The Vitamin C 23 Serum — Reddit Reviews
by COSRX
Updated October 17, 2026
23% pure vitamin C fades dark marks fast; oxidation and irritation are real.
What the community says
A high-strength 23% ascorbic acid serum with panthenol, squalane, and sodium hyaluronate, aimed at brightening post-acne marks and dullness. It suits experienced vitamin-C users, but sensitive or tretinoin-treated skin may find it stinging, drying, or barrier-taxing.
What this means for you
What people love
- 23% pure ascorbic acid — serious brightening power
- Dark marks and PIH visibly fade with consistent use
- Noticeable glow with extra hydration
Watch out for
- Stinging, dryness, and barrier damage hit sensitive users
- Breakouts and rough bumps happen for some users
- Sticky, runny texture and an unpleasant smell
Product details
Use caution
Skin Type
Product Traits
Where to buy
What the science says vs. what Reddit says
Hyperpigmentation
Some evidence
Vitamin C: 9 studies tested it on its own. See all 20 studies
On Reddit: PIH starts fading within two months with daily use. 9 mentions
What the studies found
- Most studies found it helped fade dark patches or make skin tone look more even
- For melasma, vitamin C often made patches look lighter
- With microneedling, vitamin C improved melasma in several studies
- It worked about as well as tranexamic acid in some microneedling studies
- Side effects were usually mild, short-lived, or not reported
Studied at 3–30%this product: 23%
Anti-Aging
Some evidence
Vitamin C: 6 studies tested it on its own. See all 17 studies
What the studies found
- All 6 studies that tested vitamin C on its own found it helped with signs of aging
- Studies found it improved wrinkles, including crow’s-feet and lines around the eyes
- It also made sun-damaged skin look smoother and improved overall skin appearance
- It did not seem to improve how much water the skin held more than a placebo
- No side effects were reported in one clinical trial
Studied at 1–30%this product: 23%
Dehydration
Not proven yet
Few or mixed studies. This claim isn't established.
Panthenol: 2 studies tested it on its own. See all 3 studies
Skin Barrier
Not proven yet
Few or mixed studies. This claim isn't established.
Panthenol: 1 study tested it on its own. See all 10 studies
Research context, not treatment advice. Studies are about the ingredient, not necessarily this exact product.
Real Reddit threads — 62 mentions across 25 threads
COSRX The Vitamin C 23 Serum on Reddit, in one place — 25 threads from r/koreanskincare, r/AsianBeauty and 3 more, summarized.
“COSRX Vitamin C 23”
Mentioned
“I forgot what some of the products I've tried but here are some of what I can remember.”
Mentioned
“I've also tried other brands from other countries.”
Mentioned
“it’s a lower concentration and IMO feels more gentle and much less irritating than the 23 version.”
Mentioned
“Which form of vitamin c does cosrx have”
Mentioned
“it has 23% pure vitamin c / L-ascorbic acid”
Mentioned
“Currently popular in my circle: vt reedle shot and pdrn, innisfree retinol, round lab sunscreen, aestura, numbuzin, torriden, cosrx vitamin c 23, mediheal masks, iope retinol, d'alba sunscreen, cell fusion c sunscreen”
Mentioned
“People here don’t touch the following brands much:”
Mentioned
“Why is CosRx not popular?”
Mentioned
“Their new vit-c serum blew up last year”
Mentioned
“all due to the fact they used old IOPE formula”
Mentioned
“I’m hoping here AP will release some of their old premium formulas under Cosrx”
Mentioned
“The vitamin c serum by cosrx. Does an amazing job with brightening!”
Positive
“Oh wow so many great products to choose from but I definitely would grab a bunch of Cosrx”
Positive
“I just bought the Cosrx vit c 13 and I like it so far.”
Positive
“Cosrx vitamin c 23. I used it twice a day for about 4 months and I saw results in the first week.”
Positive
“Agree with CosRx Vit C.”
Positive
“it did brighten my skin well.”
Positive
Dupes & Alternatives
Anua
Azelaic Acid Hyaluron Redness Soothing Serum
Better for Hyperpigmentation
9 shared traits
713 mentions
