Skin & Tonics : Skincare Guides & Product Reviews

Skincare guides & product reviews for hydration lovers & the moisture barrier obsessed

O.S.T. Original Pure Vitamin C20 Serum Review

I was really excited to finally get my hands on a bottle of O.S.T. Vitamin C20 Serum. It’s been on my wish list for a long time. I’m a big fan of Vitamin C as a skincare ingredient in general, but stopped using it last year when I started using tretinoin (generic Retin-A). It’s generally advised not to mix tretinoin and Vitamin C in a single routine, though, if your skin isn’t sensitive (and you’re not spending a lot of time outdoors), it can be okay to use Vitamin C in the morning and tretinoin at night. It took a while for my skin to get used to the tretinoin, and my skin was very sensitive during that time; I just didn’t think my face could handle both. My skin is now used to the tretinoin, and I just switched to the micro-gel version (which I find to be much gentler), so when I had the opportunity to try this serum, I said, “Get on my FACE, Vitamin C!” Okay, I didn’t say that. But I thought it, and I still think it every morning, as I’m applying this serum.

O.S.T. Original Pure Vitamin C20 Serum

What is it?

O.S.T. Original Pure Vitamin C20 Serum ($25) is a Vitamin C powered serum that claims to exfoliate, brighten skin, fade acne scars/post-inflammatory hyperpigmentation (PIH), and remove blackheads.

O.S.T. Original Pure Vitamin C20 Serum

Water, Ascorbic Acid, Ethanol, Sodium Lactate, Butylene Glycol, Glucose, Camellia Sinensis Leaf Extract, Rosa Davurica Bud Extract, Carthamus Tinctorius (Safflower) Extract, PEG-60 Hydrogenated Castor Oil, Sodium Hyaluronate, BIS-PEG-18 Methyl Esther Dimethyl Silane, Diethoxyethyl Succinate, Ammonium Acryloyldimethyltaurate/VP Copolymer, Xanthan, PEG-180, Gluconolactone, Beta-Glucan, Citrus Aurantium Dulcis (Orange) Oil, Zinc PCA, Panthenol, Niacinamide, Glycerin, Tocopherylacetate, Lecithin, Caprylic/Capric Triglyceride, Ubiquinone, Diisopropyladipate, Phenoxyethanol, Methylparaben

The ingredient list looks okay at first glance, as this serum does contain a multitude of good skincare ingredients. There are also some things about this ingredient list that I find confusing, but I’ll get to that in just a minute. First, the highlights:

Ascorbic Acid – Ascorbic acid is the source of Vitamin C in this serum, and it accounts for 20% of the serum. As a general rule, you want at least 10% for an effective formula, 15% is better, and 20% is pretty great. Topical Vitamin C has been scientifically proven as an effective topical treatment for a variety of skin conditions, including acne, reduction in photodamage, fading of scars, and strengthening the skin’s barrier function. It also promotes collagen production, and is often marketed as an anti-aging ingredient for this reason.

Unfortunately, Vitamin C in general is not very shelf stable. It’s extremely sensitive to light and oxygen; overexposure to either one of those things will cause it to oxidize rapidly, at which point it loses its efficacy. This is why it’s important for Vitamin C to be packaged in dark colored or opaque bottles – a clear bottle would render the product ineffective fairly quickly. It’s also important to use up a Vitamin C product within a a reasonably short span of time – 3 months is a good rule of thumb, but if your Vitamin C product darkens at any point, it’s time to stop using it. A darker product means it has oxidized.

There are many different sources of Vitamin C; Ascorbic Acid (which also happens to be an AHA) only represents one of them. Unfortunately, it’s not the best choice to be used topically. It’s effective, but it is a little less stable, and it is more likely to cause irritation than other C sources such as C-ester or magnesium ascorbyl phosphate (MAP).

If you’re interested in reading just a small sampling of the scientific studies surrounding Vitamin C as a skincare ingredient, here are some good places to start:

Topical Ascorbic Acid on Photoaged Skin
Improved Scar Appearance with Combined Use of Silicone Gel and Vitamin C for Asian Patients
Vitamin C in Dermatology

O.S.T. Original Pure Vitamin C20 Serum

Sodium Lactate – Sodium Lactate is a sodium salt derived from Lactic acid. It’s a highly effective antimicrobial agent . In fact, it’s often used as a preservative in meat and poultry products for precisely this reason. As a skincare ingredient, it also has exfoliating properties and works well as a pH adjuster.

Camellia Sinensis Leaf Extract – Better known as Green Tea Extract, this ingredient is a highly effective antioxidant and anti-inflammatory ingredient.

Sodium Hyaluronate – Often referred to as hyaluronic acid, this ingredient is able to hold up 1,000 times its weight in water. This humectant also does a great job attracting and maintaining water in the skin, and promotes blood circulation and nutrient absorption.

