Advanced The Vitamin C 23 Serum
A morning vitamin C serum for a brighter, more even look, in a 20 g bottle, for skin already comfortable with a daily vitamin C step.
No reviews yet20 g
$10.59 per 10 g
- Korean-market formula
- Ships from California or direct from Korea
- Korean barcode and batch code intact
- Suited to
- NormalOilyCombinationNot recommended as a first vitamin C serum for sensitive or reactive skin
- Helps with
- Pronounced dullnessDark spots and hyperpigmentationSkin already comfortable with vitamin C wanting a stronger dose
In stock. Arrives in 3 to 7 business days
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You’re $100.00 away from free US shipping.
- 30-day returns
- Free US shipping on orders of $100 or more
- Tracked delivery to your door
Key benefits
- Ascorbic acid is declared at 23 percent, second on the list right after water
- 3-O-ethyl ascorbic acid at six is a second, more stable vitamin C form working alongside the primary one
- Tocotrienols at seventeen, a stronger antioxidant vitamin E form, and glutathione at twenty-three support and extend the vitamin C's effect
- Squalane and three plant oils toward the end of the list offset the dryness a high-percentage vitamin C can leave behind
- Niacinamide at twenty-one adds a fourth brightening mechanism to an already dense stack
- No fragrance, no parfum, no essential oil on the list
Key actives
2Ascorbic AcidDeclared at 23 percent, second on the list
One of the highest declared ascorbic acid concentrations in the store's catalog. Pure ascorbic acid is the most studied vitamin C form and the most likely to cause initial sensitivity, which is why this serum is positioned for skin already comfortable with vitamin C.
63-O-Ethyl Ascorbic AcidA second, more stable vitamin C form at position six
Less prone to oxidation than pure ascorbic acid, it extends the serum's brightening effect and helps the formula hold its potency longer once opened.
17TocotrienolsA vitamin E form with a stronger antioxidant profile than standard tocopherol, at seventeen
COSRX markets this as super vitamin E for its more potent antioxidant activity, included specifically to work alongside the ascorbic acid rather than as a standalone claim.
23GlutathioneAn antioxidant tripeptide positioned at twenty-three
Works alongside the vitamin C and vitamin E as a third antioxidant layer, a combination frequently used together in high-strength brightening formulas.
Inside the formula
Inside the formula
- 2Ascorbic Acid
- 63-O-Ethyl Ascorbic
- 17Tocotrienols
- 23Glutathione
Where each key active sits on the declared ingredient list, by entry number. Position is proportion: the further forward, the larger its share.
What is the COSRX Vitamin C 23 Serum for?
It is a high-strength brightening serum for pronounced dullness and dark spots, built on ascorbic acid declared at 23 percent, second on the list. A second vitamin C form, tocotrienols and glutathione work alongside it to extend and support the effect, for skin already comfortable with vitamin C rather than as a first one to try.
Is 23 percent too strong for my skin?
It can be, especially if you have not used vitamin C before or your skin runs sensitive. This concentration is built for people already comfortable with lower-strength vitamin C serums who want a stronger dose. Patch test first.
Will it cause dryness or irritation?
High-percentage ascorbic acid can be drying or mildly irritating on some skin, which is why squalane and three plant oils sit further down the list to offset that. Starting every other day rather than daily is a common way to build tolerance.
Can I use this with a retinoid or exfoliating acid?
Most people alternate a high-strength vitamin C serum with a retinoid or acid rather than layering them the same session, since combining several strong actives at once raises irritation risk. AM for vitamin C, PM for a retinoid is a common split.
How does this compare to buying COSRX from a US retailer?
COSRX verifies units itself. Find the verification page on cosrx.com and enter the batch number and expiration date printed on your unit, read off the package rather than from us, which is the point. 8800311121256, and batch code intact under the box.
Not on the ingredient list below: fragrance or parfum, denatured or SD alcohol, essential oils, parabens, sulfate surfactants, mineral oil or petrolatum and added color.
Full INCI (28): Aqua/Water, Ascorbic Acid (23%), Butylene Glycol, Dimethicone, Panthenol, 3-O-Ethyl Ascorbic Acid, Squalane, Sodium Hydroxide, Caffeine, Sodium Hyaluronate, Sodium Metaphosphate, Adenosine, Acetyl Glucosamine, Gardenia Florida Fruit Extract, Allantoin, Dextrin, Tocotrienols, Tocopherol, Elaeis Guineensis (Palm) Oil, Arginine, Niacinamide, Pentylene Glycol, Glutathione, Helianthus Annuus (Sunflower) Seed Oil, Methyl Trimethicone, Carthamus Tinctorius (Safflower) Seed Oil, Camellia Japonica Seed Oil, Daucus Carota Sativa (Carrot) Root Extract
Ingredient list read from jolse.com on 9 September 2026.
