OST C21.5 Serum Review

OST C21.5 Serum review

To kick off the Skincare Week on the blog, I’m going to start with a Korean skincare product; a serum that has garnered rave reviews from almost all the bloggers who have used it and one that I, too, was very very eager to try out. I’m talking about the OST C21.5 serum which is a Vitamin C serum.

OST C21.5 Serum review


I received the OST C21.5 around 3 and a half months ago and was so excited about trying it out, I went a bit overboard and started using it twice a day. Now, that isn’t really a problem, but I used it twice a day over the Mario Badescu Glycolic Acid toner. Perhaps the combination of an acid toner and potent vitamin C serum was a bit too much for my skin to handle and I got a sensitive reaction with the skin all around my mouth and chin becoming red, sore and peeling (read this post on how to deal with sensitive skin). So I stopped using both, the toner and the serum for a while till my skin became normal again and then slowly introduced both into my skincare regime.

When I restarted using the vitamin C serum, I used it every alternate nights slowly making it every night. Also, I don’t use the Glycolic toner along with this now; the toner is kept for alternate mornings. Here’s the OST C21.5 Serum review….

OST C21.5 Serum review


About the OST C21.5 Serum from Wishtrend

“The C21.5 is an improved version of Wishtrend’s immensely popular OST C20 serum. With an upgraded formula with more of the effects but less of the ingredients, the Pure Vitamin C21.5 serum has been transformed to have even greater hydration and absorption without the stickiness. It conditions and restores balance to replenish and retain moisture in the skin with the optimal 21.5% of pure Vitamin C. “

What’s the packaging like?

OST C21.5 Serum review

Nestled in a vibrant orange outer carton is an amber glass bottle that contains the Vitamin C serum. It also has a dropper that you replace the normal cap with once you open the bottle. Vitamin C is photo-sensitive and oxidises very fast when exposed to light which is why it is imperative to store it in  a dark bottle. This is one of the rare times when I haven’t disposed off the outer carton. You can see the condensation on the bottle in the picture and that is because I have kept the bottle in the refrigerator since the time it has arrived. When I had to take the pictures, I quickly took a few shots and put the bottle back in the fridge as soon as I could.

While the dark bottle is good for keeping the vitamin C in the serum stable, it certainly isn’t travel-friendly. And the fact that the serum should ideally be kept refrigerated itself means that I avoid taking it with me when I travel.

Who should use it? When to use it?

If you are facing pigmentation, blemishes, dull, dry and uneven skin, then the OST C21.5 serum is for you. Vitamin C is known to brighten the skin, helps in fading marks and pigmentation and helps increase hydration.

The recommended usage is both, morning and night,  after cleansing the skin and prepping it with toner. Based on my experience, however, I would advise you to not use it along with an acid toner. Personally, I prefer to use it directly after cleansing my skin only at night. Each person’s skin is different and you need to adjust the usage according to your skin’s requirements and tolerance levels.

Using a vitamin C serum does make the skin more photo-sensitive so you MUST make a good broad-spectrum sunscreen part of your morning skincare routine.


Hippophae Rhamnoides Water, Ascorbic Acid, Sodium Lactate, 1,2-Hexanediol, Sodium Hyaluronate, Panthenol, Cassia Obtusifolia Seed Extract, Allantoin, Xanthan Gum, Ethyl Hexanediol

The Good

OST C21.5 Serum review

True to claims, the serum does have a very light, watery texture. It has a faint fragrance which doesn’t linger long and is definitely not sticky. It also helps in keeping the skin hydrated but that could also be a result of the other skincare products I am using along with this, all of which are hydrating ones.

I had two huge pimples (one on each cheek) before I went on my holiday and this serum is helping those marks fade well. No new breakouts since I have started using this serum thankfully (touchwood). Despite getting really tanned during my trip, my skin doesn’t look dull; this serum makes my skin appear brighter and radiant.

The best part? No parabens,  no mineral oil, no silicones, no phthalates,  no phenoxyethanol!

The Not So Good?

Though this serum claims to be mild enough for sensitive skins, it does tingle a bit. If your skin is very sensitive then you would need to start out slowly with this or you might get a reaction like I did.

While the serum itself doesn’t feel sticky, when I layer another serum or cream over it, it does feel sticky when I massage it in. I try to keep a gap of a few minutes between both the applications so that the Vitamin C serum gets absorbed well into the skin but still anything else I put on top feels sticky.


The OST C21.5 is currently available at a discounted price of US$ 24.99 (approximately ₹1,600) on Wishtrend.com with free shipping.

To Sum It Up

 A wonderful, lightweight serum that absorbs quickly into the skin and does help fade the acne marks. It also hydrates the skin well without letting it get oily and gives it a brighter look. No breakouts either. Just start out easy with it and don’t go overboard the way I did. Learn from my experience 🙂

9 Replies to “OST C21.5 Serum Review”

  1. I have got darkspots in my cheecks areas can i use this??

  2. I have horrible dark circle .Is this serum help me

  3. You said it need to be store in the fridge, to keep it cool, but I just order my, and it the summer months…..would that be fine? And I have oily or sensitive(I think) skin, is it fine I use this as well?

    1. It’s written on the outer box that it needs to be refrigerated. Keep it in the fridge as soon as you get it and take it out only when you want to apply. That’s what I do and it’s fine. No oxidation at all.

  4. Raazia najam says: Reply

    Serum avaible in UK .

  5. Gowthami@BeautyFrontline says: Reply

    Looks super light!

    1. It does have a lovely light texture.

  6. Raazia najam says: Reply

    Can l use this serum .l am 24 year old . Where l buy this ?

    1. If you have dull, uneven skintone with acne/pigmentation marks, you can give this a try. It is available on the wishtrend website. The link is up in the review.

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