You can. The rule against it has been repeated so often that it has the texture of fact, but it comes from 1960s laboratory work in which pure ascorbic acid and pure niacinamide were combined under heat — conditions that produced niacin, which can cause flushing. Those are not the conditions inside a modern, pH-balanced, stabilised serum, and they are certainly not the conditions on your face.
What the two actually do is complementary, which is why they appear together in so many well-composed routines. Vitamin C is an antioxidant: it lifts dullness, softens the look of dark spots, and adds daytime defence. Niacinamide is a quiet multitasker: it evens the look of tone, refines the appearance of pores, supports the barrier and helps temper oil. One brightens; the other steadies.
How to layer them: cleanse, apply the thinner texture first, wait about thirty seconds, then the second. In practice that usually means vitamin C then niacinamide, then moisturiser, then sunscreen. That thirty-second pause is not ceremony — it is what stops products pilling and rolling off each other.
The honest caveat: a small number of people do find the combination tingles, particularly at high concentrations of both. That is worth respecting rather than pushing through. If it happens to you, split them — vitamin C in the morning, niacinamide at night. You lose nothing, because both work cumulatively rather than in the moment.
And if your skin is currently reactive, stinging at things it used to tolerate, the answer is not to rearrange the order of your actives. It is to stop them for a fortnight and let the barrier settle. Layering questions only matter once the skin underneath is calm.
The rule was real once. It stopped being true the moment formulas stopped being laboratory experiments.
