Vitamin C
Vitamin C is one of the most studied and evidence-supported brightening and antioxidant ingredients in skincare. It exists in multiple forms in skincare formulations, ranging from the highly potent but unstable L-ascorbic acid to more stable derivatives developed specifically to overcome the challenges of topical vitamin C use. Korean skincare has been particularly innovative in adopting stable derivatives that suit sensitive and reactive skin.
General Information Only. This page provides educational skincare information and is not medical advice. If you have persistent acne, eczema, rosacea, allergies, skin irritation, pigmentation changes or any medical skin condition, please consult a qualified dermatologist or healthcare professional before changing your skincare routine. Individual results vary. Always patch test new products.
Forms of vitamin C in skincare
L-ascorbic acid
The most biologically active form. Works at pH below 3.5. Highly effective but oxidises quickly (turns yellow/orange), can irritate sensitive skin. Most-researched with the strongest evidence base.
Ethyl ascorbic acid (3-O-ethyl ascorbic acid)
Stable derivative very popular in Korean skincare. Works across a broader pH range, suitable for more skin types, penetrates well and converts to ascorbic acid in skin.
Ascorbyl glucoside
Stable, water-soluble. A gentler option that converts to ascorbic acid in skin. Good for sensitive skin. Slightly less potent than L-ascorbic acid but much easier to formulate with.
Sodium ascorbyl phosphate
Very stable, water-soluble, well-tolerated by sensitive skin. Often used in formulations for acne-prone and reactive skin due to its gentleness.
Tetrahexyldecyl ascorbate
Oil-soluble, highly stable, high skin penetration. Used in richer formulations and may be particularly suitable for dry and mature skin.
What vitamin C does
Antioxidant protection
Vitamin C neutralises free radicals generated by UV exposure and pollution, reducing oxidative damage to skin cells. Most effective in the morning alongside SPF.
Brightening
Inhibits tyrosinase, reducing melanin production. Over 8–12 weeks of consistent use, may visibly reduce dark spots, post-acne marks and general dullness.
Supports collagen synthesis
Ascorbic acid is a cofactor for enzymes involved in collagen formation. Regular use may support the skin's collagen-maintaining processes, though topical effects are modest.
Complementing SPF
SPF filters UV light; vitamin C handles the oxidative stress from UV that does get through. Together they provide more comprehensive protection than SPF alone.
The Korean approach to vitamin C
Korean skincare formulations tend to favour stable vitamin C derivatives over high-concentration L-ascorbic acid. This reflects the broader Korean skincare philosophy of gentle, consistent, long-term skin maintenance rather than aggressive treatment. Products using ethyl ascorbic acid, ascorbyl glucoside or sodium ascorbyl phosphate are more easily layered into a multi-step routine without the pH management challenges of L-ascorbic acid — and are better suited to sensitive skin types that make up a large proportion of the Korean skincare market.
Note on vitamin C and niacinamide
A historical concern existed that mixing niacinamide and vitamin C could form niacin (causing a flush) and reduce the efficacy of vitamin C. Modern research suggests this is not a significant concern at concentrations used in typical skincare and at skin temperature. However, as a practical approach, spacing them (vitamin C in the morning, niacinamide in the evening, or applying one then waiting before the other) is a simple way to avoid any potential interaction without the need for strict separation.