Niacinamide

If you only ever add one active to your routine, make it niacinamide. Vitamin B3 does several useful things at once — fades post-blemish marks, regulates oil, strengthens the barrier, calms redness — and it does them without the irritation tax that acids and retinoids charge.

Most Korean formulas sit between 2% and 10%. Higher is not better; 5% is plenty for tone, and very sensitive skin often does best at 2%.

The old warning about never mixing it with vitamin C is a myth from a 1960s study using unstable raw ingredients. In modern formulas they work well together. Pair it with sunscreen for dark spots.

Want the longer version? Read Niacinamide: the one ingredient every skin type needs.