COSRX Advanced The Vitamin C 23 Serum 20g

23% Pure Vitamin C Intensive Brightening Serum

This is an intensive care serum formulated with 23% pure vitamin C (ascorbic acid), not a derivative. If dark spots, hyperpigmentation, or a dull complexion are your concerns, this is the product to reach for. Enhanced with super vitamin E (tocotrienol), it amplifies vitamin C's antioxidant power. The dual-phase formula includes an oil layer, so despite the high concentration, it glides on smoothly with a rich, cushiony feel. Panthenol, hyaluronic acid, and allantoin deliver hydration and soothing care in one step.

Clinically Proven Improvements in Tone, Radiance, and Texture

A human application test conducted on 20 adult participants confirmed a range of skin improvements.

• Skin texture improved by 92.32%
• Skin radiance improved by 34.81%
• Inner melanin improved by 14.15%
• Skin luminosity improved by 15.06%
• Surface elasticity improved by 15.07%
• Dark spot marks improved by 8.87%

Clinical testing also demonstrated a 5-way improvement in hyperpigmentation—including the number of dark spots, hidden spots, and spot area—along with visible benefits for eye wrinkles and pore care.

Gentle Formula Safe for Sensitive Skin

For those who've been hesitant about high-concentration vitamin C, this serum has completed low-irritation testing. It passed the primary skin irritation test, sensitive skin irritation test, and non-comedogenic test, making it suitable even for acne-prone skin. Especially recommended if you're dealing with a dull complexion, hyperpigmentation, and loss of elasticity all at once. Since pure vitamin C oxidizes easily, it's best to store the serum in the refrigerator after opening and use it within two months.

A targeted treatment for your serum step

After toning, apply this during your essence or serum step. With a potent 23% pure vitamin C formula, it's best used on its own rather than layered with other serums. Follow with a moisturizer to lock in the active ingredients and prevent them from evaporating.

Best used as an intensive evening treatment

While vitamin C can be used morning and night, this high-strength 23% formula is recommended for intensive care in your evening routine. If you do use it in the morning, always follow with a thorough application of sunscreen. First-time users may want to start with every other day to monitor how their skin responds.

Dispense gently with the dropper

This is a bi-phase serum, so give the bottle a gentle shake from side to side before use to mix the layers. Dispense 2–3 drops with the dropper and smooth over the entire face. For areas with dark spots or hyperpigmentation, apply a second layer. Press gently with your palms to help absorption.

Routine pairings by skin concern

• For a dull complexion: Layer niacinamide toner → vitamin C serum → moisturizer to focus on brightening
• For loss of firmness: Apply a peptide booster serum first, then follow with this product for anti-aging synergy
• For targeting dark spot marks: Consistent use for at least 4 weeks is needed to see visible results

Storage and precautions for high-strength vitamin C

After opening, store upright in the refrigerator (3–10°C) and use within 2 months. Do not use at the same time as retinol or AHA/BHA products — separate them into morning and evening routines for safety. Also avoid using simultaneously with blue peptide serums or creams. This formula is fragrance-free, so you may notice a natural ingredient scent. The color may deepen as it oxidizes — discontinue use if discoloration becomes significant.

Product ingredients list.

The list of ingredients is subject to change. Please consult the packaging of the product purchased.