Before I go into this, yes, I know that I sell a vitamin C serum. (And a damn good one too!) That said, this fact does not make me a completely biased writer — if I found convincing evidence that vitamin C serums were in fact bad for your skin, I would immediately pull it from the market, and replace it with something else. (It’s not that hard to do, honestly.) So, please, I am going into this as unbiased as I can.
Now, with that said, there was an article on the Oumere blog promoting the idea that vitamin C serums are bad for your skin. The article claimed that vitamin C serums are pro-oxidant, reactive with copper/phosphates/EDTA, and will work for a short time and then stop working. A reader asked me to debunk the article, or at least share my thoughts on it.
Vitamin C Serums Do Not Become Pro-Oxidant, Antioxidants Just Decay
If not stabilized, vitamin C and other antioxidants can become oxidized upon prolonged exposure to light or air, turning brown. This brown color leads people to think that the vitamin C serum may be pro-oxidant and damaging to the skin, but this is not the case.
Each molecule of vitamin C contains two electrons available for use. When the first is used, the resulting molecule actually becomes more stable than other free radicals and can serve as a free-radical scavenger. After loss of a second electron, the resulting oxidation product, dehydroascorbic acid, can be regenerated or may decay (Journal of the American Academy of Dermatology, 2003).
If twice-oxidized vitamin C (dehydroascorbic acid) is applied topically to the skin, the skin cells will reduce some of the compound back to vitamin C (Journal of Biological Chemistry, 1995). However, some of dehydroascorbic acid will also decay. Chemists know decay has occurred when the molecule’s lactone ring irreversibly opens, so this is traceable in actual studies. I have yet to encounter a study demonstrating application of decayed dehydroascorbic acid has any negative effect.
To summarize again, the rumor pro-oxidant vitamin C becomes damaging to the skin comes from the idea antioxidants absorb free radicals; after a certain point, they must be supersaturated and release free radicals instead. However, when vitamin C absorbs free radicals, it becomes dehydroascorbic acid, and then decays.
Vitamin C Does NOT Have a Tachyphlaxis-Like Effect (Decreasing Over Time)
Vitamin C is a water-soluble vitamin that is both created and metabolized by your cells. Once vitamin C is used, more is needed for cells to function properly.
Take scurvy, for instance. Scurvy can lead to anemia, debility, exhaustion, spontaneous bleeding, and even death (Medical News Today). Its cause is a deficiency in vitamin C. If vitamin C did in fact produce a tachyphylaxis-like effect, with the same dose causing less collagen to be produced over time not only in our skin but in our internal organs and blood vessels as well, we would all be screwed. Instead, supplementing with vitamin C throughout your life has been shown to keep scurvy (and other signs of vitamin C deficiency) at bay.
Vitamin C Does React with Other Compounds
One point I do agree with the Oumere blog post about is that vitamin C can react with other compounds.
I don’t worry that much, though, about vitamin C with what are typically trace amounts of ingredients like EDTA, copper, or phosphate.
On the other hand, I personally do not use niacinamide with vitamin C. Unlike EDTA, copper, or phosphate, niacinamide is generally present in quality skincare products in concentrations of 1-5%.
Although the Paula’s Choice blog and others disagree with me, I don’t dispute the literature — In the presence of UV light and oxygen, the two compounds combined (L-ascorbic acid and niacinamide) may generate pro-oxidant hydrogen peroxide. This is not a reaction that needs a very high temperature or a ton of UV light to be induced, either.
Secondly, niacinamide and vitamin C neutralize one another. When mixed together in aqueous solutions (since both are water-soluble vitamins), they form a 1:1 complex that turns the solution yellow, rendering both compounds useless.
Lastly, niacinamide works best at a slightly higher pH range (4.5-5.5) than vitamin C (4.5 and under). So I prefer to use them separately.
While I have full respect for the Oumere blog, Paula’s Choice, and others I have disagreed with in this article, I believe that vitamin C serums are one of the best tools you can have for brighter, tighter skin. And I also believe that you shouldn’t use vitamin C serums with niacinamide, but aside from that, I don’t worry too much about combining them with much else.