An ester of vitamin A (retinoic acid) and vitamin C (ascorbic acid) that functions as an antioxidant that seems to have a particular affinity for skin and its lipids, making it an effective topical option for improving skin's defense against environmental damage. This mix also shows greater stability in skin than when retinol or vitamin C are used alone.
References for this information:
Pharmazie, October 2005, pages 794-795
Skin Pharmacology and Physiology, November-December 2004, issue 6, pages 274-282
International Journal of Pharmaceutics, August 2004, issues 1-2, pages 113-124