Q: Can I use Vitamin C if it has oxidized?

In short: Surprisingly, yes. But it won’t be very effective.

So, if your vitamin C serum has turned orange/brown, it’s likely that the main component has oxidized. This process is usually accelerated by exposure to air and light, and it often happens with L-ascorbic acid and Ascorbic acid forms. When vitamin C oxidizes, it loses both of its electrons (normally, it has two). As a result, it converts into dehydroascorbic acid (DHA). This oxidized form can partially convert back to vitamin C and partially degrade.

Is a serum with oxidized vitamin C useless?

According to the authors of a study in the Journal of Biological Chemistry, when DHA (oxidized vitamin C) is applied to the skin, cells can restore some of it back to vitamin C. However, some of the DHA will also degrade. What does this mean? A certain percentage of vitamin C will penetrate the skin, but you would achieve more noticeable results with “fresh” non-oxidized serum. There are some studies suggesting that DHA may penetrate the skin more effectively, but the data is still limited.

Can oxidized vitamin C harm the skin?

We often hear warnings that oxidized vitamin C accumulates free radicals and “injects” them into the skin, promoting aging. Fortunately, that’s not how it works. When vitamin C absorbs free radicals, it simply converts into DHA. As for DHA’s potential harm when applied topically, there is no scientific evidence to support this. It seems that oxidized vitamin C is simply less effective, but not dangerous.