Vitamin C (L-Ascorbic Acid) is next to hyaluronic acid one of the most popular cosmetic ingredients at the moment. Why? because people see actual results when using products such as serums containing this ingredient. The thing to look for with vitamin C is it is not very stable. Think of when you eat an appl and you can’t finish it immediately starts to turn brown. This is the Vitamin C oxidizing It’s not stable in light and in the air. Recent studies have taught us that Vitamin C likes to be mixed together with other antioxidants such as Vitamin E and is now a popular addition to stabilize Vitamin C is Ferulic acid. Having said all this it is best to use your Vitamin C as quickly as possible. 2X a day will help and always top up with a face cream. Also, it is better to find a company that allows you to add your vitamin C FRESH when you are ready to use it. Vitamin C is easily soluble so this takes little effect for big fresh results.