La Roche Posay's Serozinc is highly anticipated and highly raved (Source)
Escentual's site promotes Serozinc as "created with just three ingredients: La Roche-Posay’s ultra-soothing thermal spring water, healing zinc sulphate (0.10%) and astringent sodium chloride (0.75%). Together, these three ingredients target blemishes, marks and excess oiliness, ensuring your complexion feels fresh and comfortable at any time of day." So I guess we already know what the product is made of, and what the claims are. A lot of the rave reviews for Serozinc seem to have come from the fact that it is so simply formulated, which I suppose must be refreshing in a sea of products making complicated ingredient claims.
Serozinc is really getting a lot of hype despite the simple formulation (Source)
But before I start, I must clarify that I have never actually tried this product myself personally. Although ideally a more complete "review" (in the sense of a blog review) would have my own personal experience with the product woven in (as I do with my normal reviews), for the purposes of this post, we are looking at what the science says about the usefulness of Zinc Sulphate, which will in turn help consumers (like you and me!) decide whether it's really worth spending your hard-earned money on the product. So just take this as me doing your science homework for you, to help you make an educated decision before you buy the product! So, without further ado, let's take a look at the ingredients in the product!
As you might guess, the ingredients for Serozinc are no secret, since both La Roche Posay and Escentual make a point of advertising them. La Roche Posay's site has the ingredients, and thanks to Escentual, we also know the percentage of the ingredients too!:
Aqua (99.15%), Sodium Chloride (0.75%), Zinc Sulphate (0.10%)
I guess this means that effectively, you're paying for a product that is more than 99% water. And Sodium Chloride is just salt, like the table salt you add to your food. To be honest, I don't know if a product that is 99.15% water and then 0.75% salt is really worth paying for, although to be fair the price isn't that exorbitant - depending on where you are, prices vary from €6 to £8.50 if it's not. But I don't know if I'd pay £8 (or SGD$17 or so in my currency) for something that is more than 99% water and salt.
With over 99% of Serozinc made of water, your bottle of Serozinc has a greater percentage of water than a watermelon or lettuce (Source)
But price aside, and the idea of paying for a bottle of mostly-water aside, does Serozinc really work as advertised? Well for that, we'll have to analyze the ingredients. But there aren't that many ingredients to analyze here - water is well, water, and Sodium Chloride (aka table salt) doesn't do much for the skin in terms of effectiveness, but it is used variously in skincare as either a water-binding agent, or else a thickener. I'm guessing in this case that it probably functions more as a water binding agent, since the product is packaged in a spray form, so I'm assuming that thickening the product (which might make it more difficult to dispense via a spray bottle) was not the intent.
So I guess that leaves us really only one ingredient to analyze - zinc sulphate! What does zinc sulphate do in skincare, and does this mean the product would really work as advertised?
Zinc Sulphate: What effect does it have when applied to skin?
First, though, let's get some basics down about zinc sulphate. It's a compound with the molecular formula ZnSO₄. It's a pretty ordinary chemical compound - I remember back when I was in my teens, when I handled this compound in my science classes in school, we didn't have to wear any safety goggles or gloves. And if you want to know all about zinc sulphate, PubMed has a site listing all sorts of physical, chemical, and medical properties of zinc sulphate. Zinc sulphate is sold in tablet form as medicine, and these tablets are used to treat or prevent low levels of zinc in people. Some such trade name tablets include Orazinc, Zincate, and Solvazinc. Given these cute names, I guess it's no surprise why La Roche Posay named their zinc-for-the-skin product Serozinc!
Zinc Sulphate's molecular formula (Source)
Anyway, cutesy names aside, what does the science say about zinc sulphate, specifically with regards to zinc sulphate treating sensitive or blemish-prone skin, since Serozinc is, after all, meant as a toner for acne-prone skin? This is where the science seems to deviate from the marketing somewhat.
Zinc sulphate, seems to be a mixed bag, in terms of its effect topically on skin. There is some indication that it can aid wound healing, in part by reduce the risk of wound infection and enhancing re-epithelialization. It is also suggested that topical zinc may augment cutaneous immune responsiveness in humans. It was also proposed that a topical 10% zinc sulphate solution (coincidentally, the same percentage of zinc sulphate found in Serozinc) could help in the treatment of melasma, although subsequent studies questioned this by finding that the 10% zinc sulphate solution was not highly effective in reducing the severity of melasma, and also that it was not as effective in treating melasma as observed in previous studies. Other studies found that 10% zinc sulphate solution might help in treating plane warts, and that when combined with Clobetasol cream, was more effective in treating hand eczema than Clobetasol alone, and that topical formulations containing a zinc gel may be used to delay or prevent latex sensitivity.
Zinc sulphate in crystalline form (Source)
Specifically for acne skin, I could only find one study, and although the study found that topical zinc therapy alone is not of significant benefit in the treatment of acne vulgaris. So while the science regarding zinc and zinc sulphate might be interesting in other areas (e.g. in combination with other products to enhance treatment, or to help with wound healing and so on), it seems like as far as blemishes are concerned, the science seems to indicate that there isn't much basis for using zinc sulphate as an anti-acne treatment, especially when you consider that there are so many other products on the market containing ingredients with stronger science behind them (like products with salicylic acid, benzoyl peroxide, and so on). I'm personally not convinced, although of course I'm sure some people might find the product works for them.
