Vitamin C

Vitamin1–20%

A brightening antioxidant that helps skin look more radiant and even, available in pure and stable forms.

What it is

Vitamin C is an antioxidant that helps the appearance of dullness and uneven tone, so skin looks brighter. It comes as pure L-ascorbic acid, the most researched form, or as gentler derivatives.

Good for

Dull skinUneven toneDark spotsMature skin

How it works

As an antioxidant, vitamin C helps neutralise free radicals created by UV and pollution, and skin uses it in making collagen. It is also thought to slow pigment production, so marks can look lighter over time. Most derivatives must be converted to vitamin C in the skin, and evidence that they work as well is more limited.

Ratings

Evidence

4/5

Good evidence for L-ascorbic acid at 10–20%, less for derivatives.

Gentleness

3/5

Low-pH L-ascorbic acid can sting, while derivatives are gentler.

Formulation difficulty

4/5

L-ascorbic acid oxidises quickly in water-based formulas.

Cost

3/5

Ascorbic acid is cheap, but stabilising systems and packs add cost.

Popularity

5/5

Consistently among the five most-searched skincare ingredients.

Pairs and cautions

Pairs well with

In a routine. Pairing in one formula depends on matching pH windows.

Vitamin E
Ferulic acid
Daily sunscreen
Hyaluronic acid
Niacinamide

Take care with

Copper peptides in the same productCopper speeds oxidation

Formulations it suits

Serum Cream Lotion Cream or sleeping mask

Packaging

Regional considerations

Australia	Not scheduled, with no Australian limit. The AIIC listing for ethyl ascorbic acid requires the importer to tell AICIS within 28 days if it will be used above 10%.
Korea	Pre-approved brightening levels are 2% ascorbyl glucoside, 2% ascorbyl tetraisopalmitate (tetrahexyldecyl ascorbate), 3% magnesium ascorbyl phosphate and 1–2% ethyl ascorbyl ether, for lotion, liquid, cream, solid or sheet-mask products reported to MFDS as functional cosmetics.
China	Brightening or spot-fading claims make it a special cosmetic, which needs NMPA registration and a human efficacy test at a designated lab before launch.
Climate	L-ascorbic acid browns faster in heat, so for hot markets and tropical shipping use airless opaque packs, small fills or a heat-stable derivative such as ascorbyl glucoside.

In the lab

Specifications

Typical use level

1–20%0525%

pH window

pH 2.5–72 acid7 neutral10 alkaline

Solubility

Water-solubleOil-soluble

Sensitive to

OxygenWaterLightMetal ions

L-ascorbic acid at 10–20% in low-pH serums; derivatives such as ascorbyl glucoside at 1–5%, and up to 10% in targeted serums.

INCI	Ascorbic Acid; 3-O-Ethyl Ascorbic Acid; Ascorbyl Glucoside; Sodium Ascorbyl Phosphate; Tetrahexyldecyl Ascorbate
Also known as	L-ascorbic acid, Ethyl ascorbic acid, Ascorbyl glucoside, Sodium ascorbyl phosphate, Tetrahexyldecyl ascorbate
Origin	synthetic

Lab notes

Solubility and phase

Water phase for L-ascorbic acid, sodium ascorbyl phosphate, ascorbyl glucoside and ethyl ascorbic acid. Oil phase for tetrahexyldecyl ascorbate.

Stability

Use a low-water or anhydrous base for L-ascorbic acid, with ferulic acid, vitamin E and nitrogen flushing, as it turns yellow then brown in water. Chelate trace iron and copper from water and raw materials. Add derivatives in the cool-down phase.

Regulatory, Australia

Ascorbic acid and the main derivatives are on the AIIC, and some derivative listings carry AICIS information obligations. It is not scheduled and has no EU restriction.

Claims to take care with

'Brightens' and 'helps the appearance of dark spots' are cosmetic. Avoid 'treats melasma' or 'prevents sun damage', as vitamin C is not a sunscreen.