In short, kinda...
Vitamin C is a veritable wonder ingredient for skin and its benefits are plenty; but to deliver all its goodness effectively, the vitamin needs to be in the potent, and unstable form, known as L-ascorbic acid. But how long is it's shelf life?
Vitamin C, famous for being found in citrus fruits, is an antioxidant, (see you later environmental ageing), it’s a collagen builder (hello voluminous skin) and it’s a skin tone brightener (welcome youthful glow).
Vitamin C is by way of association, often as is thought of as orange, but in reality, vitamin C dissolved into water is not orange at all. It’s clear. As clear as water.
Which in turn means, your Vitamin C serum should also be clear.
If you're a Vitamin C veteran, you'll know that the potency of your serum has more weight than just the L-ascorbic acid percentage, but also about its bioavailability, i.e. how well the overall formula delivers the goodness to your skin and the shelf life of the product.
With a skincare ingredient like Vitamin C, it may well be stable for three years in a closed bottle, but when it’s opened daily for use, the shelf-life now becomes in-use life and the three-year shelf life expectation goes out the window.
Vitamin C is such an effective anti-oxidant, its chemistry isn't limited to skin-contact. As soon as the product is opened, it's active in the bottle and the compounds begin to change.
This is exactly what happens when Vitamin C serums turn brown. Vitamin C has oxidised (reacted with oxygen) and turned into dehydro-L-ascorbic acid and eventually diketogulonic acid.
The yellow-brown colour change is a visual sign of chemistry change. It shows that your Vitamin C serum no longer just contains L-ascorbic acid, the skin active form of the vitamin.
So, In Short...
The more Vitamin C there is in your serum, the clearer it will be. The more ‘oxidation products’ there are in your Vitamin C serum the more brown it will be, meaning less of serum's benefits are available for your skin – oxygen from the air has gotten to them first.
While the oxidisation of Vitamin C can't be stopped, it can be slowed down through limiting its exposure to heat, light and air.
- Heat - It's not essential to refrigerate your Vitamin C serum but it help to prolong its in-use life.
- Light - Try minimise through storing in a draw or in shade.
- Air - After use, replace the lid quickly and tightly.