Niacinamide – This is a cell-communicating, anti-inflammatory ingredient that has been proven in numerous studies to increase barrier function and ceramide levels, and lightens hyperpigmentation. It’s one of my all time favorite actives!

However, I am a bit confused about Niacinamide’s presence in this formula, as it is typically known to be incompatible with Vitamin C, especially in the form of Ascorbic Acid as it appears in this serum. Niacinamide and Vitamin C cancel each other out when mixed with one another in water-based solutions – which is what this serum is. Because Niacinamide is so low on the list of active ingredients in this formula, I’m guessing it’s not present enough to cancel out the efficacy of the Ascorbic Acid, but I am wondering what its role is in this serum. If any cosmetic formulators happen to be reading this and can shed some light on why Niacinamide is included in this formula, I’d love your insight!

O.S.T. Original Pure Vitamin C20 Serum

Ubiquinone – Better known as CoQ10, Ubiquinone is an antioxidant that can help increase collagen production when present in large enough amounts. Ubiquinone is pretty low on the ingredient list in this particular formula, however, so once again, I find myself asking why it’s been included.

It’s worth mentioning that this formula also contains alcohol (which appears as “Ethanol” in the ingredient list). The alcohol is the only major red flag in the O.S.T. Vitamin C20 Serum according to COSDNA, where the ingredient ranks a 3 out of 5 as a potential irritant. I’ve mentioned here before that there are a large number of people who believe that alcohol is harmful to the skin in any amount and in any formula. There is also a line of thought that when included in a well-formulated product, it is a beneficial ingredient because it increases the absorption of other skin-healthy ingredients. Based on the research available, which is best summed up in this FutureDerm article, I’m personally inclined to fall into the “alcohol can be good in a well-formulated product” side of the great debate.


The O.S.T. Original Pure Vitamin C20 Serum arrives in a well-sealed, amber glass bottle. The dark colored glass is a good choice for helping to prevent product oxidation. It comes with a glass dropper cap, which is packaged separately to prevent it from breaking during shipping. I would have preferred to see this product in an airless pump to prevent air exposure, but a dropper is fine – it would be my second choice.

O.S.T. Original Pure Vitamin C20 Serum


O.S.T. Original Pure Vitamin C20 Serum

This serum smells delightfully like fresh oranges.

Before I get into my application method, I’d like to point out that the O.S.T. Vitamin C20 Serum really is designed to be used at night. The primary reason for this is its Ascorbic Acid content, which is easily broken down by UV rays. That said, I use this product during the day because I’m a nightly Tretinoin user, and the two products aren’t compatible. However, I am very vigilant about wearing sunscreen, and most days I get very little sun exposure – 22 minutes total for my drive to and from work. I skipped this serum on a couple of occasions when I knew I would be outside or in the car for a while.

As for my application method, I apply this serum as soon as I dry my face after cleansing in the morning. In a typical Asian skincare routine, this would actually be the serum step, which comes after the toner, but back when I was using the Perricone MD Vitamin C product, I applied my C first thing after cleansing. That worked well for me, so I decided to use this in a similar manner. I follow up with my facial oil, my sunscreen, an essence, and my moisturizer.

O.S.T. Original Pure Vitamin C20 Serum


O.S.T. Original Pure Vitamin C20 Serum

Before trying this serum, I read a few blog reviews that stated this serum dries with a sticky finish. If you apply this serum on its own and don’t apply any additional skincare products afterward, that is 100% true. This serum glides on during application, but it does feel sticky to the touch once it’s dry. However, there is never a situation when I’m applying this serum on its own – well, except for the instance when I did it for the purpose of learning if it really is sticky. Once I apply my subsequent skincare products, there is absolutely no trace of stickiness.

Also worth mentioning is that the O.S.T. Vitamin C20 Serum does tingle a bit just after application. I can’t tell if it’s the alcohol, the Ascorbic Acid, or a combination of both that’s causing the sensation, but it’s definitely there. It’s not unbearable – in fact, I wouldn’t even call it painful. It’s just slightly uncomfortable for a minute or so after application.


There are a few things I wish I could change about this serum: I wish it didn’t contain Niacinamide because of its incompatibility with Ascorbic Acid, and I wish it didn’t cause any sensation when I apply it. If I had my way, I would also probably forego the alcohol in this formula, even though I’m not entirely averse to alcohol as an ingredient in the right product.

All that said, my results from using the O.S.T. have been spectacular! When I began using this serum, I had some very visible hyperpigmentation spots on my right cheek that had been lingering for weeks with little to no fading. After the second week of using the O.S.T. Vitamin C20 Serum, I noticed they had faded dramatically, and by day 28, they were almost gone. My overall complexion also looked visibly brighter after about a week of use, and my overall skin texture appears smoother now than it did a month ago, especially in my nose area. I’m fortunate not to have very large pores or any blackheads, so I am unable to comment on whether this serum helps with either of those issues.

