The Vitamin C 13 Serum — Reddit Reviews
by COSRX
Updated October 3, 2026
13% vitamin C serum for dark spots and faster morning layering; fridge helps.
What the community says
A 13% ascorbic acid serum with panthenol, sodium hyaluronate, glutathione, and licorice root extract. People use it for dark spots and morning routines, but the dropper bottle oxidizes easily, so fridge storage helps.
What this means for you
Backed by 9 threads from r/koreanskincare, r/30PlusSkinCare and 1 more.
Read the threads ↓What people love
- 13% vitamin C for dark spots
- Less sticky than many vitamin C serums
- Plays nice with sensitive, rosacea-prone skin
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
- In melasma studies, vitamin C on the skin often made patches look lighter over time
- Used with other treatments, vitamin C sometimes faded melasma more than the other treatment alone
- For sun spots, vitamin C showed some fading, but one study had mixed results
- It worked about as well as glycolic acid for fading melasma patches in one large review
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 — 11 mentions across 9 threads
COSRX The Vitamin C 13 Serum on Reddit, in one place — 9 threads from r/koreanskincare, r/30PlusSkinCare and 1 more, summarized.
“you could try COSRX vitamin C 13 to start, it’s a lower concentration and IMO feels more gentle and much less irritating than the 23 version.”
Mentioned
“Cosrx vitamin c is the only product that my skin had a bad reaction to 😩”
Mentioned
“the vitamin c gave me a dermatitis-like rash.”
Mentioned
“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
“I like the COSRX vitamin c 13 serum.”
Mentioned
“There’s also a 23% version available.”
Mentioned
“COSRX 23% is incredible”
Mentioned
“I keep my COSRX Vitamin C 13 serum in the fridge and it oxidizes very slowly.”
Positive
“It doesn't cause me to break out either”
Positive
“it's not very sticky compared to other vitamin c products I've tried.”
Positive
