COSRX - The Vitamin C 23 Serum (20ml)

COSRX The Vitamin C 23 Serum is a high-strength pure vitamin C serum — potent, well-evidenced, and more demanding about storage and handling than anything else in the range.

The Vitamin C 23 Serum at a glance

Strength, stinging, and the colour test

Pure vitamin C is one of the best-supported actives available: it brightens, evens tone, and provides antioxidant protection that complements sunscreen against daily environmental damage. Used in the morning under SPF, it earns its place.

Two practical realities come with high concentrations. The first is tolerance — 23% is a lot, and stinging on application is common, particularly on sensitive or compromised skin. It is also worth knowing that absorption does not keep climbing indefinitely with concentration; research generally puts the useful ceiling around the 20% mark, above which you mostly gain irritation rather than effect. If this stings persistently, a lower-strength vitamin C is a reasonable and not inferior choice.

The second is stability. Pure vitamin C oxidises on contact with light, heat and air, and oxidised vitamin C does nothing useful. Judge it by colour: fresh product is clear to pale yellow. As it ages it turns deep yellow, then orange, then brown. Once it is orange it has largely degraded — that is the point to replace it, not to push on to the last drop. Keep the cap tight, store it away from the bathroom window, and expect a few months of useful life after opening.

A serum that has gone brown is not dangerous, simply spent.

How to use it

1. Use it in the morning on clean dry skin, before moisturiser.
2. Start every other day if you are new to high-strength vitamin C.
3. Apply a few drops, avoiding the eye area, and let it absorb.
4. Always follow with sunscreen — vitamin C and SPF work together, and neither replaces the other.
5. Close the cap tightly and store somewhere cool and dark.

Browse the full COSRX range at EmartGCC, or the Korean serums collection.

Frequently asked questions

My serum turned orange. Can I still use it?

It has oxidised and lost most of its potency. It is not harmful, but it is no longer doing much — replace it. Clear to pale yellow is fresh.

Is 23% better than a lower percentage?

Not necessarily. Absorption plateaus around 20%, so beyond that you tend to gain irritation rather than results. A lower-strength vitamin C is a perfectly good option, especially for sensitive skin.

It stings when I apply it. Is that normal?

A brief tingle is common with high-strength vitamin C. Persistent stinging or burning means it is too strong for your skin — reduce frequency or switch to a gentler formulation.

Morning or night?

Morning, under sunscreen. Its antioxidant protection is most useful during daytime exposure.

Can I use it with niacinamide?

Yes. The old advice against combining them came from lab conditions that do not reflect modern formulations. If you prefer, use one morning and one evening.

Can I use it with retinol?

Yes, but not at the same time. Vitamin C in the morning and retinol at night is the standard, well-tolerated arrangement.

How should I store it, and how long does it last?

Cool, dark, tightly sealed, and out of a steamy bathroom. Expect a few months of useful life once opened — go by colour rather than the date.

Buying COSRX in Kuwait

EmartGCC supplies 100% original COSRX with free standard home delivery across Kuwait, usually next day. Areas beyond Fahaheel and Jahra carry a 3 KD delivery surcharge. Cash on delivery is available, and unopened items can be returned within 14 days.