Ingredients

Vitamin C (ascorbic acid)

Vitamin C is used in topical cosmetics in several chemical forms — L-ascorbic acid and its stabilised derivatives — and as a nutrient in food supplements. Stability in formulation is its defining cosmetic-formulation challenge.

At a glance

INCI names

Ascorbic Acid (L-ascorbic acid); Sodium Ascorbyl Phosphate; Magnesium Ascorbyl Phosphate; Ascorbyl Glucoside; Tetrahexyldecyl Ascorbate (lipid-soluble ester); 3-O-Ethyl Ascorbic Acid

Chemical name

L-ascorbic acid: (R)-3,4-dihydroxy-5-((S)-1,2-dihydroxyethyl)furan-2(5H)-one

CAS number

50-81-7 (L-ascorbic acid)

Regulatory class

Cosmetic ingredient (Regulation (EC) No 1223/2009); also nutrient under Directive 2002/46/EC, and an authorised form for vitamin C in food supplements

Cosmetic function

Antioxidant; skin conditioning

What it is

L-ascorbic acid is the natural enantiomer of vitamin C. In cosmetic formulation it is challenging to stabilise: it is hydrophilic, oxidises readily in the presence of water, oxygen and metal ions, and discolours as it oxidises. Cosmetic chemistry has responded by developing a family of derivatives: phosphate esters (sodium and magnesium ascorbyl phosphate), glycoside conjugates (ascorbyl glucoside), lipid-soluble esters (tetrahexyldecyl ascorbate), and ether forms (3-O-ethyl ascorbic acid). Each derivative is, in principle, more stable than the parent acid and is intended to release L-ascorbic acid or an active intermediate after application.

How it is used in parapharmacy products

Vitamin C and its derivatives are used in leave-on facial products marketed for tone-related concerns and as antioxidants intended to support the cosmetic formulation against oxidative degradation and, in marketing claims compliant with Regulation 655/2013, to "help support" the appearance of skin tone. Typical concentrations of L-ascorbic acid in finished products range from a few per cent up to around 15–20% in dedicated formulations; lower concentrations are used for derivatives such as the phosphates and glucosides. The relevant CosIng entries are the operational reference for declared cosmetic functions.

Regulatory status

Neither L-ascorbic acid nor its commonly used cosmetic derivatives are subject to specific concentration restrictions in the Annexes of Regulation (EC) No 1223/2009. As with any cosmetic ingredient, their use is subject to the general safety requirement and to inclusion in the safety assessment for the finished product by the responsible person.

L-ascorbic acid, calcium L-ascorbate and sodium L-ascorbate are authorised as forms of vitamin C in food supplements under Annex II of Directive 2002/46/EC. Authorised health claims for vitamin C, listed in the EU Register of nutrition and health claims, include contributions to a number of bodily functions; the precise wording and conditions of use must be taken from the Register and applied to products that meet the criteria.

Evidence summary

The topical antioxidant effect of L-ascorbic acid in well-formulated, well-preserved vehicles is best characterised as supported by laboratory and human studies, although the magnitude of the in-vivo effect varies with formulation. Effects on diffuse pigmentation and on perceived radiance are documented in clinical reports of higher-concentration formulations. Comparative evidence on the cosmetic equivalence of the various stabilised derivatives is mixed. Claims on cosmetic products must comply with Commission Regulation (EU) No 655/2013 and must not present the product as treating disease.

As a nutrient, oral vitamin C has long-established essential roles in collagen synthesis, antioxidant defence and immune function, and a known role in preventing scurvy at very low intake. Specific health claims permitted on food supplements containing vitamin C are set out in the EU Register.

Safety and known considerations

Topical L-ascorbic acid at higher concentrations can cause stinging or transient erythema in some users, especially in sensitive skin. The acid form is, by definition, low pH (commonly formulated around pH 3.0–3.5 to maximise stability and skin penetration), which is a frequent cause of mild local discomfort. Stabilised derivatives are typically formulated at higher pH and are better tolerated. Oxidation of ascorbic acid in the bottle is signalled by a colour change from clear or pale yellow to orange or brown; once oxidised, the product is no longer cosmetic-grade.

Last reviewed: May 2026.