O.S.T. Original Pure Vitamin C20 Serum

Day 1 of using the O.S.T. Original Pure Vitamin C20 Serum

O.S.T. Original Pure Vitamin C20 Serum

Day 28 of using O.S.T. Original Pure Vitamin C20 Serum


In spite of the tingling sensation I experience when applying this serum, the O.S.T. Vitamin C20 Serum did not cause me any visible skin irritation aside from some very mild peeling during my first couple of weeks using this product (the ascorbic acid is exfoliating, after all). When the peeling did occur, it happened at the end of the day, which leads to be believe I probably wouldn’t have noticed it as much had I been using this product in the evening as directed – the dead skin would have washed away with my morning facial cleanse.

O.S.T. Original Pure Vitamin C20 Serum

I’ve been using this serum for going on 33 days now, and definitely plan to finish the bottle. I love the results I’ve been getting from it, and I’m looking forward to seeing my hyperpigmentation spots completely disappear. I would definitely consider purchasing the O.S.T. Original Pure Vitamin C20 Serum again, especially since it’s priced affordably at $25 retail. I will probably experiment with some other serums first though, now that I’m back on the Vitamin C train!

– Highly effective against acne marks/post-inflammatory hyperpigmentation (PIH)
– Improves skin texture
– Effectively brightens skin tone
– Packaged in a dark bottle to delay product oxidation
– Smells like fresh oranges
– Contains a high amount of Vitamin C

– Tingles a bit during application
– Contains a couple of questionable ingredients
– The Vitamin C source is just okay for topical application

Skin & Tonics Rating:

Performance: 5/5 – Very effectively fades acne marks, improves skin texture, and brightens as promised

Quality: 3/5 – The packaging is okay, but would be better as an airless pump. Overall ingredient list could use some improvement.

Value: 5/5 – Very well priced for such a highly effective product

Overall: 4.4/5

Where to buy

The O.S.T. Original Pure Vitamin C20 Serum is available from Wishtrend. It normally retails for $25, but right now it’s on sale for $20, so it’s a great time to pick this up!


This article features a press sample that was sent to me for my unbiased consideration. Any opinion expressed is 100% my own. For more information about my review policies, see my full disclosure.

This post contains affiliate links. Shopping these links helps support this site. Full disclosure.

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86 comments onO.S.T. Original Pure Vitamin C20 Serum Review

  1. I Just Got the Vitamin C from Ciracle.. And I haven´t seen a big difference..I thinks It´s ok but not Time I would try O.S.T..:D

    • Kerry

      Aw man. That’s disappointing about the Ciracle! How long have you been using it? Does it smell like oranges too? The ingredient list for that one looks very, very similar to the O.S.T. list. If the Ciracle let you down, you might find the O.S.T. underwhelming as well.

  2. That is some amazing result right there! Definitely interested in trying products w/ vitamin C now…
    And, I learned something new today about the ingredients! 😛

  3. Your before and after pictures are gold! I’m definitely going to give this a try, since I have some stubborn hyper pigmentation. And I love the smell of citrus fruits lol.

    • Kerry

      I think it’s definitely worth a shot if you have hyperpigmentation! I am obviously very happy with my results. I’d love to know how it works out for you if you try it!

  4. This thing works great! i wonder if it will works on my sun damage pigmentation..
    btw, what’s your skincare routine now?

    • Kerry

      Hi Rev! At the moment I’m experimenting with a variety of Shea Terra Organics products, but my baseline routine is still Benton along with my Argan and Maracuja oils.

      If you’re looking to lighten up your hyperpigmentation, I think this product is definitely worth a try!

  5. I have been lurking your blog for this review and holy s***balls I love the results it gave you. I gave the serum a second try and I seriously don’t know what happened. I think it did give me little bumps on the side of my cheeks. I’m starting to think I have sensitive skin. Going to take another week or 2 off for my skin to calm down before giving it another try for my final verdict.

    • Kerry

      You might be sensitive to this serum – it certainly isn’t the gentlest formula, in my opinion. As much as I love the results I’m getting from this serum, I’ll be seeking a gentler formula for my next Vitamin C experiment. Perhaps you’d have better luck with product that uses C-ester or MAP as its C source instead of straight Ascorbic Acid? That’s what I’ll be looking for in the next product I try. 🙂

      • Hi Kerry,

        Do you have your eye on any specific MAP Vitamin C serums?

