COSRX Advanced The Vitamin C 23 Serum 20g × 2

Two 20g bottles: open one at a time and refrigerate at 3–10°C.

Best for

Someone comparing a 23% pure-vitamin-C serum together with its opening and storage requirements.

Format

Serum

Contents

2 pcs

₩24,500 per unit

KFDA claims

Brightening (KFDA) · Anti-wrinkle (KFDA)

₩49,000

Retail price in Korea (KRW) at the time of listing. Actual prices may vary.

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What it is

For a two-bottle vitamin C promotion, opening order and storage matter alongside concentration. Advanced The Vitamin C 23 is the Korean formula labeled with 23% ascorbic acid, a pure vitamin C ingredient. This set contains two 20g bottles, not a single 40ml container.

Distinguish Advanced from the older formula

The Korean list begins with water, ascorbic acid and butylene glycol and includes panthenol, squalane, 3-O-Ethyl Ascorbic Acid, tocotrienols and tocopherol. Ascorbic acid and its derivative are different ingredients; 23% does not apply to each one. An older international Vitamin C 23 list places propanediol near the beginning, so similar names do not justify exchanging the formulas.

Do not shake before the first opening

Official directions distinguish attaching the supplied dropper from gently shaking side to side afterward. Apply an appropriate amount after cleansing, starting on the cheeks and spreading outward. Use sunscreen during the day. A concentrated label is not a reason to use more product or stronger massage.

Refrigeration and the two-month period

Refrigerate at 3–10°C upon purchase and use within two months of opening. Packaging directions note that gas or a popping sound can occur at first opening, reinforcing the instruction not to shake beforehand. Do not interpret an unsuitable skin reaction as a sign of effectiveness to endure. Manage one bottle at a time and prioritize the actual packaging if versions have different use or storage instructions.

A buying question answered

The set is two 20g bottles; grams are not converted to ml. With a two-month opened period, opening one bottle at a time makes the bundle easier to manage. Do not substitute directions from the older international Vitamin C 23 formula.

Use and comparison choices

Do not shake before first opening. Attach the supplied dropper, then shake gently from side to side. After cleansing, apply an appropriate amount during the skin-care step, starting on the cheeks and spreading gently outward. Follow with moisturizer and daytime sunscreen. Close securely, refrigerate at 3–10°C and use within two months of opening.

Alpha-Arbutin serum is a different formula to compare. Choose the step you need before introducing both concentrated serums at once.

Follow with cream as needed after serum settles, without premixing the products for storage.

References

Source 1 · Source 2

This guide covers the Korean listing; localized ingredient names are editorial translations. Check your regional pack.

What works

The Korean Advanced formula lists ascorbic acid 23%, panthenol and squalane.
20g × 2 sales size; compare other sizes and extras separately.

What to watch

Directions specify refrigeration at 3–10°C upon purchase and use within two months of opening. Do not shake before opening.

Skip it if

A listed ingredient has caused a reaction, or the area is wounded or reacting.

Key ingredients

Vitamin CEWG 1
Pure, underivatised vitamin C, the most heavily researched form for antioxidant defence and tone. Unlike derivatives it acts without needing conversion in the skin, but it is highly vulnerable to light and air, browning quickly and staying stable only at low pH. That is why it often ships in airless packaging or as a powder.
PanthenolEWG 1
A precursor to vitamin B5 that converts to pantothenic acid once absorbed. It works in two directions at once, holding water and helping settle the skin barrier, which is why it appears in both calming skincare and hair care. Its low irritation profile makes it a regular in sensitive-skin formulas.
SqualaneEWG 1
Squalene with hydrogen added so it no longer goes rancid, closely matching a lipid the skin already produces in sebum. That similarity is why it absorbs without sitting on top, and while it once came from shark liver, olive and sugarcane are now the usual sources.

Description

How to use and where it fits

1
Do not shake before first opening. Attach the supplied dropper, then shake gently from side to side.
2
After cleansing, apply an appropriate amount during the skin-care step, starting on the cheeks and spreading gently outward.
3
Follow with moisturizer and daytime sunscreen. Close securely, refrigerate at 3–10°C and use within two months of opening.

Questions people ask

How do I use it?

Should both bottles be opened, and is this 40ml?

What can I pair with or compare?

COSRX The Alpha-Arbutin Serum 50ml (+ Peptide Serum 30ml Gift): The main serum lists alpha-arbutin 2%, tranexamic acid and niacinamide. Alpha-Arbutin serum is a different formula to compare. Choose the step you need before introducing both concentrated serums at once. Follow with cream as needed after serum settles, without premixing the products for storage.

Full Ingredients

Water, , Butylene Glycol, Dimethicone, , 3-O-Ethyl Ascorbic Acid, , Sodium Hydroxide, , , Sodium Metaphosphate, , , Gardenia Florida Fruit Extract, , Dextrin, Tocotrienols, , Elaeis Guineensis (Palm) Oil, Arginine, , Pentylene Glycol, , Sunflower Seed Oil, Methyl Trimethicone, Carthamus Tinctorius (Safflower) Seed Oil, Camellia Japonica Seed Oil, Daucus Carota Sativa (Carrot) Root Extract, , Beta-Carotene…