COSRX Vitamin C 23 vs. numbuzin No.5+
Maximum-strength 23% pure ascorbic acid against an eight-active, glutathione-forward clinical blend with no pure ascorbic acid at all.
Criteria | COSRX The Vitamin C 23 Serum | numbuzin No.5+ Glutathione Vitamin Concentrated Serum |
|---|---|---|
| Price | $25.00 | $25.00 |
| Price / unit | $1.25/mL | $0.83/mL |
| Size | 20 mL | 30 mL |
| Price checked | 9/12/2026 | 9/12/2026 |
Both are fragrance-free brightening serums at the same $25 sticker price, but COSRX pushes pure vitamin C concentration to the maximum while numbuzin skips pure ascorbic acid entirely in favor of a broader active blend.
Why compare these two specifically
Same sticker price, both fragrance-free, but opposite strategies: maximum single-active potency versus a broader multi-active blend built around glutathione and tranexamic acid instead of pure ascorbic acid.
Price per milliliter
COSRX runs $1.25 per milliliter ($25.00 for 20mL). numbuzin runs $0.83 per milliliter ($25.00 for 30mL). Same sticker price, but numbuzin's larger bottle makes it meaningfully cheaper per mL.
Maximum potency vs. broad multi-active blend
COSRX layers 23% pure L-ascorbic acid with a stable derivative, niacinamide, squalane, adenosine, and glutathione, maximum-strength vitamin C as the clear headline. numbuzin skips pure ascorbic acid entirely, building around niacinamide at 5%, tranexamic acid at 4%, arbutin, a stable vitamin C derivative, ceramide NP, bisabolol, and glutathione, eight ingredients working together rather than one dominant active.
Our take
If maximum vitamin C potency is specifically what you want, and you're experienced with actives, COSRX delivers that directly, at a real premium per mL. If you'd rather have a broader, gentler multi-active approach with real barrier support built in, and a lower per-mL cost, numbuzin covers more ground without pure ascorbic acid's irritation risk.
COSRX The Vitamin C 23 Serum: $1.25/mL. Maximum-strength 23% pure L-ascorbic acid, for experienced actives users specifically.
numbuzin No.5+ Glutathione Vitamin Concentrated Serum: $0.83/mL. An eight-active blend built around tranexamic acid and glutathione instead of pure ascorbic acid, at a lower per-mL cost.
See our full best Korean serums by concern guide, or browse the rest of our serum coverage.
Shop these picks
Affiliate links: we may earn a commission at no extra cost to you.
Price checked 9/12/2026
Price checked 9/12/2026
Related comparisons
Frequently asked
Which is stronger, COSRX Vitamin C 23 or numbuzin No.5+?
COSRX, with pure L-ascorbic acid at a maximum 23% concentration. numbuzin uses no pure ascorbic acid at all, relying instead on a broader eight-active blend built around niacinamide, tranexamic acid, and glutathione.
Which is cheaper per milliliter, COSRX Vitamin C 23 or numbuzin No.5+?
numbuzin, at $0.83 per milliliter versus COSRX's $1.25 per milliliter, despite both carrying the same $25 sticker price.
Are COSRX Vitamin C 23 and numbuzin No.5+ fragrance-free?
Yes, both are confirmed fragrance-free.