Obagi-C Fx C-Clarifying Serum 1 Fl. Oz - Brighten and Revitalize Your Skin. Skin brightening. New in box. Sealed. Non-comodogenic, allergy tested. Fx C-Clarifying Serum formulated with 4% arbutin and 10% L-ascorbic acid to help minimize the appearance of skin aging for a brighter complexion.