Is 13% pure Vitamin C suitable for daily use?

Yes. Start 2–3 times per week and build to daily as tolerated. Always use sunscreen in the morning.

Can I layer it with niacinamide or retinoids?

It pairs well with niacinamide. If using strong actives (retinoids/AHAs/BHAs), alternate days or split AM/PM based on sensitivity.

How should I store this to keep it stable?

Keep upright in the refrigerator (about 3–10 °C), away from heat and light. Use within 2 months after opening.

The bottle makes a sound or releases gas when opened—is that normal?

With high-strength Vitamin C, minimal gas release or sound on opening can occur. It does not affect normal use.

When can I expect to see results?

Hydration can be noticed immediately; brighter, more even-looking tone typically appears within 2–4 weeks of consistent use.

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COSRX

COSRX The Vitamin C 13 Serum 20ml / 0.67 fl oz

Name: COSRX The Vitamin C 13 Serum 20ml / 0.67 fl oz
Brand: COSRX
Price: 12.99 USD
Availability: InStock

$12.99 USD

~~$19.59 USD~~ $12.99 USD

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COSRX The Vitamin C 13 Serum 20ml

A daily-toning booster with 13% pure L-ascorbic acid to visibly brighten dull tone, even texture, and address early signs of aging—while keeping skin comfortably hydrated. The stabilized formula balances efficacy and tolerance with an optimized pH and a synergy complex of antioxidants and soothing humectants.

Key Benefits

Pure Vitamin C 13% – daily-strength brightening and tone-evening care
Antioxidant defense – helps neutralize free radicals to support a healthier-looking complexion
Early-age care – improves the look of fine lines and photo-dullness
Hydration & comfort – lightweight, non-sticky finish suitable for everyday use
Optimized pH – balances stability of Vitamin C with skin compatibility

Why It Works

Pure L-ascorbic acid is a gold-standard brightener that also supports collagen look and addresses signs of oxidative stress. A supporting network of antioxidants—Tocotrienol (super Vitamin E), Tocopherol, and Glutathione—enhances stability and efficacy, while Niacinamide (tone care), Adenosine (wrinkle care), and a soothing trio of Panthenol, Sodium Hyaluronate, and Allantoin help keep skin calm and hydrated.

Results

After one use: hydration recharge reported (up to +113.7%)*
After 4 weeks: visibly brighter, more even-looking tone and reduced appearance of blemish marks*
Comfortable daily wear with a light, fresh finish

*Based on internal evaluation of the formula; individual results may vary.

How to Use

After cleansing and toner, apply 2–3 drops to face and neck, avoiding immediate eye area.
Press to absorb; follow with moisturizer. Introduce 2–3 times per week, then increase as tolerated.
Use sunscreen in the morning when applying Vitamin C.

Storage & Handling

Refrigerate upright (about 3–10 °C). Keep away from heat and direct light.
Use promptly after purchase; best within 2 months after opening.
A slight scent, gas release, or sound on opening can occur with high-strength Vitamin C.
Do not shake before first opening. After attaching the dropper, gently tilt side-to-side before use.

Recommended For

Dull, uneven tone and blemish marks
Those new to pure Vitamin C seeking daily use at a balanced strength
Skin needing both toning and hydration in one step
Early signs of aging (fine lines, photo-dullness)

Product Specs

Brand / Line	COSRX / The Vitamin C
Type	Daily brightening serum with pure L-ascorbic acid
Size	20ml / 0.67 fl oz
Key Components	13% L-ascorbic acid, Tocotrienol, Tocopherol, Glutathione, Niacinamide, Adenosine, Panthenol, Sodium Hyaluronate, Allantoin
Skin Concerns	Dull tone, blemish marks, uneven texture, early fine lines
Skin Type	All skin types; introduce gradually on sensitive skin