Stable, water-soluble form of vitamin C that functions as an antioxidant. This form of vitamin C is also potentially effective for brightening an uneven skin tone, although there isn’t much research supporting its use for this purpose over other forms of vitamin C.
References for this information:
Journal of Photochemistry and Photobiology, August 2009, pages 130-135
International Jounal of Cosmetic Science, December 2008, pages 453-458