The Glow Maker Antioxidant Serum featuring Vitamin C plus E Ferulic Acid Serum - Lightweight - 1 fl oz

As a skin-care ingredient, vitamin C is really hard to stabilize, so be aware that over time your product may begin to oxidize. Oxidized vitamin C becomes less effective over time and in some cases can cause a darkening or discoloration effect. Pay attention to the color of your serum—if it starts to turn orange or brown, it’s oxidized. Also, be sure to pay attention to the expiration date on your product, and know that, typically, L-ascorbic acid has about a three-month shelf life once the bottle is opened.