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L-AA is highly unstable, oxidizing rapidly from light, oxygen, and temperature. This is addressed by companies by packaging it in a dark or opaque bottle, and advising consumers to store it in the refrigerator or in a cool, dark space. Do not use Vitamin C serums that have oxidized. Oxidized Vitamin C is a pro-oxidant. At best, it's biologically inactive and does nothing for you, and at worst will damage/age your skin.

There are some ingredients that work well with L-AA. Vitamin E (aka Tocopherol or Tocopherol Acetate) is the John Watson to L-AA's Sherlock. They're great by themselves, but even better together (synergy). Adding Vitamin E to an L-AA serum, among other things, keeps it from oxidizing for longer. Ferulic Acid, another powerful antioxidant, can stabilize a Vitamin C+E solution and makes it eight times (!!!) more photoprotective.

Sodium Lactate is a humectant with some antimicrobial properties. It is listed in some places as being able to enhance Vitamin C's skin lightening properties, although there doesn't seem to be much research on it.

is a humectant with some antimicrobial properties. It is listed in some places as being able to enhance Vitamin C's skin lightening properties, although there doesn't seem to be much research on it. On the other hand, there are a couple of things that do not play well with L-AA. Sodium Benzoate is a common preservative, but when combined with L-AA, can form benzene, a carcinogenic compound. Niacinamide , aka Vitamin B3, is a great active, but when combined with L-AA, renders both of them useless - or in presence of UV, can be pro-oxidative. Some other controversial ingredients include green tea extract and copper peptides . Also, just because you cannot see damage does not mean damage is not being done.

is a common preservative, but when combined with L-AA, can form benzene, a carcinogenic compound. , aka Vitamin B3, is a great active, but when combined with L-AA, renders both of them useless - or in presence of UV, can be pro-oxidative. Some other controversial ingredients include and . Also, just because you cannot see damage does not mean damage is not being done. Despite being so fickle, L-AA is also the most commonly used Vitamin C vitamer because it is most effective, outperforming MAP and ATIP. And cheap.

Now, onto my deal with C20. It works. Pretty effectively. I've only purchased one bottle, so I can't say much for its collagen producing abilities, but it lightens up PIH beautifully. But picking at the ingredients, it has a lot of alcohol, niacinamide, orange essential oil, green tea extract, and just a whole lot of solvents that seem really unnecessary.





Alcohol isn't a bad thing on its own, but can be irritating, or in the least drying. Orange essential oil does not add any benefits, and is also a potential irritant. But really, the biggest concern for me was niacinamide. Why was it even in there? Yes, Korean skincare companies love putting niacinamide in everything, but this doesn't need it. L-AA already starts breaking down after the initial exposure to air. It doesn't matter if it's lower down on the ingredient list. Having it there at all just seems irresponsible and shows a lack of research. The green tea bit, there are some people who think that putting it together with L-AA is great, and some who think it's dangerous without a chelating agent. I think if there's controversy, it's best to just put it elsewhere until further studies show otherwises.





OK, so with that in mind, OST's C20 looks not that great, even with the lower price tag. It's not a bad product, and I don't think it will do irreversible damage to your skin, omg. I just don't think it's worth it. It's not that great of a formulation. But then 2015 rolled around, and they announced a new product! The C21.5! It's even better! Right?

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Ugh. I'm not asking for much, y'all. I want L-AA, between 15-20%, with a drop of Vitamin E, a smaller drop of Ferulic Acid, and some stuff that's not going to hurt my skin. No, I don't need the L-AA raised, as that can be potentially irritating, with no proof that it's any more effective. Yes, the sea buckthorn water (Hippophae Rhamnoides) is neat, but I'd rather they just used Vitamin E, sea buckthorn oil, and just emulsified it. Nothing here justifies the increase in price. There's no reason for them to keep the same ingredients in the C20. Just ugh, man.



So will I be purchasing the C21.5 to try?





I'll be DIYing, thanks. If you're game, join me in a few weeks, or just



If DIY isn't for you though, there are still affordable, effective options out there. SkinActives has one for



What other Vitamin C serums do you recommend? Ugh. I'm not asking for much, y'all. I want L-AA, between 15-20%, with a drop of Vitamin E, a smaller drop of Ferulic Acid, and some stuff that's not going to hurt my skin. No, I don't need the L-AA raised, as that can be potentially irritating, with no proof that it's any more effective. Yes, the sea buckthorn water (Hippophae Rhamnoides) is neat, but I'd rather they just used Vitamin E, sea buckthorn oil, and just emulsified it. Nothing here justifies the increase in price. There's no reason for them to keep the same ingredients in the C20. Just, man.So will I be purchasing the C21.5 to try?I'll be DIYing, thanks. If you're game, join me in a few weeks, or just google it . There are so many recipes out there, even some that knock off the fancy $150 Skinceuticals one . There's even a subreddit full of DIY recipes.If DIY isn't for you though, there are still affordable, effective options out there. SkinActives has one for even cheaper than the original C20, and NuFountain even has Prime shipping What other Vitamin C serums do you recommend?

Hi everyone! I ran out of my OST C20 a couple of weeks ago, and have been debating DIY vs rebuying, or at least buying a different Vitamin C serum to tide me over. Now, I'm not a chemist - taking a couple of chemistry classes in college does not a chemist make - but I did do some research into Vitamin C, and what I've found is kind of upsetting.The most notable ingredient in here is obviously, aka Vitamin C, although I will refer to it as(L-Ascorbic Acid) for the rest of this post. L-AA is kind of a superstar active that I think pretty much everyone should be using. It's a powerful antioxidant whose functions include stimulating collagen production, fading hyperpigmentation, scavenging free radicals, and boosting sun protection. Because L-AA requires a low pH to be effective, it also has a mild exfoliating effect (it's also an AHA). Seriously, it's just amazing.It's also one of the most well researched actives in skincare. Not hard to believe, as anything that can do all that and more will make money. And make does . It makes sense why OST skyrocketed into being one of the bestselling products in the Korean beauty market. A $20 (~$15-$25ish) product compared to $50, or even $150? Heck yeah! ...Right?To summarize, there are a few things about Vitamin C that are pretty important:Yes, less ingredients... I like that...Wait, what? This isn't the new C20? This is a different product? They're still selling the other one as well? This one? They dropped the Vitamin E?