        This ingredient list looked intriguing to me:
        Distilled water, Hyaluronic Acid (15%), Vitamin C [MAP] 15%, Grape seed Extract, Green Tea Extract, [Bees Wax, HE-Cellulose, Polyglyceryl Oleate], Pure Rice bran Oil, Pure Argan Oil, Vitamin E, Matrixyl 3000, Silk Amino Acids, Honey Extract, EDTA Tetrasodium, Silk Powder, Germall, Potassium, Allantoin, Aloe-vera Leaf Extract

        This is the order link I used (link gives 10% off):–Vitamin-C-15-ASDM-Beverly-Hills_p_50.html?utm_source=shopalize&utm_medium=social&utm_campaign=purchase_20_per_off_sale_referral&_shref=BVgla&_shw=ppw&_srv=facebook

        I’m really curious how it (a MAP formula) compares to Ascorbic Acid on my sensitive skin.

        The last one I used was Ascorbic Acid (Paula’s Choice RESIST c15) and I really liked the feel of the formula, as well as found it doubled to be the most effective treatment to lessen the appearance of a scar on my hand; worked better than her scar serum for me. I also found it was easier to tolerate in between Clinique Redness Relief Cleanser and moisturizer designed for sensitive/red skin.

        I wish Ascorbic Acid was a more stable form of Vitamin C; then I’d be less concerned about buying it and taking my time using it up. It took me about four months to use up this three month supply, which I thought wasn’t too bad considering. Sometimes I’d spot treat on my face.

        Do you remember if you did anything specific with the rest of your routine while using OST Vitamin C serum to try to lessen sensitivity/potential irritation?

        • Kerry

          I definitely want to try a MAP C serum! As soon as I’m done with the Paula’s Choice one I’m trying right now, I plan on picking one up. The ingredient list for the one you linked does look good! And the price isn’t bad either. I’d definitely consider that one.

          When I used the OST serum, I did find it to be mildly irritating, especially at first. My moisturizer helped with alleviating the irritation a lot during the OST. At the moment I am trying out a Paula’s Choice Clinical Advanced Redness Relief with my current AHA, and find that it helps a lot with any redness I experience from sensitivity. I think it would also help with the OST sensitivity, but I haven’t tried the two together!

          I got your email, by the way! I plan to respond as soon as I get enough time to myself to write more than a couple of sentences. 🙂

          • Which moisturizer did you use after the OST 20% Vitamin C Serum? Are you using the Clinical Advanced Redness Relief as the step directly after the Vitamin C Serum? That’s a neat idea. Thanks for your nice message 🙂

  6. I’ve been thinking of trying a vitamin C serum so this was very helpful, thank you. Do you use other products with Niacinamide? I had a tingling/temporary redness reaction to a product I used with Niacinamide high up in the ingredients list, so I wonder if that could be related to the tingling. I know that when you eat an excess of Niacin it causes a tingling/flushing reaction (which I have unfortunately experienced firsthand, lol)

    • Kerry

      Nah, I haven’t been using any Niacinamide products with this serum. I love Niacinamide as an active though – it’s in a lot of my favorite products, and I’ve never had a reaction to it. I remember feeling some sensation (though not exactly the same as this one) back when I was using the Perricone MD Vitamin C-Ester. I’m thinking the tingling may be something to do with high concentrations of Vitamin C in general. It definitely requires further investigation!

      • First of all thanx for the review Kerr!- it’s amazing, like always! I’ve never tried this particular product, but I love Vit C in skin care- it works! And speaking about Niacynamid (Vit B3) is very good ingredient (pores shrinking, anti-oxidation, stimulating hyaluronic acid production anti acne, helpful in rosacea, whitening), but unfortunately is proven, it can cause some irritations if to high concentrated and if used on very sensitive skin- so it’s not for everybody…

  7. Once again, you’ve blown me away with your ingredient knowledge and interactions. Great review and great results. You remind me I’ve gotta start using a C serum. My routine is very similar to yours as I use Benton essence along with the same oils. But I’m almost twice your age and I have more hyperpigmentation to deal with than you. Thanks again for the great review! I’m impatiently waiting for benton to come out with their SPF!

    • Kerry

      You and me both, Angel! I wish they’d come out with that sunscreen soon!

      If you’ve got hyperpigmentation issues, a C serum is definitely worth a shot. I have a few products in my arsenal that help a lot with hyperpigmentation, but this C serum was downright impressive on that front.

  8. I mix my own vitamin c serum weekly and has seen great result. My skin is plumper, and even some minor rolling scars seem to look more shallow. 🙂
    I think vitamin c is great and ascorbic acid is actually the best one for collagen but it only work on 60% of the population. I think the tingling you’re are experiencing means either it working or that it’s too strong for you. If the sting is too unbearable then maybe you should consider a lower dosage?

    • Kerry

      Hey Annie! Any chance you’d share your Vitamin C recipe with us?

