I'm sure everyone knows that vitamin C is good for us. Today, we would like to talk in detail about it, as vitamin C is one of the most effective nutrients for our skin.

Let's start with its main effects.


▶ The benefits of vitamin C


When free radical, which results from internal/external stress, builds up as activated oxygen in our body, it disturbs the healthy skin cells and causes aging. However, the core function of vitamin C is to remove this toxic free radical and prevent skin aging.
[Reference] Vitamin C Inhibits NF-kB Activation by TNF Via the Activation of p38 Mitogen-Activated Protein Kinase, J Immuol. 2000 Dec 15;165(12):7180-8




When our skin is exposed to UV, the melanin cell that is deep inside our skin produces melanin pigment and occurs discoloration, such as freckles and blemishes. Vitamin C blocks this pathway of melanin pigmentation, eventually improving skin tone.
[Reference] Effective L-Tyrosine Hydroxylation by Native and Immobilized Tyrosinase, PLOS ONE, 11(10): e0164213 (2016)



Vitamin C is one of the core elements to make collagen, an essential component of our skin. And if we lack vitamin C, collagen synthesis decreases, and the skin loses elasticity.

Therefore, vitamin C is an ingredient that fills collagen, improving elasticity and wrinkles.
[Reference] Vitamin C, Collagen, and Cracks in the Plaque, Circulation Volume 105, Issue 12, 26 March 2002; Pages 1396-1398


▶ The character of Vitamin C

Pure Vitamin C is volatile and oxidized easily by various factors such as air exposure, UV exposure, pH, and temperature. As the oxidation progresses, it features a dark yellow color, which might even turn brown when it advances too much.


Despite the instability, vitamin C is still the most beloved ingredient due to its excellent skin efficacy. And to control pure vitamin C, various vitamin C derivatives have been developed and are actively being used. Vitamin C derivatives are well known to be good for our skin as specific chemical reactions and enzyme actions convert them into pure vitamin C. However, it is an early stage to be sure that vitamin C derivatives have the same effect as pure vitamin C as it needs to be clarified how it gets converted and how much it does.
[Reference] Topical L-Ascorbic Acid: Percutaneous Absorption Studies• Dermatol Surg 2001;27:137–142

Therefore, pure vitamin C, ascorbic acid, is the most recommended ingredient for proper effect.

Pure vitamin C has excellent skin absorption, and a study says that the amount of vitamin C increases in a short period due to this reason.

Also, we can expect better effects when used consistently than used only once, as it will maintain the vitamin C in our skin.
[Reference] Topical L-Ascorbic Acid: Percutaneous Absorption Studies• Dermatol Surg 2001;27:137–142

*So just like we take vitamin supplements daily, using vitamin C products consistently is important.

To support the effect of a vitamin C product, optimal pH should be applied, considering not only the content of vitamin C but also skin absorption rate and stability.

Studies have shown that ascorbic acid absorbs better to the skin when the pH condition is stronger.[Reference] Topical L-Ascorbic Acid: Percutaneous Absorption Studies• Dermatol Surg 2001;27:137–142

However, products with strong acidic are not recommended pH conditions as they might irritate normal skin which is slightly weakly acidic.

Considering the character of vitamin C and our skin, the best pH condition for a vitamin C skincare product is approx. pH 3.0-4.5.


▶ Vitamin C products at COSRX 

COSRX has two vitamin C derma products combining pure vitamin C (ascorbic acid) in high percentages. The two products contain 13% and 23% of ascorbic acid and the same active ingredients, such as tocotrienol (super vitamin E), hyaluronic acid, and allantoin. You can expect similar effects from the two products, but the two options are available for you to select depending on your desired strength and feel.

*For more information of the product,

▶ Vitamin C product guide

 Keeping products with high contents of pure vitamin C refrigerated is the best way to keep the vitamin C fresh. Also, it is highly recommended to close the lid (dropper) after using the product and keep it away from high temperatures or direct sunlight. It is best to finish using the product within the expiration date after the first opening.

 *Using sunscreen together adds effect when you use the vitamin C product during the day.


 *For more information of the product,


Depending on your skin type, you may feel slight dryness or skin tightening after using the vitamin C product. Using a moisturizing/hydrating cream together will help balance the finish.

As we take vitamin supplements daily, start your healthy skin care
 by using vitamin C cosmetic products. ✨






February 27, 2023 — cosrx inc


Lin Elgin said:

I’ve never used Vitamin C in my skincare become I’m afraid to use it on my face because of Rosacea due to an Anti Immune Condition. But I’d like to use a gentle Vitamin C. Would the Vitamin C 13 help if I mixed it with my moisturizer?

Lo said:

Love the tip about keeping it in the fridge to extend the shelf life!

Natalie said:

I’ve been looking into how to incorporate vitamin c in my skin regime. This article was extremely informative!

Thomas said:

i love the vitamin C

N said:

I love vitamin c so much!

Kara said:

Finally a good explanation on the benefits of vitamin c! Can’t wait to buy more products now!!! Love this skin care brand.

Marteena said:

Great news

Ngem said:

Good to be reminded of the important roles that Vitamin C has in our skin barrier. Thanks!

Sahira said:

Hoping to try it out this brand has never let me down

yasmine said:


Kim Nadela said:

Love your products!

Mandy said:

Wish I would have read this prior to finalizing my order. I will definitely be adding to next purchase.
Thank you for the info!

laiba noor said:

I didn’t know about Vitamin C oxidization . Blog was helpful. Thanks

Gabrielle said:

Was just thinking about adding vitamin c to my skin care routine! Thanks for the info!

Mel said:

Very effective

Kara said:

Thanks for the knowledge on vitamin C

Beth H said:

Currently using Vitamin C 23. Thanks for letting me know consistency is the way to use this.’

Sarah Stodder said:

This was very clear and educational, thank you! I feel like I understand more now.

Kelly said:

Good information

Gobluesuz said:

Very helpful info and cleared up a lot of questions I had.

Crystal C. said:

Really helpful information!

Mahfuza said:

Have been using bit c for a long time and I do see good results with it.

Joselin said:

New to skincare, great read!

Precious said:

This was very helpful when it comes to figuring what would work best for me!

Lily said:

Thw power of Vitamin C

JoAnn said:

Very informative, I’ve been looking for vitamin C products and love how all the information was broken down here

Anushka Kumari said:

Vitamin C really do wonders to our skin and which actually brightens our skin.

Blake said:


Maydo Barcellano said:

Best affordable product

Maydo Barcellano said:

Love Cosrx

Krista said:

I really love cosrx vitamin C, it brightens my skin and removes any acne blemishes. I use it in the morning following up with the cosrx aloe sunscreen

Becky C said:

Excellent and informative read

Navya Sree said:

Great information

Ailyn said:

This reminded me the importance of Vitamin C

Austen said:

love yall’s blog. so helpful!

Lacy Bowen said:

I love how informative this article is. I definitely learned a few things.

Leena said:

Explained well!

Dylan Cruickshank said:

I’ve been using the Vitamin C 23 serum for months now and my skin is so bright! But I didn’t realize it was also helping with elasticity. Thanks for the lesson!

Sharon said:

Great read!

Nicole Ward said:

Thank you for the educational information

Alice said:

Really love vitamin C. This is well explained

Meli said:

Can the brightening effects of vitamin C be permanent if used consistently for 1 year?

Tassia Dickenson said:

great info

Casey said:

I never knew vitamin c is one of the ingredients to make collagen. This is really interesting to know about.

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