ABSTRACT
That was the bad news. The good news is that the most effective way to increase the skin level of vitamin C signi‘- cantly is by topical application. To optimize percutaneous absorption and full activity of vitamin C, the precise formulation is of the utmost importance (4). Since L-ascorbic acid is an excellent antioxidant, making it an inherently unstable molecule, creation of an effective topical delivery system is crucial. Many products contain stable esteri‘ed derivatives (such as ascorbyl-6-palmitate or magnesium ascorbyl phosphate) which are not metabolized by the skin to the active ascorbic acid, so they have no activity (5). Furthermore, the ester molecules are not absorbed percutaneously (5). Some of these esteri-‘ed derivatives have been reported to give contact allergy (6,7). Other formulations do not result in measurable absorption of vitamin C because they are not at the correct pH. Delivery of L-ascorbic acid (pKa∆ = 4.2) depends upon removing the ionic charge-achieved optimally at a pH of 3.5 (5). New formulations stabilizing the vitamin C in microcapsules (8), liposomes (9,10), and microemulsions (10) are being investigated for stability, absorption, and activity.
