Proven

Vitamin C

Antioxidant; brightens, evens tone and supports collagen synthesis.

What the evidence says

Effective but unstable; L-ascorbic acid at 10–20% is the best-proven form.

Best forDull, spot-prone skin (AM)
INCI namesAscorbic Acid · L-Ascorbic Acid · 3-O-Ethyl Ascorbic Acid · Ascorbyl Glucoside · Ascorbyl Tetraisopalmitate
Evidence basisPullar et al., 2017 (Nutrients)

How to use it

In the morning, on clean skin, before moisturizer and sunscreen: as an antioxidant it complements SPF by neutralizing the free radicals that sun and pollution generate through the day. Keep the serum sealed, dark and cool — the pure form oxidizes with light and air.

What it pairs with

Pairs very well with sunscreen (additive photoprotection), vitamin E and ferulic acid (which stabilize it) and niacinamide. Avoid using it in the same session as strong exfoliants or retinoids if your skin is sensitive.

Frequently asked questions

Which form of vitamin C is best?

L-ascorbic acid at 10–20% is the form with the most clinical evidence, but it's unstable and can irritate. Derivatives (ascorbyl glucoside, 3-O-ethyl ascorbic acid — common in K-beauty) are more stable and gentler, in exchange for less direct evidence.

Vitamin C in the morning or at night?

Morning gets the most out of its antioxidant role: under sunscreen, it helps neutralize UV and pollution damage. It also works at night for dark spots and tone — consistency is what matters.

Can I combine vitamin C with niacinamide?

Yes. The supposed incompatibility comes from 1960s studies using unstabilized forms at high temperatures. With modern formulas they can be used together without issue, and their effects on spots and tone are complementary.

How do I know if my vitamin C serum has oxidized?

By its color: if an L-ascorbic acid serum turns from clear or pale yellow to dark orange or brown, it has oxidized and lost much of its potency. Time to replace it.

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