Can you use niacinamide and vitamin C together?

The warning against combining them comes from 1960s research on conditions your bathroom will never reproduce. Here is what the pairing actually does on skin.

The claim that niacinamide cancels out vitamin C traces back to mid-century studies where the two were heated together in solution and formed niacin, a compound that can cause flushing. Those conditions — high temperature, extreme pH, long duration — do not describe a serum applied to a face.

In modern finished formulas the pairing is stable and common. Niacinamide is comfortable across a broad pH range, and L-ascorbic acid is formulated at a low pH for penetration; layering them a minute apart, or using a product that contains both, is well tolerated by most skin.

They also address different problems, which is the real argument for using both. Vitamin C is an antioxidant that interrupts free-radical damage and supports collagen synthesis. Niacinamide supports barrier lipids, regulates sebum and reduces the transfer of pigment to skin cells. Together they cover antioxidant defence and pigmentation from two directions.

The practical caveat is tolerance rather than chemistry. High-strength L-ascorbic acid at 15–20% can sting on reactive skin, and niacinamide above roughly 5% causes flushing in a minority of users. If you react, separate them — vitamin C in the morning, niacinamide at night — and you lose nothing.

For anyone shopping in the EU, both ingredients appear on the INCI list under fixed names: Niacinamide, and Ascorbic Acid or a derivative such as Sodium Ascorbyl Phosphate or Tetrahexyldecyl Ascorbate. Position on that list tells you more about the strength than the number printed on the front.