Using Vitamin C and Niacinamide together, Vitamin C and Oxidation: From Our Mailbag

Q: Hi there. I have been using your Vitamin C, E and Ferulic acid serum and love it, but have recently watched some youtube videos saying that you shouldn’t combine niacinamide with vitamin C. I’m a bit worried now, please can you help? Thanks, H

A: Hi H,

I can’t speak to what the youtube videos say, but I know that Vitamin C has been thoroughly studied clinically and niacinamide as well, with well-known safety profiles. If you’re really concerned, of course, speak with a dermatologist, but here are some of the more well-known studies about these ingredients
Some people have been concerned that when these two ingredients combine, that they can create skin irritation or just plain cancel each other out. Probably the most thorough explanation I’ve seen is this article. The writer, Stephen Alain Ko, is a cosmetics chemist, and does an excellent job of explaining the science and why it’s actually a good idea to combine Vitamin C and Niacinamide:
He also goes on to explain that when Niacinamide and Vitamin C are combined, they create a natural light yellow tint, which will look very different from a rust orange that it would take on if the vitamin C is oxidized, and therefore, kind of useless.
Here’s a picture I took of what our Vitamin C is supposed to look like (left) and what happens when it’s left out in the sun for few hours on a paper plate and oxidizes. It also kinda dried out, and some crystals formed, but the color difference is what I’m trying to point out:
Also these:

Ferulic acid stabilizes a solution of vitamins C and E and doubles its photoprotection of skin

Final report of the safety assessment of niacinamide and niacin