Affordable K-Beauty vitamin C serum requires refrigeration; strong scent, high 23% concentration, no ferulic acid.

2025-07-17 Vitamin Reviews Categroy：Vitamin C Views：41

This K-Beauty vitamin C serum prevents oxidation with fridge storage, has an odd scent, and works well with retinoids. May switch to lower concentrations.

This review is from Amazon.com for product:

COSRX Pure Vitamin C 23% Serum with Vitamin E & Hyaluronic Acid, Brightening & Hydrating Facial Serum for Fine Lines, Uneven Skin Tone & Dull Skin, 0.7oz/20g, Korean Skin Care

K-Beauty Vitamin C Serum Review: Fridge Storage & Tuna Scent

(I reordered - so this will become a go-to product for me!)

I like the CosRx brand. It's one of my go-to brands along with Beauty of Joseon (such a gorgeous brand of skincare!, Belif (sometimes and some things), and Gangnam Glow, along with a few others. CosRX & BOJ are the two I have been reaching for more than any others, lately.

This vitamin C isn't L-ascorbic acid but it is ascorbic acid--although sometimes there is confusion there if they are the same or not.

The price like a lot of K-Beauty brands is very reasonable.

I keep mine in the fridge. I have had vitamin C oxidize and when it does it's a waste of money since it's no longer effective when it turns orange. The color of your C should be light, like, well, like very hydrated pee - sorry, that's all I can think of to describe it! :) When it begins to turn orange, you should not use it. So refrigeration, or maybe if you use it within 3 months it may be okay.

It does fizz when you open it. I've never had this happen with a serum. Kind of weird. As for the smell - well I have Parosmia from Covid a few years ago that I still have trouble with some scents and odors. I had a friend smell it and he said it smells like tuna, and that's what I thought - it smells like tuna smells to me with Parosmia. Not pleasant but it doesn't last. Also, keeping it in the fridge seems to make that smell not as bad, that or I'm used to it now.

I use my C in a very specific way: I only use it in the mornings. I first cleanse my face (I use BOJ ginseng oil based cleanser), and then I will tone it with either Belif milky toner, BOJ ginseng essence if I'm using that as a toner that day, or CoxRx centella asiatica toner. Then I go do something - take my dog out, have some coffee - anything that takes about 20 minutes for the toner to absorb and my skin to be dry. Then I apply my vitamin C. I then let the C absorb by checking my emails or looking on Amazon or whatever - for 15-20 minutes. Then I go on with the rest of my skincare - serums, moisturizer, SPF if I am going to be leaving the house. I like to let each step absorb but I don't necessarily go the full 15-20 with the serums and moisturizers as I do the C.

This does not irritate my skin. I did do a patch test as they advise. I put some on my inner arm, but I also put some along my right jawbone just on the bottom part of my cheek. I let that sit for hours until I knew it was okay.

However, it is 23% and in hindsight I wouldn't go above 20%, especially with my rosacea prone skin. 20% is plenty high enough. 10% is on the lower end. So 10-20% is the 'sweetspot.' Just because I"m not reacting now, doesn't meant my skin won't be mad later. I try to use my lower concentrate from another brand sometimes instead of this.

Vitamin C works well with and for my skin. I do like L-ascorbic acid products but really if you are using a retinoid (tretinoin) or some other stronger retinol, this products that aren't expensive work lovely.

Would I order again? Probably will not. But I'd like to find a K-Beauty vitamin c that has ferulic acid along with the c, as this one does not.

As with any skincare, you have to give it time. These things don't happen overnight. Consistency is key.

Vitamin Basics & Tips

Vitamin C serums, like the reviewed CosRx product, often use ascorbic acid (a form of L-ascorbic acid) for its antioxidant benefits. Stability is critical: exposure to light, heat, or air can cause oxidation, turning the serum orange and rendering it ineffective. Refrigeration slows this process, extending shelf life. The ideal concentration range is 10-20%—higher percentages (e.g., 23%) may irritate sensitive or rosacea-prone skin despite short-term tolerance.

Pairing vitamin C with ferulic acid enhances its stability and efficacy, a feature missing in this product. For users incorporating retinoids (like tretinoin), non-irritating vitamin C formulas are essential to avoid over-exfoliation. Application timing matters: apply to dry skin after toners, wait 15-20 minutes before layering other products to maximize absorption.

Daily use in morning routines is common, as vitamin C boosts UV protection when layered under sunscreen. However, its acidic nature requires gradual introduction—patch testing on the jaw or inner arm helps identify sensitivities. While K-Beauty brands prioritize affordability, selecting serums with complementary antioxidants (e.g., vitamin E) improves results for hyperpigmentation and collagen production.