      • I’m embarrass to share because it’s really simple. Just ascorbic acid + water + glycerin + aloe vera gel. Everything is in tsp
        5% = 1/2tsp a.a+ 1/2tsp glycerin + 5tsp water + 3tsp aloe vera gel =50ml
        10%=1/2tsp a.a+ 1/2tsp glycerin + 3tsp water + 1tsp aloe vera gel =25ml
        15%=1/2tsp a.a+ 1/2tsp glycerin + 3/2tsp water + 1/2tsp aloe vera gel = 15ml (this one is roughly 16.67% a.a though)
        20%=1/2tsp a.a+ 1/2tsp glycerin + 1tsp water + 1/2tsp aloe vera gel = 12.5 ml

        Of course you can add other goodies. I read that adding 1% vitamin e in will help boost sun protection as vitamin c and e recycle each other. I am not terribly accurate, but I make mine weekly and keep it in the fridge to hopefully slow down the reaction and second, to slow down bacteria grow.
        Sometime instead of water, I used a simple toner instead because they have preservatives in it. Im not too terribly against preservatives because I rather have some of them than to have a bacteria infested product. Good luck!

  9. Thanks for that recipe Annie! I’m making this tomorrow. It’s much simpler than the current recipe I have. I finally found natural, alcohol free witch hazel. I think I’ll try that in place of the water.

  10. Hey Kerry! I have an unrelated question (although I’m definitely going to pick up this serum to try and get rid of my facial scarring).

    I stumbled on your blog months ago, obsessively read through it all, and then I got the full Benton line to try out and it’s been working great for my skin (which is oily and very acne-prone). My mother loved my results and also got Benton, but since we have different skin types and issue she’s not sure what products she should be using.

    I was wondering what products you would recommend for a mid-50’s woman with dry/normal skin, whose primary concerns are wrinkles, lack of glow, large pores, dryness, and papery skin? If you know of anything off the top of your head, that would be extremely appreciated!

  11. Hi Kerry!

    Thanks for the product review. How do you incorporate the Vitamin C20 into your skincare routine with the Benton Aloe & Snail?

    • That’s exactly what I was wondering. I’d like to try something similar to Kerry’s routine as well as this serum, but there doesn’t seem to be a “serum step” in the routine.

      When you you apply the serum?

      • Kerry

        Hi Ida! If I were using this with the Benton products, I would use this serum in place of the Benton Snail Bee Essence, after the Benton Aloe BHA Toner. The Benton Snail Bee Essence is the serum step in that routine, despite the confusing product name. However, there’s nothing stopping you from using this in addition to the Benton Snail Bee Essence – just be sure to use the Vitamin C serum first.

        • If you had to choose between the Benton Snail Bee Essence and a vitamin C serum, which would you pick? I’m kind of stuck and I don’t know which one is going to be better.

  12. Great Review! I’ve been using the OST Vitamin C serum for a couple months now and I’m seeing amazing results including brightening, fading of dark marks, and overall better skin texture. The serum provides me with better results when compared to the very expensive Phyto-C serums I’ve used. The only drawback is that I live in San Francisco, CA, USA and it can take several weeks for a shipment. It’s actually been about a month now, and I’m completely out of the serum, and I’m still waiting for my shipment from Wishtrend to arrive 🙁 I can imagine, it’s taking longer then usual due to the holidays. Other then that, the product is wonderful!

    • Kerry

      Oh geez, Carolina! Somehow I missed this comment – my apologies! Anyway, I hope by now your serum has arrived! It’s good to know that this has performed better for you than the more expensive serums. Thanks so much for sharing!

  13. Wow what a really good review!! So complete! I also bought it from wishtrend will come like in 4 days.. waiting!! Hey could you review caolion sensitive bb cream? I have read great reviews from it!!!! Would like to see ur personal opinion! Have great year!!

    • Kerry

      Hi Piu! I’m so glad you enjoyed the review! I will have to take a look at the Caolion BB Cream. I am a sucker for a skin care product with the word “sensitive” in the name!

  14. I dont know if you know this site but it is a non profit organization that work the same way like COSDNA, actually i think this place is better….the site is

    • Kerry

      Hi Mary! You know, I used to love EWG years ago, but they are sadly no longer a reliable resource. EWG now has has a lot of political ties, and has even had its non-profit status called into question. Additionally, over half of their ingredient lists are incorrect, and they consistently misuse, misread, and misrepresent data. I think EWG is useful as a starting point for researching individual ingredients, but overall, not a very reliable source, unfortunately. 🙁

  15. Hi Kerry.
    I discovered Korean cosmetics and skincare products last year, started with the BB creams and before I realized, I was addicted.

    While searching for more info, I found your blog and now I’m a huge fan, I like the way you write the articles and especially your researches and I just want to thank you because you’re doing a great job.

    I suffer from rosacea combined with oily skin and I have to admit you inspired me to purchase a lot of the products you have reviewed, hoping to improve my skin condition.
    I have recently tried the Benton BHA, essence and cream and I love them. I also have Missha’s first essence, the Night repair, the OST serum and I even purchased products from Paula’s choice and Sulhwasoo.

