The Vitamin C 13 Serum — Reddit Reviews
by COSRX
Updated October 16, 2026
13% ascorbic acid fades dark spots quickly with a low-sticky finish; oxidation-prone.
What the community says
A 13% ascorbic acid serum aimed at dark spots, with panthenol and allantoin in the formula. Sensitive, rosacea-prone users may find it comfortable, though one report describes a dermatitis-like rash and oxidation demands refrigeration and quick use.
What this means for you
Backed by 9 threads from r/koreanskincare, r/30PlusSkinCare and 1 more.
Read the threads ↓What people love
- 13% ascorbic acid for dark spots
- Quick-absorbing, low-sticky texture
- Worked without breakouts for sensitive, rosacea-prone skin
Watch out for
- Dropper packaging and pH 3.5–4.0 accelerate oxidation
- Triggered a dermatitis-like rash for one user
Product details
Product Traits
Key Ingredients
Skin type data limited
Where to buy
What the science says
Hyperpigmentation
Some evidence
Vitamin C: 9 studies tested it on its own. See all 20 studies
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: 13%
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: 13%
Research context, not treatment advice. Studies are about the ingredient, not necessarily this exact product.
Real Reddit threads — 12 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
