What it does
Pure L-ascorbic acid is the best-studied form and the most temperamental. It oxidises on contact with light and air, which is why good formulas come in opaque or airless packaging and why a bottle that has turned dark orange is telling you it is finished. If your vitamin C serum smells metallic and looks like weak tea, throw it out.
Used in the morning under sunscreen, it works as a partner to UV protection rather than a replacement for it. The visible payoff is on tone and dullness over eight to twelve weeks, not overnight glow.
At the 15–20% concentrations that work, the low pH stings a meaningful number of people. Derivatives such as sodium ascorbyl phosphate or ascorbyl glucoside are far gentler and more stable, with a weaker but real effect — a fair trade if pure ascorbic acid burns.
In a routine
Layers well with
- Vitamin E
- Ferulic acid
- Sunscreen
Do not layer with
- Benzoyl peroxide
Same routine is fine for some pairs — same step is the problem. Split them morning and evening when in doubt.
