Firstly, the science bit!
It is not critical to the skin because of its antioxidant properties, it is critical to the skin because of the role it plays in your dermis (so important that the products you choose get down to your dermis!) , where it causes a reaction called hydroxylation. This means essentially that it makes all the amino acids link together. When everything is linking our skin is healthy and makes collagen for us. You cannot make collagen with low vitamin C.
THE MILLEN METHOD
#1 Ingredients
So one of the main vitamin C’s that the skin recognises when it is doing the hydroxylation process is L-ascorbic acid. It is a small molecule so it can penetrate the skin. If you add in other products to stabalize it, the less penetration you will get. Another ingredient to look out for is 3-0-Ethyl Ascorbate, again it has the ability to reach your dermis. Vitamin C’s with these ingredients are often expensive, and in this case you do get what you pay for.
#2 What to consider
I don’t think you need to go higher than 10%, this is wounding territory….you don’t want to be wounding your epidermis to get results, and actually how much of the vitamin c content can actually get through to your dermis….this is quite hard to judge.
Stable and oxidised are the key words to look out for too, they give better penetration to the dermis.
#3 My recommendations:
Osmosis Catalyst
Obagi Profession C serum
ZO 10% Vitamin C Self activating.