The Vitamin C 23 Serum — Reddit Reviews
by COSRX
Updated September 23, 2026
23% L-ascorbic acid for serious brightening; stings sensitive skin.
What the community says
A high-strength vitamin C serum built for fading PIH, dullness, and old acne marks. It can give fast glow and good hydration, but the 23% punch makes stinging, dryness, and oxidation complaints very real.
What this means for you
What people love
Watch out for
Product details
Use caution
Skin Type
Product Traits
Key Ingredients
Where to buy
What the science says vs. what Reddit says
Hyperpigmentation
Some evidence
Vitamin C: 7 studies tested it on its own. See all 24 studies
On Reddit: High 23% Vitamin C concentration targets dark spots but stings sensitive skin and smells off at times. 8 mentions
What the studies found
- Most studies found vitamin C helped fade dark spots or patches
- Most studies in melasma found it made patches look lighter over time
- It worked about as well as glycolic acid in one study
- One study found only weak fading, and one dark-spot measure did not beat a placebo
Studied at 0.2–30%this product: 23%
Research context, not treatment advice. Studies are about the ingredient, not necessarily this exact product.
Real Reddit threads — 61 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
“Cosrx vitamin c is the only product that my skin had a bad reaction to 😩”
Cautionary
“the vitamin c gave me a dermatitis-like rash.”
Cautionary
“it has 23% pure vitamin c / L-ascorbic acid”
Cautionary
“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.”
Positive
“I used it twice a day for about 4 months and I saw results in the first week.”
Positive
“Agree with CosRx Vit C... it did brighten my skin well.”
Positive
Dupes & Alternatives
Anua
Azelaic Acid Hyaluron Redness Soothing Serum
Better for Hyperpigmentation
7 shared traits
676 mentions
