Obagi-C Fx C-Clarifying Skin-brightening Serum with Vitamin C Formulated with 4% Arbutin and 10% L-Ascorbic Acid to help minimize the appearance of skin aging for a brighter complexion. The Obagi-C Fx C-Clarifying Serum is a part of the Obagi-C Fx System (sold separately). The Obagi-C Fx System products are ideal for improving the appearance of: Fine lines and wrinkles, dull complexion and photoaging.