How often should I use it?

Start once daily or a few times a week, depending on your skin's comfort, then increase only if it remains comfortable. COSRX's exact-product directions allow morning or evening use. A higher frequency is not automatically better; scale back if you notice persistent stinging, redness, tightness or dryness.

Can I use it with vitamin C, exfoliating acids or retinoids?

COSRX advises keeping strong vitamin C, exfoliating acids and retinoids out of the same application. You can alternate morning and evening or use them on different days. If a retinoid is prescribed, follow your clinician's instructions and introduce any new product cautiously.

Where does it go in my routine?

Use it after cleansing and toning but before moisturizer. Shake the bottle gently once or twice, spread two to three drops across the face or target areas, and pat until absorbed. In the daytime, finish with sunscreen. Avoid direct contact with the eyes.

Can I use it morning and night?

The exact-product directions allow morning or evening use, and the stored COSRX graphic describes once- or twice-daily application. Start more slowly if you are new to high-strength niacinamide. When it is part of a morning routine, complete your skincare with sunscreen.

How is it different from COSRX BHA Blackhead Power Liquid?

This serum focuses on visible oil balance, uneven tone, enlarged-looking pores and post-breakout marks through niacinamide, acetyl glucosamine and Zinc PCA. The BHA Blackhead Power Liquid is an exfoliant built more directly around pore buildup and blackheads. Choose based on your primary goal instead of assuming they are interchangeable.

An official COSRX response on Ulta says the high concentration may sometimes form clumps and advises removing them before use. If the product has changed smell or color, leaked, or appears contaminated, stop using it and contact the retailer or COSRX rather than trying to diagnose the bottle yourself.

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COSRX

The Niacinamide 15 Serum 20ml

Oil control
Smooth texture
Even tone
Quick absorbing

20ml ·$16.99 USD

Oil control

Smooth texture

Even tone

Quick absorbing

PRODUCT DETAILS

COSRX The Niacinamide 15 Serum is a lightweight, fast-absorbing formula for oily, combination and blemish-prone skin. The concentrated serum helps visibly balance excess oil, refine the look of enlarged pores and brighten the appearance of post-breakout marks without leaving a heavy finish. Its clear texture slips easily into morning or evening routines and layers under moisturizer or sunscreen.

At the center is 15% niacinamide, paired with acetyl glucosamine and Zinc PCA. This combination is positioned to support a more even-looking tone, help manage visible shine and keep pore congestion from dominating the complexion. Allantoin adds a soothing, skin-softening touch, while trehalose supports a comfortable, hydrated feel.

Choose this if your main concerns are recurring shine, noticeable pores, uneven texture or flat marks left after blemishes. It is a high-strength niacinamide serum, so more is not necessarily better: start with a few drops, patch test first and reduce frequency if your skin feels uncomfortable. COSRX recommends separating it from high-strength vitamin C, AHA/BHA and retinoid products rather than applying them in the same routine.

Apply after cleansing and toning, then follow with moisturizer. If used in the morning, finish with sunscreen. With continued use, the formula is designed to leave skin looking clearer, smoother and more balanced.

Learn more

GOES WELL WITH

ANUA Heartleaf Pore Control Cleansing Oil Mild 200ml$16.99 USD

ANUA Heartleaf Quercetinol Pore Deep Cleansing Foam 150ml$10.99 USD

ANUA Heartleaf Succinic Moisture Cleansing Foam 150ml$10.99 USD

ANUA Heartleaf Pore Control Cleansing Oil 200ml$15.99 USD

ARENCIA Fresh Green Rice Mochi Cleanser 120g$18.99 USD

ANUA Heartleaf 77% Soothing Toner 250ml$15.99 USD

Anua Rice 70 Glow Milky Toner 250ml$15.99 USD

100 Reedle Shot Stick Pouch$8.09 USD

A focused set of tone, texture and oil-balance benefits makes this high-strength serum most useful for congested-looking, shiny skin.

Balances visible oiliness
Refines enlarged-looking pores
Brightens post-breakout marks
Smooths rough texture
Layers without heaviness

Key Ingredients

Niacinamide

Helps visibly brighten uneven tone and support the skin barrier.

A flowing band of apricot, celadon, coral and lavender marbling crosses textured warm-ivory paper.

Trehalose

A defined non-reducing disaccharide used as a humectant and moisturizer. It can support a water-focused formula, but label presence cannot prove dose or results.

Three oversized translucent, softly faceted glass crystals arranged on a pale lavender stage above a blush background with a small coral accent.

Allantoin

Helps soothe and soften dry, rough-feeling skin.

Real Results

50%Decrease in measured whitehead count after 4 weeks¹
48.1%Improvement in measured facial oiliness after 4 weeks¹
45.3%Reduction in measured visible pore count after 4 weeks¹
42.3%Decrease in measured blackhead count after 4 weeks¹
19.5%Improvement in measured pigmentation appearance after 4 weeks¹

View all 9 real results

Open COSRX The Niacinamide 15 Serum bottle with its dropper holding a clear serum drop against white.

Concerns & Benefits

Your Concerns

1
Oiliness
Skin that looks shiny again soon after cleansing, especially through the T-zone.
2
Enlarged Pores
Pores that appear more noticeable when oil and uneven surface texture collect.

How To Use

1Shake the bottle gently once or twice. After cleansing and toning, dispense two to three drops and spread a thin layer over target areas or the face. Pat lightly until absorbed.
2Follow with moisturizer. When you apply the serum during the day, finish with sunscreen.
3Patch test first and introduce the formula gradually. Avoid direct eye contact. Place potent vitamin C, exfoliating acid or retinoid steps in a separate routine or on another day, following COSRX's guidance.

Close-up of a dropper dispensing clear serum onto a model's cheek.

Frequently asked questions

Who is this serum best for?

COSRX positions it for all skin types, with the strongest fit for oily, combination and blemish-prone skin concerned with shine, noticeable pores and post-breakout marks. Because 15% niacinamide is a high concentration, sensitive or dry skin should patch test and introduce it gradually rather than beginning with frequent use.

Keep learning

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This itemThe Niacinamide 15 Serum 20ml$16.99 USD

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COSRX The Niacinamide 15 Serum 20ml | Sleepy Hello

COSRX

The Niacinamide 15 Serum 20ml

Oil control
Smooth texture
Even tone
Quick absorbing

The Niacinamide 15 Serum 20ml

20ml ·$16.99 USD

Oil control

Smooth texture

Even tone

Quick absorbing

PRODUCT DETAILS

Learn more

GOES WELL WITH

ANUA Heartleaf Pore Control Cleansing Oil Mild 200ml$16.99 USD

ANUA Heartleaf Quercetinol Pore Deep Cleansing Foam 150ml$10.99 USD

ANUA Heartleaf Succinic Moisture Cleansing Foam 150ml$10.99 USD

ANUA Heartleaf Pore Control Cleansing Oil 200ml$15.99 USD

ARENCIA Fresh Green Rice Mochi Cleanser 120g$18.99 USD

ANUA Heartleaf 77% Soothing Toner 250ml$15.99 USD

Anua Rice 70 Glow Milky Toner 250ml$15.99 USD

100 Reedle Shot Stick Pouch$8.09 USD

A focused set of tone, texture and oil-balance benefits makes this high-strength serum most useful for congested-looking, shiny skin.

Balances visible oiliness
Refines enlarged-looking pores
Brightens post-breakout marks
Smooths rough texture
Layers without heaviness