The Vitamin C 13 Serum — Reddit Reviews
by COSRX
Updated September 22, 2026
13% vitamin C serum that brightens and fades dark spots; gentler starter pick.
What the community says
A 13% ascorbic acid serum with added vitamin C derivatives, panthenol, and squalane. People reach for it as a gentler starter and morning layer for dark spots and glow. Refrigerate it; oxidation is the annoying catch.
What this means for you
What people love
- 13% vitamin C starter serum
- Brightens dark spots and dull skin
- Less sticky, absorbs fast
Watch out for
Product details
Skin type data limited
Where to buy
What the science says
Hyperpigmentation
Some evidence
Vitamin C: 7 studies tested it on its own. See all 24 studies
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: 13%
Research context, not treatment advice. Studies are about the ingredient, not necessarily this exact product.
Real Reddit threads — 9 mentions across 8 threads
COSRX The Vitamin C 13 Serum on Reddit, in one place — 8 threads from r/koreanskincare, r/AsianBeauty and 2 more, summarized.
“you could try COSRX vitamin C 13 to start”
Mentioned
“it’s a lower concentration”
Mentioned
“feels more gentle and much less irritating than the 23 version.”
Mentioned
“right now, I'm planning on getting ... cosrx vitamin c 13”
Positive
“Agree with CosRx Vit C... it did brighten my skin well.”
Positive
“Cosrx vitamin c 23.”
Positive
“I decided to try the Cosrx Vitamin C serums. I started out with the 13 one and apply it in the morning under moisturizer and sunscreen.”
Positive
“There has been zero irritation from the serum, the only small con is that it smells like meat broth.”
Positive
“I’ve finished one bottle of Vitamin C 13 so far.”
Positive
“I've used COSRX for a while (daily for about 2 years) both C13 and C23.”
Positive
“Loved that it was effective with dark spots, absorbed quickly, and cost effective.”
Positive
“I have sensitive, rosacea prone skin... and nothing but Cosrx worked like wonder.”
Positive
“You can try out vitamin C serum that has low concentration like cosrx vitamin c13 one!”
Mentioned
“You need to keep vitamin serum in fridge cause it's easy to oxidize”
Mentioned
“try to finish it within 2 months.”
Mentioned
