Vitamin C Serums: How to Choose the Right One for Your Skin
Vitamin C is one of the most researched skincare ingredients in existence. It brightens, protects, stimulates collagen and fades pigmentation. But walk into any pharmacy and you're confronted with dozens of vitamin C serums at wildly different price points — and most of them don't work.
Here's what an Independent Nurse Prescriber actually looks for in a vitamin C serum.
Why vitamin C is worth using
L-ascorbic acid (the active form of vitamin C) does several things simultaneously:
- Antioxidant protection — neutralises free radicals from UV and pollution
- Brightening — inhibits melanin production, fading dark spots and hyperpigmentation
- Collagen synthesis — vitamin C is essential for collagen production; using it topically supports skin structure
- SPF enhancement — vitamin C + SPF together outperform either alone
The problem with most vitamin C serums
L-ascorbic acid is notoriously unstable. It oxidises rapidly when exposed to air and light, turning yellow then brown — at which point it's largely inactive. Cheap serums often contain low concentrations, poor packaging, or already-oxidised vitamin C.
Effective vitamin C serums require:
- Correct pH (below 3.5 for L-ascorbic acid to be absorbed)
- Concentration of 10–20% (below 10% is largely ineffective)
- Stable packaging (dark glass, air-limiting dispenser)
- Or a stable derivative (tetrahexyldecyl ascorbate, ascorbyl glucoside)
L-ascorbic acid vs vitamin C derivatives
L-ascorbic acid (LAA) is the gold standard — most potent, most researched, but most unstable and potentially irritating. Best for oily or normal skin.
Tetrahexyldecyl ascorbate (THD ascorbate) — oil-soluble, highly stable, converts to L-ascorbic acid in skin. Less irritating, better for dry or sensitive skin. Used in Medik8's C-Tetra range.
Ascorbyl glucoside — gentler, water-soluble derivative. Lower potency but good for those who can't tolerate LAA.
Which vitamin C products does Stratum Clinic recommend?
For high potency — Obagi Professional-C Serum
Available in 10%, 15% and 20% L-ascorbic acid. Pharmaceutical-grade formulation at the correct pH. The 15% is the sweet spot for most people — effective without unnecessary irritation. Used in professional aesthetic practice for decades.
For sensitive or dry skin — Medik8 C-Tetra
Uses THD ascorbate — stable, well-tolerated, and highly effective. The Luxe version adds vitamin E and ferulic acid for enhanced antioxidant activity. A strong everyday vitamin C for those who find LAA too harsh.
For daily-use moisturiser with vitamin C — Medik8 Daily Radiance Vitamin C
Combines vitamin C with hydration in a lightweight daily moisturiser. Convenient for those who want antioxidant protection without a separate serum step.
How to use vitamin C correctly
- Apply every morning, after cleansing, before SPF
- Start with lower concentrations if new to vitamin C (10%, then increase)
- Store in a cool, dark place — not a sunny bathroom shelf
- Discard if it turns brown/orange — it's oxidised and inactive
- Don't use with niacinamide in the same step (reduces efficacy)
Related Reading
- How to Get Rid of Pigmentation — A Clinician's Guide
- Retinol vs cosmeceutical retinoid: Which Is Right For You? — combining vitamin C with retinoids
- Best Skincare Routine for Rosacea — vitamin C options for sensitive skin
Questions about which vitamin C is right for your skin? Book a free written skin assessment with our Independent Nurse Prescriber.