What it does
- Provides antioxidant defence against environmental and UV-induced free radicals.
- Supports a brighter, more even-looking complexion.
- Widely documented to support collagen-related skin health.
How it works
L-ascorbic acid is the most studied, biologically active form but is unstable and needs a low pH (below about 3.5) to penetrate, which can be irritating. Derivatives such as 3-O-ethyl ascorbic acid, sodium ascorbyl phosphate (SAP) and magnesium ascorbyl phosphate (MAP) trade some potency for much better stability and gentler pH, converting to ascorbic acid in the skin.
Use level
- Typical use level
- L-AA 5–20%; derivatives ~1–5%
L-ascorbic acid is commonly used at 5–20% (10–15% typical). Stable derivatives are generally used at about 1–5% depending on the specific ingredient. 3-O-ethyl ascorbic acid is a common stable, water-soluble option.
Formulation considerations
- L-AA: needs low pH (below ~3.5), and is highly prone to oxidation; use antioxidants, chelators, low water activity or anhydrous systems and airless opaque packaging.
- Derivatives: more stable and effective at higher, gentler pH (often around 5–7).
- Discolouration (yellowing) signals oxidation of L-AA.
What it pairs with & what to avoid
Pairs well with
- Vitamin E and ferulic acid (classic antioxidant network)
- Niacinamide (compatible at normal pH)
- Sunscreen (daytime antioxidant support)
Use with care / avoid
- High pH for free L-AA (loses activity)
- Prolonged air/light exposure without stabilisation
Regulatory status
Ascorbic acid and its common cosmetic derivatives are listed in the EU CosIng database and are long-established cosmetic ingredients.
Common questions
What percentage of vitamin C should I use?
L-ascorbic acid is commonly 10–15% (range 5–20%). Stable derivatives are typically used at about 1–5%.
Which vitamin C is best — ascorbic acid or a derivative?
L-ascorbic acid is the most potent but least stable and needs low pH. Derivatives such as 3-O-ethyl ascorbic acid are more stable and gentler; the best choice depends on the product and skin type.
Can I use vitamin C with niacinamide?
Yes. At normal formulation pH they work together; the old warning came from outdated, impure high-heat conditions.
Why did my vitamin C serum turn yellow or brown?
That is oxidation of L-ascorbic acid. Proper pH, antioxidants, chelation and airless opaque packaging slow it down.