    I am still new with all the asian skincare routine and this is why I wanted to ask you if you think Missha’s first essence and night repair can be combined with Benton products and the OST serum.
    I apply the First essence right after cleansing my face, followed by the Benton BHA, my 3rd step is Paula’s choice anti-redness exfoliant, then the OST serum (at night), after that I use the Missha’s night repair, followed by Benton’s snail essence, I apply after Benton’s aloe gel and in the end Benton’s cream. I don’t know if it is too much, though.
    My face feels moisturized, my skin smoother and although the redness has not miraculously vanished (it would have been too good to be true) I do believe the situation is somewhat better.

    I dream for the day I won’t need a BB cream or a foundation to go out, but meanwhile I keep trying products that can help my red face.

    Once again, thank you for your blog.

    • Kerry

      Hi Eva! I don’t think that sounds like too much at all – I often go through phases when I’m applying as least as many products! If your skin feels and looks good and you don’t mind the long ritual (I personally love a long skin care ritual), you should be fine. I will say that for me, applying the Paula’s Choice Exfoliant and the OST serum in the same routine would be a bit much for my skin – I’d wind up with flaking and an increase in sensitivity. I would personally opt to use the Paula’s Choice Exfoliant in the morning and the OST serum in the evening. But if you aren’t having any issues, there is no reason you can’t use the them together. 🙂

  16. Hi Kerry,

    your new follower heree (:
    You’re amazing btw. I just have a question. I have this serum, Paula Choice’s 2% BHA liquid exfoliant, and Benton BHA toner, how do i use them? Can I use them together? or should I use the Vit C first, run out of it then use the PC exfoliant? do you know the pH level of OST Vit C? I don’t wanna mix it with Benton Toner since it might cancel out how effective they are.

    • Cara

      I am also interested in knowing the pH levels of this product. Ascorbic Acid is only stable if it’s in a pH level lower than 3.5. I’m curious to know where this falls.

  17. Hello!
    I’m totally sold! I wanna get my hands on the OST Vit C. DO you know if there is any shops in Korea that sells? I’ll be there in a few days time and are keen to get it. Thank you!

  18. you should try out the c15 from paula’s choice its amazing! they have a 2 week sample for 9 bucks 🙂

    • Kerry

      Hi Joan! I am actually in the process of trying that one out now! I should have a review up in a few weeks. 🙂

  19. Kerry, U are the best! When I look for sth. it’s always U who knows the answer! Thanx girl! 🙂

  20. Angela

    HI, I was wondering if you’re still using the OST VitC20? I was thinking of purchasing it but wanted to know your thoughts – this far after your initial review. Thanks.

  21. Phi

    Hi Kerry, I started using Korean skincare products a few months ago and am still learning a ton. Your site and reviews have been so helpful!!

    Question for you – I have been using Su:m37’s Secret Programming Essence which I found to be wonderful for my dry, acne-prone with PIH skin, but I know it contains Niacinamide. I also started using OST Vitamin C and am wondering how to make sure they’re both being used effectively and to get the most out of their ingredients. Do you have advice for how /when to use them? Thank you!!

  22. ayu

    is it okay to use this serum with benton snail bee cream? will the result still same? since both of them having a difference concern an ingredients, thankyouu

  23. That before and after is amazing!

  24. Anna

    Amazing review and astounding results! You’ve been very helpful to me lately! I recently purchased this serum as well as missha first treatment essence. Since the latter contains niacinamide as it’s 4-5th ingredient, do you think I can still use it in conjunction with this serum or will I render both products ineffective? I’d appreciate some tips/advice! Have a great day!! 🙂

  25. Wendy

    Hi there . I’m just wondering if it’s okay to use this product while I’m on accutane . My derma said that my face is very sensitive to the sun and does this product make u more sensitive ? Thanks in advance

    • Kerry

      Hi Wendy! I would definitely advise asking your derm if it’s okay to use an L-ascorbic acid based Vitamin C serum while on Accutane. L-ascorbic acid can increase sun sensitivity. I hope that helps! 🙂

  26. I’m surprised to not see any comment that may point out the irritation may very well be due to the inclusion of another known irritant along with the alcohol, citrus oil. There are so many good Vit C choices available currently that I would have passed on this one simply due to ethanol as the third ingredient. Couple that with citrus oil and this is a pass. Thanks for trying it out for others.

