Cosrx BHA Blackhead Power Liquid has been a huge part of my routine since mid November of 2017. Since I am very acne-prone I use it daily, and sometimes twice daily. I had a period of time in January 2018 where my acne was flaring up and I couldn't seem to get it under control so I switched to using The Ordinary Salicylic Acid 2% Solution and Oxy Deep Pore Medicated Acne Pads with 2% salicylic acid. Things got worse: my acne persisted and my skin became even more irritated. I switched back to Cosrx BHA Blackhead Power Liquid and my skin gradually began to recover from irritation. However, I am not saying that it was the two salicylic acid containing products that caused the acne or the irritation.

I have been making all kinds of skincare mistakes despite supposedly knowing better. I ended up somewhat over-exfoliated recently due to a combination of things, as well as finding out the hard way that one of my trigger ingredients is lanolin. Long story short: Eucerin Aquaphor causes my skin to break out in painful little pustules that aren't fixed by applying acne solutions. It took me a while to realize that my acids were only worsening the problem by weakening the already irritated skin barrier that I would then apply more Aquaphor to fix. Once I ditched the Aquaphor the pustules healed and I was no longer stuck in the cycle of trying to treat a reaction as acne.

I have played around with The Ordinary Salicylic Acid 2% Solution and the Oxy Deep Pore Medicated Acne Pads since ditching Eucerin Aquaphor, and they have not caused anywhere near the level of irritation I previously experienced. However, I still don't like using them as much. Why? Well, the Oxy Pads are rough, stinky and very drying, and The Ordinary Salicylic Acid 2% Solution can be drying as well. These problems are not entirely the fault of the 2% salicylic acid that they contain. It's likely that my skin prefers Cosrx BHA Blackhead Power Liquid not because of the 4% betaine salicylate it contains, but because of the overall formulation. Let's look at the ingredients for all three products.

BHAs all day

Cosrx BHA Blackhead Power Liquid (list taken from Ulta): Salix Alba (Willow) Bark Water, Butylene Glycol, Betaine Salicylate, Niacinamide, 1,2-Hexanediol, Arginine, Panthenol, Sodium Hyaluronate, Xanthan Gum, Ethyl Hexanediol.

*sings* One of these things is not like the other..

The Ordinary Salicylic Acid 2% Solution (from their website): Aqua (Water), Hamamelis Virginiana Leaf Water, Cocamidopropyl Dimethylamine, Salicylic Acid, Dimethyl Isosorbide, Trisodium Ethylenediamine Disuccinate, Citric Acid, Polysorbate 20, Hydroxyethylcellulose, Ethoxydiglycol, Potassium Sorbate, Sodium Benzoate, 1,2-hexanediol, Caprylyl Glycol.

See? Look at how rough that pad is!

Oxy Deep Pore Medicated Acne Pads (transcribed from container): Salicylic Acid 2%, Non-Medicinal Ingredients: Fragrance, Isoceteth-20, PEG-8/SMDI Copolymer, Purified Water, SD Alcohol 40D, Triethanlomine, Trisodium EDTA.


Looking at all three lists of ingredients doesn't really clarify things. For one thing, I don't think the ingredients on the container of Oxy Pads is in order of most to least, rather it looks like alphabetical ordering. Why else would Fragrance be listed before Purified Water? Nonetheless, alcohol is apparent in the smell and feel of the liquid which is probably why these pads are very drying. I also really dislike the rough texture of the pad. It's very scratchy feeling ◉_◉

The difference between the ingredient lists for Cosrx BHA Blackhead Power Liquid and The Ordinary Salicylic Acid 2% Solution doesn't tell me much about why my skin prefers one over the other. To really find out, I will probably have to quit using the Cosrx for around 3 months and use The Ordinary instead. I'm not super keen to do that right at the moment since I like how the Blackhead Power Liquid feels under my other layers of skincare. Instead, we'll look at what are the differences between salicylic acid and betaine salicylate, and why they are used in concentrations of less than 2% and 4% respectively.

Let's begin with salicylic acid since it's what I am more familiar with; having used it on and off since I was eleven years old. Salicylic acid is a beta hydroxy acid, or BHA, originally derived from willow bark. Currently, it can be derived from a number of other sources including wintergreen, peanuts, licorice root, calendula (marigold), plantain, and wheat. The proper chemical name is 2-Hydroxybenzoic acid and Health Canada has it listed on its Cosmetic Ingredient Hotlist in the List of Ingredients that are Restricted for Use in Cosmetic Products. Surprisingly there isn't a tonne of other information to be found on Health Canada's site specifically pertaining to salicylic acid. All I've got is: "For topical use only. Permitted at concentrations equal to or less than 2%." Okie dokie then.