28 of 28 explained
- Aqua/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 (23%) 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.
- Dimethicone silicone
- Dimethicone is the most used cosmetic silicone. It forms a breathable film that smooths the surface, slows water leaving skin, and gives the slip that makes a primer or cream feel silky. It is inert and does not penetrate.
- 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.
- 3-O-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.
- 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.
- Sodium Hydroxide pH adjuster
- Sodium Hydroxide is a strong base used in traces to bring an acidic formula up to skin-friendly pH. None of it remains as itself once the formula is neutralised.
- 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 Metaphosphate chelator
- A phosphate salt that ties up metal ions in water. It also stops the calcium and magnesium in hard water from flattening a cleanser foam.
- 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.
16 more explained
- 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.
- 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.
- 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.
- 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.
- Helianthus Annuus (Sunflower) Seed Oil emollient
- Sunflower Seed Oil is high in linoleic acid, the fatty acid dry and blemish-prone skin is often short of. It is a light, non-fragrant emollient and one of the better tolerated plant oils.
- Methyl Trimethicone silicone
- Methyl Trimethicone is a light, volatile silicone chosen for a notably dry finish. It thins a formula and disperses powders evenly.
- Carthamus Tinctorius (Safflower) Seed Oil emollient
- Safflower seed oil, among the highest-linoleic plant oils. High-linoleic oils feel lighter and absorb faster than high-oleic ones.
- Camellia Japonica Seed Oil emollient
- Camellia Seed Oil is the traditional Korean and Japanese hair and skin oil, high in oleic acid. It is a light emollient that absorbs quickly for its richness.
- Daucus Carota Sativa (Carrot) Root Extract plant extract
- Carrot Root Extract carries carotenoids, which give it a strong orange colour. It is used as an antioxidant extract and can tint a formula.
- Market
- Korean market, the version sold in Korea
- EAN (barcode)
- 8800311121256
- Made in
- Republic of Korea
- Volume
- 20 g
- Category
- Serum & Ampoule / Vitamin C Serum
- Actives
- Adenosine, Allantoin, Caffeine, Glutathione, 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 in a morning routine, in COSRX's 20 g size. It goes on after toner, on dry skin, and before moisturizer and sunscreen. What it works on is tone: a brighter, more even look that builds over weeks of daily mornings rather than in a single application. Skin new to a vitamin C serum usually does better starting every other morning and building up from there. It suits someone who already has a cleanser, a toner and a sunscreen in place and wants one active step between them.
How to use
- AM, after toner, as a brightening step. Start every other day if you are new to vitamin C at this strength.
- A few drops pressed evenly over the face, avoiding the eye area where skin is thinner and more reactive.
- Let it fully absorb, several minutes if needed, before layering anything else on top.
- Follow with moisturizer and sunscreen without fail, since vitamin C works best paired with daily sun protection.
Worth knowing
- This is a 23 percent ascorbic acid serum, one of the most concentrated vitamin C formulas in our catalog. If you have not used vitamin C before, start with a lower-percentage serum first.
- Ascorbic acid at this concentration can sting on compromised, freshly exfoliated or very sensitive skin. Patch test before applying to the full face.
- Sodium hydroxide is present to adjust pH for the ascorbic acid's stability, not as a treatment ingredient.
Complete the routine
- This itemCOSRX Advanced The Vitamin C 23 Serum$21.17
- Seal the routine in as the last stepCOSRX Skin Barrier Moisturizing Cream 450ml$42.50
- An as-needed step, in place of the prep layerCosrx 5 PDRN Hyaluronic Acid Vital Hydrating Hydrogel Mask$4.70
Total for 3 items$68.37
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Cosrx Advanced The Vitamin C 23 Serum
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COSRX, Korean-market original
The Vitamin C 23 Serum, 20 g, 23% ascorbic acid second on the list.
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 skin care, 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 Pretty much every step of a Korean skin care routine is going to have some component of hydration.
Alok Vij, MDDermatologist, Cleveland Clinic
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