  27. I had a quick question — I use a vitamin C serum similar to this (Obagi 20%, Japan version), and recently I picked up the Missha First Treatment Essence. I use both during the day, but which should come first? Thank you for de-mystifying Korean skin care for us all 🙂

    • Anna

      Hi Grace, although this question was directed at Kerry, I had asked her this same question. She had told me to just use the OST first and allow the ph to neutralize on its own! Once you apply a product, the product’s ph neutralizes completely in about 30 mins. Most people don’t have 30 mins so I only waited that long at night. (I did 10 mins in the morning which still worked just as well!) So I do OST – 30 mins – Missha FTE – few seconds for it to sink in – eye cream and emulsion! 🙂 Onviously you can moisturize more if your skin needs it but mine does not. I have severe dark spots from acne and doing this has helped me IMMENSELY! I hope this has helped and shed some light on your inquiries. Feel free to ask again if you need something else. 🙂

  28. Melody

    Right now, wishtrend is having a sale on this product…. Three for $34! What do you think? I’m worried that given that the product isn’t as shelf stable, it might not be smart to buy that many at once? But it’s a great deal. 🙂

    • Kerry

      Oh wow, that’s a great deal Melody! At that price, I would definitely take advantage of it. Even if you couldn’t make it through the 3rd bottle before it oxidized it would be a steal! And you could always keep the spare bottles in the fridge so they last longer. 🙂

  29. Anna

    I wonder if theydo this deal to get rid of over stock before getting a new batch? I did a two for one deal on this serum about a week ago. Curiously, how many drops do you guys use at one time? Also how long does it take you guys to finish one bottle? (Either with or without the fridge.) without putting it in the fridge and likely using way too much at once, I went through a bottle in about 5-6 weeks >_<

  30. Michelle

    Since this serum has exfoliating properties, should I stop using other exfoliators in my routine if I purchase this? And do you think this serum can be used every night or would that be too much because of over-exfoliation? Thanks!

    • Kerry

      Hi Michelle! I personally didn’t stop my other exfoliators. The exfoliating properties of Vitamin C are not as strong as those associated with AHAs or BHAs. Some people might find using both irritating though, especially if they don’t have a very high tolerance for acids yet. I’m fortunate that I don’t have that issue, but if I had to give up one – I’d probably give up Vitamin C, actually. I like the exfoliation I get from AHAs more, and I can always get my antioxidants in a different, gentler form if needed. 🙂

  31. Gee


    I have been obsessing over your beautiful blog and am slightly confused over two points.

    1) should I apply my O.S.T Vit C serum onto post-cleaned but otherwise naked skin or after using Paula’s Choice 2 percent BHA liquid?

    2) after applying the O.S.T serum should I go straight to face oil then moisturizer whilst skipping the hydrating toner? I can’t work out where to add extra moisture in this routine.

    Thank you so, so much!


  32. Christine

    How long did your bottle last? I just started using the serum almost a week ago and I already see a bit of a difference with my skin. I definitely plan on repurchasing it and I would like to order the serum so that it arrives when I’m close to being done with my current bottle.

  33. zula

    hi skin and tonics I love ur review and I was wondering if I can use OST vitamin c serum under my eyes?i want to brighten my skin but scared that only my eye area will be dark if I avoid using it under the eyes

  34. Mindy

    Hi Kerry! They have recently launched the “advanced” version – C20 Pure Vitamin C21.5 Advanced Serum with no artificial ingredients or irritants. It sounds good to me and I really want to try it but I am not sure if 21.5% is okay for the skin? This will be my first Vitamin C serum and I don’t really know much about the optimum amount for Vitamin C so I am worried that it will be too harsh on my skin. =/

    • Molly


      I was going to ask the exact same thing! I am wondering if the new C21.5 Advanced acts in the same way as the C20. The results of the original C20 look incredible, so I would love to check it out, but now I’m wondering if it would be better to buy the ‘improved’ version.

      Kerry, it says that the Niacinamide has been taken out of the new formula, which maybe improves the efficacy of the serum? All the other new ingredients look good too! Also, would the higher concentration of Ascorbic Acid mean it would be more effective, even when applied topically?

      Here is a link to the new formula on Wishtrend:

      Thanks for the great review! Super helpful 🙂

  35. Rizka

    I’ve been trying this for almost two months after I kept hearing a lot of rave reviews about it. But unfortunately this serum doesn’t work for me, it actually break me out. So sad because i really want it to work 🙁

  36. Uyen Vuong

    This is such a thorough and informative review. It helps me a lot in researching on the right vitamin c serum for my sensitive skin. I really appreciate your dedicated efforts in writing your reviews.

  37. Jean

    Hi! Thanks for such great review! I’m a newbie when it comes to such detailed skincare. Just want to ask, is c20 alone enough to be used as an essence/serum step? I’m contemplating between missha full treatment essence vs this c20. Can u give me some advice? Thank you!:)

    • Kerry

      Jean, you could use both of those in your routine if you wanted to – but if you were only going to choose one, I would personally go for the C20. And yes, it’s just fine to be used as your only serum step. I consider the Missha Essence to be more of a hydrating toner-like product despite the word “essence” in the name! 🙂

  38. zula

    hii first of all thank you for your amazing reviews and product recommendations, can i use Vitamin C serum while using hydroquinone? thanks

