What's the best concentration of vitamin C?

10%–20% L-ascorbic acid for the strongest results. Lower concentrations or derivative forms (sodium ascorbyl phosphate, magnesium ascorbyl phosphate) suit sensitive skin but deliver milder effect.

How can I tell if my vitamin C has oxidised?

It turns yellow, then orange, then brown. Once brown, the vitamin C has lost most of its activity and may even drive irritation. Store in dark glass, keep cool, replace within 3–6 months of opening.

Can I use vitamin C with retinol?

Yes — but in different routines. Vitamin C in the AM (under SPF for antioxidant protection), retinol in the PM. Combining them in the same routine is unnecessary and may increase irritation.

Is vitamin C safe in pregnancy?

Yes. Vitamin C is widely considered pregnancy-safe and is the standard antioxidant active for pregnant users (when retinoids are contraindicated).

Vitamin C in skincare.

Vitamin C in topical skincare is most commonly L-ascorbic acid (the most potent and most-studied form), with derivatives including sodium ascorbyl phosphate, magnesium ascorbyl phosphate, and ascorbyl glucoside (gentler, more stable, but less potent). Effective topical concentrations of L-ascorbic acid range from 5% to 20%. Stability is the chronic challenge — vitamin C oxidises in light and air, turning brown and losing potency.

What it does

Antioxidant — neutralises free radicals from UV exposure and pollution. Brightens skin tone. Fades hyperpigmentation by inhibiting tyrosinase (the enzyme that produces melanin). Supports collagen synthesis. Boosts the photoprotective effect of sunscreen when used together. The standard daytime active in most evidence-based skincare routines.

The evidence

Strong. Multiple decades of peer-reviewed research support vitamin C's antioxidant effects, hyperpigmentation-fading, and collagen-supportive benefits at clinically meaningful concentrations.

Who should use it

Effectively everyone. Particularly useful for users with hyperpigmentation, sun-damaged skin, dullness, or anyone seeking daytime antioxidant support. Useable in pregnancy. Compatible with most other actives.

What it pairs with

Vitamin E and ferulic acid (extends vitamin C stability and boosts antioxidant effect — the SkinCeuticals C E Ferulic formulation is the canonical example). Sunscreen (vitamin C boosts SPF's photoprotective effect). Avoid pairing with retinol in the same routine — use vitamin C AM, retinol PM.

What to buy in Australia

SkinCeuticals C E Ferulic — AU$230, the clinical-tier benchmark. The Ordinary Ascorbic Acid 8% + Alpha Arbutin 2% — AU$15, the affordable entry point. Some By Mi Galactomyces Pure Vitamin C Glow Serum — AU$28, the gentler K-beauty alternative.

Frequently asked questions.

What's the best concentration of vitamin C?: 10%–20% L-ascorbic acid for the strongest results. Lower concentrations or derivative forms (sodium ascorbyl phosphate, magnesium ascorbyl phosphate) suit sensitive skin but deliver milder effect.
How can I tell if my vitamin C has oxidised?: It turns yellow, then orange, then brown. Once brown, the vitamin C has lost most of its activity and may even drive irritation. Store in dark glass, keep cool, replace within 3–6 months of opening.
Can I use vitamin C with retinol?: Yes — but in different routines. Vitamin C in the AM (under SPF for antioxidant protection), retinol in the PM. Combining them in the same routine is unnecessary and may increase irritation.
Is vitamin C safe in pregnancy?: Yes. Vitamin C is widely considered pregnancy-safe and is the standard antioxidant active for pregnant users (when retinoids are contraindicated).