L-Ascorbic Acid (Vitamin C)
Water-soluble antioxidant that inhibits tyrosinase and stimulates collagen synthesis. Unstable upon oxidation, requiring careful storage.
Evidence by route
Topical application
Clinical trials confirm efficacy for melasma, photoaging, and photoprotection. Synergy with vitamin E and ferulic acid enhances photoprotective properties. Evidence base is limited by difficulties in standardizing formulation stability.
- Pullar JM et al. Nutrients. 2017;9(8):866. PMID 28805671
- Murray JC et al. J Am Acad Dermatol. 2008;58(3):418-424. PMID 18603326
How to read tiers A–F
- BLimited evidence. One RCT or several controlled studies with limitations
Tolerability and safety
- Working concentrations
- 10–20% (optimal pH 2.5–3.5)
- Irritation potential
- Medium
- Allergen risk
- Low
- Pregnancy
- Safe
- Suitable for
- Normal, Combination, Oily
- Use with caution
- Sensitive, Dry
For sensitive skin
Concentrations above 15% may cause stinging and redness on sensitive skin. Starting at 10% is recommended.
Combinations with other ingredients
Works well with
Ferulic Acid
Ferulic acid stabilizes vitamin C and doubles the formula's photoprotective properties. They work as a single antioxidant network.
Glycolic Acid
Applying vitamin C over AHA boosts bioavailability of both – low pH helps ascorbic acid stability. Best done in the morning.
Tocopherol (Vitamin E)
Classic pair: vitamin E stabilizes ascorbic acid and enhances photoprotection. Lin 2003 showed 4-fold UVB protection boost when combined.
Niacinamide
The old incompatibility myth is debunked. In modern formulas these ingredients work together, enhancing brightening and antioxidant effects.
Does not combine with
Copper Peptides (GHK-Cu)
Vitamin C reduces copper in GHK-Cu, breaking the peptide. Use at different times: C in morning, copper peptides in evening.
Benzoyl Peroxide
BPO oxidizes ascorbic acid, inactivating it. Use at different times of day.
Tretinoin
Tretinoin is already irritating, and L-AA at acidic pH adds stinging and dryness. Tretinoin also oxidizes in acidic media. Dermatologists recommend spacing them: C in the morning under SPF, tretinoin at night on dry skin.
Hydroxypinacolone Retinoate
HPR (hydroxypinacolone retinoate) activates at neutral pH and needs a stable environment. Acidic L-AA reduces HPR bioavailability. Better to space them out or use a stable C form.
Retinaldehyde
Same issue as with retinol: L-AA needs acidic pH (3–3.5), retinal needs neutral. In one layer it oxidizes faster and may amplify stinging. Standard advice – C in the morning, retinal at night.
Retinol
Different optimal pH: retinoids need neutral, vitamin C needs acidic. Use at different times: C in morning, retinol at night.
About this ingredient
L-Ascorbic Acid (vitamin C) is a water-soluble antioxidant, one of the most studied actives in dermatology. The natural form of vitamin C, not synthesized in the human body (loss of gulonolactone oxidase ~60 million years ago) and must come from food. Mechanism. Neutralizes free radicals (ROS) after UV exposure, regenerates oxidized vitamin E, cofactor of proline and lysine hydroxylases – without vitamin C collagen I and III synthesis stalls. Inhibits tyrosinase and reduces melanin synthesis. Lowers expression of matrix metalloproteinases (MMP-1). Where applied. Antioxidant serums, anti-aging creams, depigmenting agents, photoprotective formulas (5–20%). Effective at 10–20% with pH 2.0-3.5. In Spain – SkinCeuticals CE Ferulic (gold standard), Sesderma C-Vit, Endocare Radiance C, La Roche-Posay Pure Vitamin C, Martiderm Vitamin C. Evidence base. Pinnell 2001 (RCT in 10 patients, 12 weeks) – protection from UVB-induced erythema and pigmentation with 10% L-ascorbic acid. Burke 2005 – improved photoaging, reduced wrinkle depth. Espinal-Perez 2004 – depigmenting effect in melasma. Lin 2005 – vitamin C combined with vitamin E and ferulic acid doubles photoprotection. Controversy and stability. L-ascorbic acid is unstable – oxidizes in light and air to dehydroascorbic acid, then to erythrulose (causes yellowing). Stable only at pH <3.5 in aqueous formulas, more stable in anhydrous formulas (silicone, oil). Requires dark packaging and rapid use after opening. Safety. CIR rated L-ascorbic acid safe at cosmetic concentrations (2005, re-evaluated 2018). Irritation possible from low pH in sensitive skin – stinging and erythema in the first days. Often cross-reactive with tretinoin and AHAs, requires gradual introduction. Pregnancy and lactation – safe topically. Suitable for all skin types. On sensitive skin – start at lower concentration (5–10%) or prefer stable derivatives (ethyl ascorbic acid, MAP, SAP).
Frequently asked questions
Is L-Ascorbic Acid (Vitamin C) safe during pregnancy?
L-Ascorbic Acid (Vitamin C) is considered safe during pregnancy at typical cosmetic concentrations. Systemic absorption through the skin is minimal.
What skin types is L-Ascorbic Acid (Vitamin C) for?
L-Ascorbic Acid (Vitamin C) suits: normal, combination, oily. Use with caution in: sensitive, dry.
Can L-Ascorbic Acid (Vitamin C) irritate the skin?
L-Ascorbic Acid (Vitamin C) has moderate irritation potential. Sensitive skin may show a transient reaction that usually settles with adaptation.
What is L-Ascorbic Acid (Vitamin C) and what does it do in cosmetics?
Water-soluble antioxidant that inhibits tyrosinase and stimulates collagen synthesis.
What's the INCI name for L-Ascorbic Acid (Vitamin C)?
The INCI name is Ascorbic Acid. It may also appear as: Vitamin C, L-Ascorbic Acid.
What concentration of L-Ascorbic Acid (Vitamin C) is effective?
10–20% (optimal pH 2.5–3.5)
See L-Ascorbic Acid (Vitamin C) in a product composition right on the store page
The Evigrade extension adds an evidence panel to iHerb, Sephora, Druni and 12 more stores. This ingredient and every other one in the product show evidence-tier, allergen risk and pregnancy/lactation flags at a glance.
Similar in action
Explore by category
Ingredients in the same category
Licorice Root Extract, Lilium Candidum Bulb Extract, Magnesium Ascorbyl Phosphate, Malic Acid, Nonapeptide-1, Sodium Ascorbyl Phosphate, Ascorbyl Glucoside, Diacetyl Boldine
Related articles
Published: · updated: