The Vitamin C 13 Serum (Single)
The everyday vitamin C serum in COSRX's line, for a brighter, more even look, worn after toner and before sunscreen.
No reviews yet- Korean-market formula
- Ships from California or direct from Korea
- Korean barcode and batch code intact
- 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
- Tracked delivery to your door
Key benefits
- Ascorbic acid is declared at 13%, matching the name.
- Another, more stable vitamin C derivative sits just below it 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
Inside the formula
Inside the formula
- 2Ascorbic Acid
- 9Caffeine
- 23Niacinamide
Where each key active sits on the declared ingredient list, by entry number. Position is proportion: the further forward, the larger its share.
COSRX The Vitamin C 13 Serum (Single)
Is this single bottle the same formula as COSRX's other Vitamin C 13 packs?
The ingredient list here matches the direct-acid vitamin C formula COSRX sells across its Vitamin C 13 line: ascorbic acid declared at 13%, second after water, with 3-O-ethyl ascorbic acid as a second, more stable form a few entries later. Caffeine and sodium hyaluronate sit in the upper half of the list as well. Whether it is sold as a single bottle or a multipack, the same 13% ascorbic acid formula is what is inside.
Can I use this if I have sensitive skin that reacts to strong actives?
A direct ascorbic acid serum at this declared strength can feel warm or tingly on skin unused to vitamin C, so introducing it a few nights a week before daily use is a sensible approach. No fragrance, essential oil, denatured alcohol, silicone, paraben, or added colourant appear on the list, which removes several common irritants. Panthenol and allantoin offer some calming support mid-list, but patch testing first is still worthwhile for reactive skin.
When should I expect to see brighter, more even skin from daily use?
Ascorbic acid, glutathione, and tocopherol form an antioxidant combination that works with sustained daily use rather than a single application. Niacinamide, positioned toward the end of the list, adds a further ingredient linked to a more even-looking complexion over time. Give it consistent morning use for several weeks before judging whether your skin's tone and texture have shifted.
What should come immediately after this serum in a morning routine?
This vitamin C serum is typically applied early, after toner and before a moisturizer or sunscreen step, since ascorbic acid performs best close to clean skin. Nothing on the ingredient list is known to conflict with a standard sunscreen applied over it. It is generally not layered in the same session as a separate strong exfoliating acid, so keeping those two treatments on different days or times of day is the more cautious approach.
How do I make sure this single bottle is the genuine Korean-market formula and not a repackaged substitute?
The barcode on this bottle, 8809598455238, is a genuine EAN specific to this product, so matching it against your packaging is a straightforward first check. COSRX also verifies units through its own system: enter the batch number and expiration date printed on your unit at the checking page on cosrx.com, reading the codes straight off the box. Using both checks together, rather than relying on a seller's claim, is the reliable way to confirm what you have.
Not on the ingredient list below: fragrance or parfum, denatured or SD alcohol, essential oils, silicones, parabens, sulfate surfactants, mineral oil or petrolatum and added color.
Full INCI (25): Water, Ascorbic Acid(13%), Butylene Glycol, Dipropylene Glycol, Tromethamine, 3-0-Ethyl Ascorbic Acid, Panthenol, Acetyl Glucosamine, Caffeine, Sodium Hyaluronate, Sodium Sulfite, Disodium EDTA, Glutathione, Adenosine, Gardenia Florida Fruit Extract, Allantoin, Dextrin, Squalane, Tocotrienols, Tocopherol, Elaeis Guineensis (Palm) Oil, Arginine, Niacinamide, Pentylene Glycol, Glycyrrhiza Glabra (Licorice) Root Extract
Ingredient list read from inkeedecoder.com on 18 August 2026.
25 of 25 explained
- Water solvent
- Water is the base almost every serum, toner and cream is built on. It dissolves the water-loving ingredients and sets how light the finished texture feels. On an INCI list it is usually first, which only means it is the largest single ingredient by weight.
- Ascorbic Acid(13%) antioxidant
- Ascorbic Acid is pure vitamin C, the most researched form and also the least stable: it needs a low pH and airtight packaging to stay active. It is an antioxidant used for the look of dullness and uneven tone.
- Butylene Glycol humectant
- Butylene Glycol is a small glycol that does two jobs at once: it holds water in the top layer of skin and it dissolves plant extracts and actives that plain water cannot. It also thins a formula, which is why watery Korean essences lean on it.
- Dipropylene Glycol humectant
- Dipropylene Glycol is a glycol used as a solvent and a light humectant. Its main job is keeping the rest of the formula dissolved and the texture fluid rather than adding hydration of its own.
- Tromethamine pH adjuster
- Tromethamine neutralises acidic thickeners such as carbomer so they gel, and holds a formula near skin-friendly pH. It is used at a fraction of a percent.
- 3-0-Ethyl Ascorbic Acid antioxidant
- 3-O-Ethyl Ascorbic Acid is a stable vitamin C derivative that skin converts to ascorbic acid. It survives in a formula far better than pure vitamin C and works at a gentler pH, so it suits skin that finds the pure acid uncomfortable.
- Panthenol humectant
- Panthenol is pro-vitamin B5: skin converts it to pantothenic acid. It is a humectant that holds water and leaves skin feeling soft and less tight, and it is one of the ingredients formulators reach for when a formula also contains something harsh.
- Acetyl Glucosamine active
- Acetyl Glucosamine is the sugar unit hyaluronic acid is built from. It is used as a humectant and, at higher levels, for the look of uneven tone, often paired with niacinamide.
- Caffeine active
- Caffeine constricts small blood vessels near the surface, which is why eye products use it for the look of puffiness and shadow. It is water soluble and works only while it is on the skin.
- Sodium Hyaluronate humectant
- Sodium Hyaluronate is the salt of hyaluronic acid, and it is what most products labelled hyaluronic actually contain. The salt dissolves more readily and the molecule is smaller, so it sits in the outer layer of skin rather than only on top of it.
- Sodium Sulfite antioxidant
- A reducing agent used to stop vitamin C and other easily oxidised ingredients from browning in the bottle.
- Disodium EDTA chelator
- EDTA is a chelator: it locks up trace metal ions from water and packaging that would otherwise turn a formula cloudy, off-colour or rancid. It does nothing to skin and appears at a fraction of a percent.
13 more explained
- Glutathione antioxidant
- Glutathione is a small peptide the body uses as one of its main antioxidants. In skincare it is used as an antioxidant and for the look of dullness; it is unstable in water, so formulas that carry it are usually built around protecting it.
- Adenosine active
- Adenosine is a nucleoside that Korea's own cosmetic authority recognises as a wrinkle-care functional ingredient, which is why it appears on so many Korean lists at a low level. It is used for the look of fine lines and is stable and well tolerated.
- Gardenia Florida Fruit Extract plant extract
- Gardenia Fruit Extract is the traditional East Asian yellow dye plant. In skincare it is used as an antioxidant extract, and it can tint a formula.
- Allantoin active
- Allantoin is a comfrey-derived compound used to condition skin and soften the outer layer so it feels smoother. It is one of the standard additions to a formula built for easily irritated skin.
- Dextrin thickener
- Dextrin is a starch fragment used to thicken and to give a formula a light, powdery finish. It is also a common carrier for powdered extracts.
- Squalane emollient
- Squalane is the stable, saturated version of squalene, a lipid human skin already makes. It is a light emollient that absorbs quickly, does not oxidise, and is one of the few oils widely considered safe for blemish-prone skin. Most cosmetic squalane is now from sugarcane or olive rather than shark.
- Tocotrienols antioxidant
- Tocotrienols are the other half of the vitamin E family, usually from rice or palm. They are oil-soluble antioxidants used alongside tocopherol.
- Tocopherol antioxidant
- Tocopherol is vitamin E. It is an oil-soluble antioxidant that protects the oils in a formula from going rancid and works on skin as an emollient, and it is regularly paired with vitamin C because each keeps the other going for longer.
- Elaeis Guineensis (Palm) Oil emollient
- Palm Oil is a rich emollient high in palmitic and oleic acids. In skincare it is more often a source material for esters and emulsifiers than an ingredient on its own.
- Arginine amino acid
- Arginine is an amino acid that does two jobs here: it holds water in the outer layer of skin, and it neutralises acidic gelling agents, which is why it often stands in for a synthetic pH adjuster.
- Niacinamide active
- Niacinamide is vitamin B3, and it is the most studied active in Korean formulation. It is used at roughly 2 to 5 percent for the look of uneven tone and visible pores, and it is water soluble, stable and comfortable beside almost every other active, which is why it turns up in so many lists.
- Pentylene Glycol humectant
- Pentylene Glycol hydrates and, like the other longer-chain glycols, makes a formula less hospitable to microbes so the preservative system can be lighter. It also improves how evenly a product spreads.
- Glycyrrhiza Glabra (Licorice) Root Extract plant extract
- Licorice Root Extract carries glabridin and liquiritin. It is one of the classic plant ingredients used for the look of uneven tone and redness, and it appears in almost every brightening formula that avoids synthetic actives.
- Market
- Korean market, the version sold in Korea
- EAN (barcode)
- 8809598455238
- Made in
- Republic of Korea
- Category
- Serum & Ampoule
- Actives
- Adenosine, Allantoin, Caffeine, Glutathione, Licorice Root, Niacinamide, Panthenol, Sodium Hyaluronate, Squalane, Vitamin C
- Ships from
- California or Korea
Orders ship from California or direct from Korea with tracked delivery to your door, and both routes carry the same Korean-market release. Shipping is free on orders of $100 or more. Returns are accepted for 30 days, by mail.
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 - 2Barcode
Listed against the Korean barcode on its box - 3California or Korea
Ships to you from either, as the same Korean-market release
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. The barcode in the specification above is the Korean-market one and it is printed on the box you receive.
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.
Every order ships from California or direct from Korea, 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.
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.
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.
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COSRX The Vitamin C 13 Serum (Single)
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COSRX, Korean-market original
Vitamin C 13% Serum, 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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