Vitamin C

Skin Renewing Vitamin C Serum

CeraVe

A-OXitive Antioxidant Defense Serum

Avene

C E Ferulic

SkinCeuticals

Good RCT evidence for photoageing, brightening, and post-inflammatory hyperpigmentation. Evidence is strongest for LAA at 10% to 20% in low-pH formulations. Derivative forms have less robust human data.

Very well tolerated. Stinging at application is common at low pH. Rare allergic or contact reactions. No photosensitisation (can be used in the morning). Oxidised product (yellow-orange discolouration) may cause temporary staining and reduced efficacy but is not dangerous.

No systemic concerns at topical doses. Vitamin C is a water-soluble vitamin; excess does not accumulate in tissue. Decades of use without safety signals. One of the most universally safe actives in the formulator's toolkit.

A strong evidence-based antioxidant for morning use. Particularly valuable paired with sunscreen, as it provides complementary photoprotection. Most appropriate for brightening goals and general photoageing prevention.

“All vitamin C serums are the same.”

The form matters enormously. L-ascorbic acid has the best evidence but is unstable. Derivatives like ascorbyl glucoside are stable but may not convert to active LAA at meaningful concentrations in skin. A product labelled "vitamin C" could contain any of a dozen forms with very different efficacy profiles.

“If your vitamin C serum turns orange or yellow it has gone bad and will harm you.”

Oxidised vitamin C (dehydroascorbic acid) loses its antioxidant benefit and may slightly stain skin temporarily. It is not harmful. However, a fully oxidised serum provides no active benefit, so fresh product in stable packaging is worth prioritising.

“Vitamin C and niacinamide cancel each other out.”

This is based on outdated chemistry: the concern was that they combine to form nicotinic acid (niacin flush). At cosmetic concentrations, room temperature, and typical skin pH, this reaction is negligible. Multiple modern formulations combine both with no clinical evidence of interaction at consumer-use concentrations.