If zinc sulphate doesn't add meaningfully to the product, then is Serozinc really different from La Roche Posay's other thermal water products?
[Edited to add: This section (up until the section on DIY Serozinc) has been added in light of feedback I've been receiving on this post. Thanks everyone who gave their feedback!]
So, basically the science regarding zinc sulphate is not convincing, especially if you're looking at the type of acne, blemished skin La Roche Posay is marketing Serozinc to. But how does Serozinc compare to La Roche Posay's other thermal water products? Is it meaningfully different in terms of effect on the skin, or is it pretty much similar to whatever other thermal water products the brand already has?
To get a comprehensive answer, we should probably evaluate this question from two perspectives:
1) Is the difference in formula meaningful?
In this case, since the main difference in formula is the addition of zinc sulphate and salt, and since neither salt nor zinc sulphate have a strong body of science behind their skincare benefits, I'm going to say that the change in formula doesn't change the product. So, we can conclude that it probably isn't meaningful.
2) Are the products formulated similarly?
To answer that, let's take a look at La Roche Posays Thermal Spring Water. The ingredients list, as per the La Roche Posay site, are:
AQUA / WATER
Yup. That's exactly what is listed on the site. So, if we compare formulas, Serozinc has water, salt, and zinc sulphate, the latter two ingredients which are questionable in terms of adding value to the formulation, while the Thermal Spring Water is just water. So yes, I'd say that the two products are formulated very similarly - you might even be able to call them dupes, pretty much, since they are 99.15% similar, with the remaining differences not being very significant. So if you've previously tried La Roche Posay's Thermal Spring Water and liked it, chances are, you will probably like Serozinc too. But on the other hand, if the Thermal Spring Water didn't seem to have any effect on your skin, it's unlikely that Serozinc will make a convert out of you.
Is DIY Serozinc possible, since Serozinc is so simple?
But anyway, I wanted to address the price issue with Serozinc. With a composition of 99.15% water, 0.75% table salt, and 0.10% zinc sulphate, even if it does work for me, the price just makes me a little uncomfortable. I mean, water is cheap, and so is table salt. And while zinc sulphate crystals probably need to be bought in bulk if you're a cosmetics manufacturer looking to manufacture skincare, it's probably pretty cheap too. A quick look at google throws up varying prices per ton of zinc sulphate, from $600-$900/ton to $430-450/ton, or 1000kg. Which means that since your 150ml bottle of Serozinc has probably less than a gram of zinc sulphate, so that $600, $900, or $400 for a ton of that stuff can go a long, long way - in essence, it can make over a million bottles of Serozinc!
Zinc sulphate tablets could aid you in DIYing your own Serozinc (Source)
Besides, since the product is so simple, this sounds like something I could make myself at home, for much cheaper! I'm guessing that you could reasonably DIY your own Serozinc with distilled water, salt, and zinc sulphate. I'm guessing that noone wants to buy a ton of zinc sulphate, so as an alternative, you could probably crack open or crush a zinc sulphate tablet to get zinc sulphate inside instead. And since both salt and zinc sulphate dissolve readily in water at room temperature, it's pretty easy to make too (other than the powdery mess you might get from crushing zinc sulphate tablets) - literally, just add water, salt, zinc sulphate, and stir. No heating, no special mixing or processes, no need to add ingredients in a certain order. It's probably pretty easy to DIY. I imagine the hardest part would be accurately measuring out less than a gram of salt or zinc sulphate, because this might require some specialized equipment or a pretty accurate scale.
Before anyone goes off to DIY their own Serozinc though - let me clarify that I've never tried DIYing this before myself, but this is my educated guess on how you could get a similar producdt at home. And if you do attempt to DIY your own Serozinc, please use distilled water (rather than tap water), and make sure all your jars, measuring instruments, and other implements are clean (at least wipe them down with isopropyl alcohol to disinfect them first).
TL;DR, just tell me if I should buy Serozinc or not!
So to sum up, what have we learned?
1) The formulation of Serozinc is 99.15% water, 0.75% table salt, and 0.10% zinc sulphate
2) The key ingredient, zinc sulphate, could have some potential skincare uses (including things like anti-inflammatory uses), but there is no proof that it helps acne or blemish skin get better
3) Because zinc sulphate doesn't seem to have that much use in terms of skincare, Serozinc isn't honestly very different from other La Roche Posay thermal water sprays.
4) The simple formulation of Serozinc means that it is possible to DIY your own version, because otherwise you would be paying for a product that is almost all water
Does this mean that you should go out and buy your bottle of Serozinc, or should you DIY your own, or should you not even bother, since the science for zinc sulphate helping acne skin is so scant? For me personally, with my acne skin, I'm kinda desperate enough to try everything that claims to cure acne at least once (hey, you never know, some hocus pocus magic could be in there that might help my skin!). But to be honest, even with my desperation, I'm not convinced enough to say that I would recommend you buy this. That said, I do generally like La Roche Posay's products, and I think the brand generally is a good one to pick as far as skincare goes, and I've given some of their other products a fairly positive review on my blog before. I guess I'm just not feelin' the utter love I've been seeing Serozinc get, because the science doesn't seem to show how it might work with helping acne. If it works for you, fine. But if it doesn't, and if you're wondering if you're the lone person not raving about the product, well, you know why!