COSRX The Vitamin C 23 Serum Review: Strong, Simple, and Not for Everyone

A very short, very strong formula: 23% ascorbic acid (pure vitamin C) with hyaluronic acid, panthenol, allantoin and niacinamide. It can visibly brighten dull skin and fade dark marks over a few weeks.

It also tingles, can irritate sensitive skin and oxidizes faster than gentler forms of vitamin C. Great for skin that already handles actives. Not a beginner product.

Not necessarily. Studies on pure vitamin C suggest the benefits level off around 20%, while irritation keeps rising.

So 23% is not twice as good as 10 or 15%. It is mainly stronger. If your skin likes it, great. If it stings for more than a minute or leaves you red, a lower strength will give you most of the benefit.

Brightens dull, tired looking skin.

Helps fade the brown marks left by spots and sun, especially together with daily sunscreen.

Adds antioxidant protection under sunscreen in the morning.

Tingling is normal for the first minute. Burning, lasting redness or flaking is not. Stop or use it less often.

Pure vitamin C oxidizes. When the serum turns clearly yellow or brown, it has lost much of its power. Close the cap tightly, keep it cool and out of the sun, and use it up within a few months.

It can feel slightly tacky before it sinks in.

Mornings, on clean, dry skin, before moisturizer and always before sunscreen.

Start every second or third day for the first two weeks, then build up to daily if your skin is happy.

Don't use it in the same routine as AHA or BHA exfoliants. Retinoids belong in your night routine, so they don't clash.

Very sensitive or rosacea prone skin, and anyone whose barrier is currently damaged.

Beginners who have never used actives. Start with something gentler and come back later.

Beauty of Joseon Glow Deep Serum: Rice + Alpha Arbutin brightens with alpha arbutin and niacinamide and is much kinder to sensitive skin.

Klairs Freshly Juiced Vitamin Drop uses a lower dose of vitamin C and is a classic first vitamin C serum.

COSRX Advanced Snail Radiance Dual Essence combines snail mucin and niacinamide for a softer glow without the sting.