the magnesium and sodium salts), ascorbyl palmi – tate, and ascorbyl glucoside.
Several clinical studies have been published discussing the antiskin-aging benefit of ascorbic acid [22]. Relative to fine lines and wrinkles, a stabilized 3% ascorbic acid applied topically was found to be well tolerated by the skin, and it reduced facial wrinkles as determined by skin replica analysis [23]. In another study, 17% vitamin C (10% as ascorbic acid and 7% as tetrahexyldecyl ascorbate) in an anhydrous gel was found to reduce facial photoaging, as determined by dermatologist grading [24]. From a histological assessment of biopsy specimens, there was improvement in net collagen by an increased Grenz zone.
In summary, topical ascorbic acid and the various analogues can be shown to have some modest effects against photodamaged facial skin endpoints, but are not considered robust agents for fine line and wrinkle benefits compared with other technologies available to consumers [ 25 ].