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COSRX The Vitamin C 23 Serum 20ml | Sleepy Hello

COSRX

COSRX The Vitamin C 23 Serum 20ml

Brightens

Hydrating

Smooths

Antioxidant

PRODUCT DETAILS

COSRX The Vitamin C 23 Serum is the high-strength end of the brand's vitamin C range, built around 23% pure ascorbic acid in a 20ml dropper bottle. It belongs at the serum step, going on after your toner and before moisturizer.

The formula separates into two layers on the shelf, so a gentle shake brings them back together before each use. Ascorbic acid does the visible tone work, and tocotrienols — what COSRX calls Super Vitamin E — sit alongside it as a second antioxidant. Sodium hyaluronate and panthenol hold water at the surface, allantoin keeps the finish comfortable, and a light layer of squalane with camellia and safflower seed oils softens the drag a strong acid serum can otherwise leave.

Dull, uneven-looking skin is where it earns its place, and it settles to a dewy finish rather than a matte one. COSRX builds the 13% version for people newer to vitamin C and calls that one the everyday choice for reactive skin, so think of 23% as the step up once a lower strength already sits comfortably.

The bottle is deliberately small. Pure ascorbic acid is reactive, so COSRX suggests refrigerating it once opened and finishing it inside two months. There is no added fragrance, though vitamin C carries a faint scent of its own. Patch test on your wrist or neck before the first full application.

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GOES WELL WITH

ANUA Niacinamide 5 + TXA Brightening Pad 210ml (60 pads)$24.00

ANUA Peach 77 Niacin Essence Toner 250ml$25.00

ANUA Rice Enzyme Brightening Cleansing Powder 40g$20.00

Anua Rice 70 Glow Milky Toner 250ml$23.00

Banila Co Clean It Zero Cleansing Balm Original 100ml$24.00

100 Reedle Shot Stick Pouch$11.52

1025 Dokdo Cleanser$17.00

1025 Dokdo Eye Cream$35.00

COSRX's most concentrated vitamin C serum, made for people who want noticeable tone work rather than a gentle daily top-up.

Visibly brighter, more even tone
Two antioxidants, not one
A cushioned, dewy finish
Sized to stay fresh

Frequently asked questions

Can I use The Vitamin C 23 Serum every day?

COSRX says yes, daily use is fine — but this is a high concentration of pure vitamin C, and it may sting or flush the skin at first. The brand asks for a patch test, a little on the inner wrist or the neck, before you commit to a whole face. If your skin feels uncomfortable, use it less often and build up slowly, or pair it with a moisturizer. If that does not settle it, stop.

Should I use it in the morning or in the evening?

COSRX's own directions put it after cleansing and toner, then moisturizer and sunscreen during the day, so we file it as a morning step. Vitamin C is an antioxidant, which is the job it does best while you are out in daylight. Using it at night works too. Either way, keep sunscreen in your morning routine, because it matters more once a strong active is part of your week.

Is 23% too strong if I have never used vitamin C?

Most likely, yes. COSRX makes The Vitamin C 13 Serum for people starting out and describes it as the everyday option for reactive skin, while this one is positioned for intensive care by experienced users. Pure ascorbic acid at 23% can sting or leave skin flushed if it has not built up tolerance. If vitamin C is new to you, begin at 13% and move up when that feels easy.

Why does the serum separate in the bottle?

That is by design. This formula carries a water phase and a light oil phase of squalane, camellia, and safflower seed oils, and the two settle apart between uses. Shake the bottle gently before you draw the dropper up so they recombine. That oil layer is also why this version feels more cushioned on the skin than the 13%, which absorbs faster and leaves less of a finish behind.

How should I store it, and does the colour matter?

COSRX suggests refrigerating the bottle once opened and using it up within two months; unopened, it keeps for 24 months from the manufacturing date. Pure ascorbic acid is reactive, which is why the bottle is only 20ml. A pale yellow tint is normal and expected. If it turns deep orange or brown, the vitamin C has degraded and the serum is past useful life, so replace it.

What should I avoid using alongside it?

COSRX advises against layering it with AHA or BHA exfoliating acids, since that pairing is a common source of irritation. The brand also suggests keeping it apart from copper peptide products and from other strong actives such as retinol — put those at the opposite end of the day. Partners COSRX names as sensible include hyaluronic acid, ceramides, centella, and snail mucin.

Does it have a smell?

There is no added fragrance here. Pure vitamin C has a faint scent of its own that some people read as slightly sharp or metallic, and COSRX confirms this is normal rather than a sign the bottle has turned. It usually fades within a minute of application. A strongly sour smell arriving together with a deep orange colour is a different matter, and points to oxidation.

Key Ingredients

Hyaluronic Acid

Allantoin

Full ingredients

Concerns & Benefits

Your Concerns

Our Benefits

How To Use

Frequently asked questions

Customer reviews

Frequently Bought Together

Key Ingredients

Hyaluronic Acid

Allantoin

Concerns & Benefits

Your Concerns

Our Benefits

How To Use

Frequently asked questions

Customer reviews

Frequently Bought Together

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