COSRX
The Vitamin C 13 Serum
The everyday vitamin C serum in COSRX's line, for a brighter, more even look. 20 ml, worn after toner and before sunscreen.
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- Suited to
- SensitiveCompromised barrierUneven toneDull
- Helps with
- Barrier weaknessEarly environmental damageUneven tone and dullnessExcess oil
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- 30-day returns
- Free US shipping on orders of $100 or more
- Dispatched within 2 business days
How it works
This is the vitamin C step that goes into a morning routine and stays there. It belongs after toner and before moisturizer and sunscreen, on skin that is dry rather than wet. What changes is tone rather than texture: a brighter, more even look that shows after a few weeks of consistent mornings. Sunscreen over the top is the other half of the habit, and a morning routine that includes this step should not skip it. It suits someone who wants one active step in the morning and keeps the evening free for an exfoliant or a retinoid.
Key benefits
- Ascorbic acid is declared at 13%, matching the name.
- Ethyl Ascorbic Acid is another, more stable vitamin C form on the list.
- Caffeine and sodium hyaluronate sit in the top ten of the list.
- Niacinamide, glutathione and licorice root extract round out the formula.
Key actives
Ascorbic Acid
declared at 13%, the direct vitamin C form in the name
Ethyl Ascorbic Acid
a stable, additional vitamin C form on the list
Niacinamide
supports a clearer, more even look
Caffeine
an antioxidant that also brightens the look of the eye area
COSRX The Vitamin C 13 Serum
What makes this a 13% vitamin C serum rather than a lower-strength brightening product?
Ascorbic acid appears second on the ingredient list, directly after water, declared at 13%, which is the number in the product name. A second, more stable vitamin C form, 3-O-ethyl ascorbic acid, follows a few entries later, and caffeine and sodium hyaluronate sit in the upper half of the list as well. That combination places this in the direct-acid category of vitamin C serums rather than a milder derivative-only formula.
Will a 20 ml bottle of 13% vitamin C be too intense for my skin?
Direct ascorbic acid at this strength can sting or feel warm on skin that has not used it before, so easing in with alternate nights rather than daily use from the start is sensible. The list carries no fragrance, essential oil, denatured alcohol, silicone, paraben, or added colourant, removing several common irritant categories. Panthenol and allantoin sit mid-list as calming ingredients, though anyone with compromised or actively reactive skin should patch test before applying it broadly.
Does this serum need weeks of use before tone improves?
Ascorbic acid, glutathione, and tocopherol work together as an antioxidant routine that builds over repeated daily applications rather than producing a change overnight. Niacinamide, positioned near the end of the list, adds a further ingredient associated with a more even-looking complexion over time. Applying it every morning for several weeks is the realistic window for judging whether tone and texture have shifted.
Should this go on before or after my other morning serums?
This vitamin C serum is generally applied early in a morning routine, after toner and before heavier creams or sunscreen, since ascorbic acid performs its antioxidant role best close to the skin. Nothing on this ingredient list is known to conflict with a mineral or chemical sunscreen used afterward. Avoid layering it in the same session as a separate strong exfoliating acid, since stacking two direct acids at once raises the chance of irritation.
How do I check that this 20 ml bottle is the real Korean-market formula?
This product's own barcode, 8800311121911, is a genuine EAN specific to this bottle, so matching that number against your box is a useful first check. COSRX also runs its own verification: the batch number and expiration date on your unit are entered on the checking page at cosrx.com, read directly off the packaging rather than from any listing. Using both the barcode and the batch check together is the most reliable way to confirm what you have is authentic.
- Ships from
- California
Duties are prepaid. Nothing is owed at delivery. Returns are accepted for 30 days, by mail.
Orders ship from our California warehouse, dispatched within 2 business days, and arrive in 3 to 5 days. Shipping is free on orders of $100 or more.
We split shipments free, so one out-of-stock item never holds up the rest of your order.
Where this unit came from
- 1Seoul
Bought as Korean-market stock - 2Customs
Duty paid by us before it enters the US - 3California
Ships domestically, no international leg
We stock the version of a formula that is sold in Korea, not the release a brand prepares for another market under the same name.
Every unit keeps its original barcode and batch code intact, so the unit in your hands can be checked against the brand’s own records.
Import duties are paid by us before the parcel reaches you, so nothing is owed at the door, and returns run for 30 days.
Every claim on this page traces to the unit in the box, the barcode, the batch code and the price you can read for yourself.
Payment and security
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How to use
- Use the Vitamin C 13 Serum in the morning, after toner and before moisturizer, on skin that has dried off rather than damp skin.
- Three or four drops covers the whole face and neck. Press it in and let it settle for a minute.
- Toner first, this second, then moisturizer, then sunscreen as the last step of the morning.
- Once a day, in the morning. Do not stack it in the same routine as an exfoliating acid or a retinoid; give those the evening instead.
Reviews
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COSRX, Korean-market original
Vitamin C 13% Serum, 20 ml, with Niacinamide.
Verify your unit when it arrives
Verify your unit when it arrives
Korean-market stock with the original barcode and batch code intact, exactly as it left Korea.
COSRX verifies units itself. Find the verification page on cosrx.com and enter the batch number and expiration date printed on your unit. Read them off the package rather than from us, which is the point.
Source: COSRX FAQ
On the unit itself
- The Korean-market barcode, unaltered from the retail package.
- The manufacturer’s batch code, exactly as the maker printed it.
정품Genuine article, Korean-market stock
What professionals say
What professionals say
What skin-care professionals say about the key actives in this formula, quoted from the medical sources linked beside each.
Using topical vitamin C can result in less cell damage and better-looking skin.
Melissa Piliang, MDDermatologist, Cleveland Clinic It has also been proven that caffeine stimulates lipolysis, which Lupo et al postulated may contribute to improvements in lower eyelid sagging and puffiness.
Stacey J. PilkingtonDO, Azeal Dermatology Institute, The Journal of Clinical and Aesthetic Dermatology
1 more professional perspective
Niacinamide helps reduce the appearance of pores in a few ways. By strengthening the skin barrier and improving elasticity, pores appear less noticeable and more even.
Ashlyn YankeAesthetician, Cleveland Clinic
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