Kojic acid
Brightener: inhibits tyrosinase, fades dark spots.
What the evidence says
Human evidence (often combined); can sensitize at high strength.
How to use it
Best at night, at 1–2% concentrations, and always with daytime sunscreen (without SPF, no brightener works). Patch test first: it's one of the actives most prone to causing allergic sensitization with continued use.
What it pairs with
It's usually formulated with niacinamide, vitamin C or arbutin, and the combination beats any of them alone. Avoid stacking it with strong exfoliants the same night if your skin is sensitive.
Frequently asked questions
Does kojic acid work for melasma?
Clinical trials (including a 2024 RCT) show improvements, almost always in combination with other brighteners. Melasma is stubborn and relapses with sun exposure: kojic acid helps, but daily sunscreen is half the treatment.
How long until I see results?
Dark spots respond slowly: allow 8–12 weeks of consistent use before judging. If persistent itching or redness appears at any point, stop — kojic acid sensitization doesn't improve by pushing through.