Neutriherbs Vitamin C Lip Treatment Smooth Cream Neutriherbs SA 5 Powerful Benefits of Vitamin C Serum on Lips Bright Idea Vitamin C Serum SkinCeuticals Antioxidant Lip Repair Vitamin C serum can be used either in the morning or night and even twice a day. , If you apply retinol at night, then use vitamin C serum in the morning. If you only use a moisturiser at night, then Vitamin C Serums Explained: Benefits, Myths, and Science Backed Result