RRevelika
antioxidant

Vitamin C

INCI · Ascorbic Acid · also L-Ascorbic Acid, Vitamin C

EWG safety

How it works

Ascorbic acid is a potent antioxidant that neutralizes reactive oxygen species generated by UV and pollution exposure before they degrade collagen. It's also a required cofactor for the enzymes that stabilize collagen's triple helix, and it inhibits tyrosinase, the enzyme driving melanin production — which is why it both brightens and firms.

The catch is stability: L-ascorbic acid oxidizes readily on contact with light, air, and water, turning yellow-brown and losing potency, which is why formulation matters as much as concentration. This is the single biggest reason patients tell me their vitamin C serum "stopped working" — it didn't stop working, it oxidized in the bottle.

The evidence

The landmark Pinnell-era research on combining 15% L-ascorbic acid with vitamin E and ferulic acid demonstrated significantly enhanced photoprotection and antioxidant stability compared to vitamin C alone — this combination remains the benchmark formulation in the field. Subsequent studies on standalone ascorbic acid have also documented improvements in fine lines and photodamage with sustained daily use over several months.

Suitability

  • Dull, uneven-toned skin: the most reliable brightening antioxidant available
  • Photoaging concerns: supports collagen synthesis and UV-damage defense
  • Sensitive skin: consider derivatives like sodium ascorbyl phosphate for a gentler option
  • Oily and acne-prone skin: generally well tolerated alongside oil-control actives

Concentration

8–15% is the clinical sweet spot; I rarely recommend going above 20%, where irritation rises without added benefit. Look for an opaque, airtight bottle — a vitamin C serum that's turned dark yellow has already oxidized and should be replaced regardless of how much product is left.

Conflicts & combinations

  • Pairs synergistically with vitamin E (tocopherol) and ferulic acid for stability and enhanced antioxidant protection
  • Layering with retinol in the same session can destabilize both and increase irritation — many derms recommend separating AM/PM
  • Avoid direct layering with benzoyl peroxide, which can oxidize ascorbic acid
  • Best applied on clean, dry skin before heavier creams and sunscreen
Suitability
Suits skin type
dry oily combo sensitive acne prone mature normal
Targets
  • hyperpigmentation
  • dullness
  • anti aging
Use caution with
  • redness
Concentration
Concentration0 – 20%
Effective from
10%
Max safe
20%
Frequently asked
What's the best percentage of vitamin C for skin?

Most clinical benefit is seen between 8% and 15% L-ascorbic acid; higher concentrations increase irritation risk without proportional benefit.

Why did my vitamin C serum turn orange?

That's oxidation — L-ascorbic acid degrades on exposure to light and air and loses its effectiveness once it changes color.

Can I use vitamin C and niacinamide together?

Yes, in modern stabilized formulations this pairing is well tolerated and common.

Should vitamin C be used in the morning or at night?

Morning is preferred, since it boosts protection against daytime UV and pollution exposure, ideally under sunscreen.

Is vitamin C safe during pregnancy?

Yes, topical ascorbic acid is considered safe during pregnancy.

The evidence