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I was really excited lớn finally get my hands on a bottle of O.S.T. Vitamin Cđôi mươi Serum. It’s been on my wish danh sách for a long time. I’m a big tín đồ 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 lớn phối tretinoin và 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 lớn use Vitamin C in the morning & 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 khổng lồ the tretinoin, và I just switched to lớn the micro-gel version (which I find to lớn 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, & I still think it every morning, as I’m applying this serum.

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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), và remove blackheads.


Ingredients: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/VPhường 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 danh sách looks okay at first glance, as this serum does contain a multitude of good skincare ingredients. There are also some things about this ingredient các mục that I find confusing, but I’ll get lớn 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 sầu formula, 15% is better, and 20% is pretty great. Topical Vitamin C has been scientifically proven as an effective sầu topical treatment for a variety of skin conditions, including acne, reduction in photodamage, fading of scars, & strengthening the skin’s barrier function. It also promotes collaren production, và 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 lớn light và 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 lớn be packaged in dark colored or opaque bottles – a clear bottle would render the sản phẩm ineffective sầu fairly quickly. It’s also important khổng lồ use up a Vitamin C hàng hóa within a a reasonably short span of time – 3 months is a good rule of thumb, but if your Vitamin C sản phẩm 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 lớn 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, & 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 lớn start:

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


Sodium Lactate – Sodium Lactate is a sodium salternative text derived from Lactic acid. It’s a highly effective antimicrobial agent . In fact, it’s often used as a preservative sầu in meat & 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 khổng lồ hold up 1,000 times its weight in water. This humectant also does a great job attracting và 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 lớn increase barrier function & ceramide levels, và 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 lớn be incompatible with Vitamin C, especially in the form of Ascorbic Acid as it appears in this serum. Niacinamide & 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 danh mục of active sầu ingredients in this formula, I’m guessing it’s not present enough to lớn 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 và can shed some light on why Niacinamide is included in this formula, I’d love your insight!


Ubiquinone – Better known as Coquận 10, Ubiquinone is an antioxidant that can help increase collagene production when present in large enough amounts. Ubiquinone is pretty low on the ingredient các mục in this particular formula, however, so once again, I find myself asking why it’s been included.

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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 Cđôi mươi Serum according lớn COSDNA, where the ingredient ranks a 3 out of 5 as a potential irritant. I’ve sầu mentioned here before that there are a large number of people who believe sầu that alcohol is harmful khổng lồ the skin in any amount and in any formula. There is also a line of thought that when included in a well-formulated sản phẩm, it is a beneficial ingredient because it increases the absorption of other skin-healthy ingredients. Based on the retìm kiếm available, which is best summed up in this FutureDerm article, I’m personally inclined khổng lồ fall inkhổng lồ the “alcohol can be good in a well-formulated product” side of the great debate.


PackagingThe 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 prsự kiện hàng hóa oxidation. It comes with a glass dropper cap, which is packaged separately khổng lồ prevent it from breaking during shipping. I would have preferred to lớn see this sản phẩm in an airless pump to prevent air exposure, but a dropper is fine – it would be my second choice.



SmellThis serum smells delightfully like fresh oranges.

ApplicationBefore I get into my application method, I’d lượt thích lớn point out that the O.S.T. Vitamin C20 Serum really is designed khổng lồ be used at night. The primary reason for this is its Ascorbic Acid nội dung, 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, và most days I get very little sun exposure – 22 minutes total for my drive sầu khổng lồ và from work. I skipped this serum on a couple of occasions when I knew I would be outside or in the oto 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 baông chồng when I was using the Perricone MD Vitamin C hàng hóa, I applied my C first thing after cleansing. That worked well for me, so I decided khổng lồ use this in a similar manner. I follow up with my facial oil, my sunscreen, an essence, và my moisturizer.



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 và don’t apply any additional skincare products afterward, that is 100% true. This serum glides on during application, but it does feel sticky to lớn 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 Ctrăng tròn 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 lớn alcohol as an ingredient in the right hàng hóa.

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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 lớn no fading. After the second week of using the O.S.T. Vitamin Ctrăng tròn 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, & 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 khổng lồ bình luận on whether this serum helps with either of those issues.