In Canada and the U.S. its concentration is capped at 2% for leave-on topical preparations (with the exception of certain foot condition treatments) but in Korea it is limited to 0.5%. At that low of a concentration it is unlikely to be effective for people suffering from severe acne. I believe this is why Cosrx has chosen to use betaine salicylate since the maximum allowable concentration is much higher. I have yet to find what the official maximum allowable concentration is, but I have not seen any product using higher than 4% betaine salicylate. One source states that 4% betaine salicylate acts the same as 2% salicylic acid, but I haven't seen any hard data to support that statement. Betaine salicylate has virtually no information listed about it on Health Canada. It is not mentioned whatsoever in Canada's Cosmetic Ingredient Hotlist. Nor, is it listed in the Cosmetics Ingredient Review, the Cosmetics Info, the Cosmetics and Toiletries, nor the Prospector databases. To me this indicates that either it is sufficiently uncommon and therefore merits no mention, OR it is completely safe with no side effects at all. My guess is the former.

Well that didn't clarify much. Image source 1 and source 2

Betaine salicylate is an ester of salicylic acid, meaning that a salicylic acid molecule has undergone a process called esterification in order to attach a betaine molecule. I last took chemistry in high school so I honestly can't completely understand the process. What I've read is essentially that the salicylic acid is placed in a waterless alcoholic solution and has a betaine molecule attached to it. Chemistry is magic, guys.

So what about the the betaine part of betaine salicylate? What is it and why is it there? Betaine is an amino acid derivative originally discovered in sugar beets. There are many types of betaine, but in skincare the type you find is actually trimethylglycine or TMG. You probably have seen it in many of your own skincare products because it acts as a skin conditioner and moisturizer, and is generally considered as a soothing superstar. If you check the ingredients in your hair care products you'll almost definitely find betaine because of the characteristic silky feeling that it imparts. This article from 2010 quickly summarizes some of the studies about betaine's safety, uses, and benefits. Most notable in my opinion is that "betaine has a good anti-inflammatory action on superficial inflammatory lesions". Less red and swollen acne spots gets a win in my book!

Alright, so they put the salicylic acid and betaine together to form betaine salicylate. Now what? From Patent US3002886A: "Betaine salicylate is slightly soluble in water (0.74 gram percent at 25 C.), and the pH of the saturated aqueous solution is pH 2.7. The compound is soluble in methanol, ethanol and isopropanol and insoluble in anhydrous ether and petroleum benzine. Betaine salicylate is not hygroscopic and is stable to heat and light."

When I first read that I had trouble understanding what 0.74 gram percent actually meant in practical terms. Particularly since 'gram percent' is non-standard notation these days. After some reading and using this great guide, I determined that the author means w/w% which is definitely something I have seen on my products without ever knowing what it meant. In fact, if you scroll up to the image of the container of Oxy pads and look closely at the right-most image you will see it too! Right there, on the line for medicinal ingredients it says "Salicylic Acid 2.0% w/w". Huh, why did I always ignore the w/w? Welp, the more you know I guess.

Okay, but if you can only dissolve 0.74g of betaine salicylate into 100g of water (or mL since they are equivalent for pure water in standard atmospheric condition) to reach a saturated solution, how can my skincare product have a 4% (ie. 4g betaine salicylate to 100g water) concentration? I am going to skip answering that question because I can't do it without going even further off-topic. Let's just say it has to do with the other solvents like butylene glycol, dimethyl isosorbide, and alcohol present in the formulations of the products we're talking about. I can't go down every rabbit hole, despite my natural inclination to so I'm noping right out of this one.

I pretty much only use these guys now since the OXY pads are ouch!

In conclusion, I don't think I answered my questions at all. I feel like I know less now that I did when I first began. There are so many factors in the formulation of a skincare product, and even more when that skincare product contains active ingredients. I hope that you learned something from reading this overly long post and if I have made mistakes, pleasepleaseplease correct me by commenting below!

To learn more about the power of acids in skincare, please check out Lab Muffin and her fantastic guides. There are lots and lots of blog posts about beta hydroxy acids and more over at Point of Interest, Vanity Rex, Graceful Face, Simple Skincare Science, The Wanderlust Project, Beauty Brains, Elizabeth Renee, and Escaping Mars.

Further Reading (but if you don't want to, that's okay)

Skincare Guide to Beta Hydroxy Acids

International Journal of Cosmetic Sciences

Comparison study of glycolic acid versus salicylic acid for sun damage

Salicylic acid as a skin whitening ingredient

Salicylic acid in wash-off products

Plant based sources of salicylic acid and other acne treatments

Delivery methods for salicylic acid in skincare

Sodium salicylate for anti-aging


Sources relating to the creation and purchase of betaine salicylate and salicylic acid

Patent for creating tablets of betaine salicylate

Cosmetics and Toiletries profile of salicylic acid

Prospector profile of salicylic acid

Prospector data relating to purchase of salicylic acid

Prospector data relating to purchase of betaine salicylate

in-cosmetics Korea data relating to purchase of betaine salicylate