  39. Mizu

    Hi Kerry! I was just about to purchase a bottle of this myself, but then I saw OST Pure Vitamin C21.5 Advanced Serum (Upgrade) and was wondering if you’ve seen it before/have tried it out. It has MUCH less ingredients, but also some that aren’t in the Original. Here are the ingredients in order (

    Hippophae Rhamnoides Water (70%),
    Ascorbic Acid (21.5%),
    Sodium Lactate,
    Sodium Hyaluronate,
    Cassia Obtusifolia Seed Extract,
    Xanthan Gum,
    Ethyl Hexanediol

    The 21.5% ascorbic acid sounds great but I’m not knowledgeable enough to understand the efficacy of the other ingredients. I would love your input on this and if you could make a recommendation between these two for me! My skin is just about everything; oily, acne-prone, sensitive (extremely sensitive as of late), some dry patches with flakiness, and rosacea. Yup, my face is a mess.

  40. seppinator1111

    Hi Kerry,
    Thanks for the great article! I am just about to start using my C20 that I got a couple weeks ago. I’ve been carefully reading about skin ph and product layering, because its a lot to tackle and understand. I read somewhere that refrigerating the C20 prolongs the shelf life (as its cold and dark in there), and then I read elsewhere that refrigerating products has no benefits. Do you have an opinion? I am approaching a warm and humid summer in NYC, in an apartment with no central air, so I’m concerned about this, and other, face products.

  41. Zula

    Hi Kerry,ok first of all your blog is amazing,it totally helped me to improve my skin and find amazing products in sea of millions of beauty products of today and helped me to save money too.I have a question I recently bought Laneige White Renew essence and do I have to store it in fridge? I really love your blog good luck 🙂

  42. Salma

    Hi, I just bought this serum after reading about your experience with it. 🙂
    I have one urgent question: do you change out the bottle cap with the dropper permanently upon arrival? I tried and so much product overflowed! It doesn’t make sense…am i supposed to keep the dropper separate and wash and dry it before each use??

  43. Nong Sa

    Question! Could you apply this after applying P50 in the morning?

    Thank you!

  44. Sarah

    Hi there, can I use it if I’m 21 or are vitamin C serums meant for the mid 20s and above? I’m afraid of skin peeling

  45. […] Skin & Tonics – this C20 review has scientific analysis, before & after shots, and a detailed rating–go there to get your science fix […]

  46. Courtney

    Hello! I am new to the Asian skincare routine (so new, in fact, my first batch of new products from Wishtrend hasn’t arrived and I am anxiously awaiting some Prime deliveries tomorrow!) and have been loving this blog! I have purchased the advanced version of this serum as well a COSRX BHA treatment. What are the guidelines for applying two products like this? Based on some things I have read, to get maximum benefit, I should add wait time after each product? Which one should be applied first? Or would you rotate these two products since, let’s face it, most people aren’t going to add 40-60 minutes of wait time to their evening skincare routine?

    Really love the blog! 🙂

  47. Ad

    Hi Kerry,

    There is a new and improved formula for this product that was launched this year – Pure Vitamin C21.5 Advanced Serum. It would be great if you could do an update review on this product.

  48. Bobby H

    Hi there, im a boy and i just finish my breakout with bha, aha and tretinoin. My skin now is have only some acne left but much of acne scar and prone. I wonder whichs one will healing scar and prone better? The vitamin c ost serum or the benton snail bee essence/cream? I did researched and found 2 is the best but im not sure which one better ? Maybe when using ost i will have to skip my tretinoin for some weeks, not when with benton

  49. Sandy

    Hi Kerry, thanks very much for your review on C20! Meanwhile, the serum is being shipped to me and I can’t wait to try it.

    I am just wondering if I could apply Paula’s Choice 2% BHA Liquid Exfoliant or RESIST Weekly Resurfacing Treatment before applying C20…I am new to skincare chemicals and am pretty confused on how to layer them when it comes to “chemical reaction”.

    Much appreciate your advice…Thank you.

  50. Rini Asmara

    Hi dear, great blog! I’m a newbie in Vit C and want to ask you a quick question if you don’t mind 🙂

    So basically my routine is laneige – skin refiner, skinfood – black sugar perfect first serum, and then O.S.T Vitamin C. But I saw you write you use it directly on bare skin, so should I use my toner and perfect first serum after the vitamin C or just dispatch both of them and continue with the rest? Thank you so much!

  51. Really wish to try this serum but I’m not sure my super-sensitive skin will react to acid…

  52. Chris

    Is is it recommended to use it straight after toner? Or after essence? Is this suitable for a 20 year old (normal skin with blackheads problem) who just started the Korean Skincare routine?

  53. Vitamin C serum is the good productm. I have been using it for a little over a month, after using, my skin is much clearer, brighter, smooth. It’s wonderful, I think that I should buy for my mother and sister. Thanks for this

  54. Cayla

    Hi, is it better to dab it onto your skin or using cotton pad?