Vitamin C is the most studied brightening ingredient in skincare, and also the most misused.
What it does
It evens tone, fades marks left by breakouts and protects against daytime damage.
Which strength
Start at 10%. Higher is not better if your skin stings.
How to use it
Morning, on clean dry skin, before moisturiser and sunscreen. Three or four drops are enough.
What not to mix
Keep it away from strong acids in the same routine. Use those at night instead.