Vitamin C, explained

The classic antioxidant for brightness and firmness. What it does for skin over 40, which form to choose and how to keep it from going off.

Good evidence

What it does

Vitamin C is an antioxidant that helps protect skin from sun and pollution damage, and the skin needs it to make collagen. It also helps fade dark spots and gives a brighter look.

Why it suits skin over 40

Years of sun exposure show up as dullness, uneven tone and loss of firmness. Vitamin C works on all three, and it pairs well with daily sunscreen in the morning.

Which form?

L-ascorbic acid

The most researched form, usually at 10 to 20%. Effective but can sting and goes off quickly once opened.

Gentler derivatives

Ascorbyl glucoside, sodium ascorbyl phosphate, tetrahexyldecyl ascorbate and ethyl ascorbic acid. More stable and kinder to sensitive skin, but with less research. Common in Korean serums.

How to use it

Apply in the morning after cleansing, then moisturiser and sunscreen.
Start every other day if your skin is sensitive.
Keep it cool and closed. If a clear serum turns dark orange or brown, it has oxidised.
It’s fine with niacinamide. Keep strong vitamin C and acids on different times of day.

What the research shows

In a six-month, double-blind trial, women with sun-damaged skin applied a 5% vitamin C cream to one side and a plain cream to the other. Both dermatologists and the volunteers saw a significant improvement on the vitamin C side, with smoother skin texture and fewer deep furrows.

Humbert and colleagues, Experimental Dermatology, 2003 [1]

Our take: vitamin C is one of the best-researched actives for brighter, firmer-looking skin after 40. Use it in the morning under sunscreen, choose a gentle derivative if your skin is sensitive, and replace it if it changes colour.

Compare prices: Vitamin C

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Compare prices for Beauty of Joseon Light On Serum Centella + Vita Cfrom £17.53 delivered

Good to know

Should I use vitamin C in the morning or at night?

Morning is ideal, under sunscreen, because it helps protect against daily damage. Night is fine too if mornings are rushed.

Can I use vitamin C with retinol?

Yes, but at different times: vitamin C in the morning and retinol or retinal at night.

Why has my vitamin C serum turned orange?

It has oxidised from air, light or heat, and works less well. Replace it, and store the next one somewhere cool and dark.

Sources

Humbert PG et al. Topical ascorbic acid on photoaged skin. Clinical, topographical and ultrastructural evaluation: double-blind study vs. placebo. Exp Dermatol. 2003;12(3):237-44.

This page is general information, not medical advice. Last updated 30 October 2026.