⨠SkinCeuticals C E Ferulic Serum â 1 fl oz | New & Sealed in Box. 0.5% Ferulic Acid â Boosts stability and effectiveness of vitamins. Product Type: Antioxidant Serum. Size: 1 fl oz (30 ml). 15% L-Ascorbic Acid (Vitamin C) â Brightens and improves skin tone.