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Sodium Metabisulfite an antioxidant?
I’ve seen sodium metabisulfite in at least one skincare formulation so far and I’m curious if it fulfils a role in protecting the formulation against oxidation. Does it offer anything that alpha-tocopherol does not?
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19 Replies
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Correct, it is an antioxidant. It’s great for removing air from the formulation, something tocopherol does not. Ascorbic acid does it too though not as efficient. Like ascorbic acid, metabisulfite is water soluble and also a good partner for tocopherol (both regenerate ‘spent’ tocopherol). It is a quite strong antioxidant and hence, does react with more ingredients (such as natural pigments) than other antioxidants but does not protect as long because it gets used up fairly quickly by the ever present oxygen if not used in an airless dispenser. It’s also a possible allergen (if memory serves me right, ~1% of the population is allergic to sulfites in food, tendency decreasing due to less abundant use, though no precise numbers are known).
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What Pharma said holds true. (Thanks, Pharma) I’ve long thought sodium metabilsulfite an underrated ingredient in personal care, especially given its water-solubility and low cost. I’ve used it when formulating with highly oxidation-sensitive materials such as resveratrol, anthocyanins.
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Hi guys, while two experts are here, may I ask you to advise some source (cosmetic formulation book, article etc) where I can find more on antioxidants? I find information here and there but I can’t find a comprehensive guidance on which one to use with which ingredients. I see BHT used for retinol, ferulic acid for LAA and sodium metabisulfite for hydroquinone but not being a chemist I don’t know whether there’s a logic behind it or it’s trial and error.
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I haven’t found a book on antioxidants which would even remotely satisfy me ;( .However, there is logic to it (apart from a lot of trial and error as well): redox potential which can be listed in an electropotential series (see tables & figures in THIS topic-unrelated publication). What this means is, that in order to protect substance A from oxidation, substance B has to be a stronger antioxidant than A. In case of BHT/retinol: BHT is a highly sterically hindered phenol which results in a more stable radical whereas retinol can be regenerated but also tends to react further and thereby would degrade irreversibly. Although both are phenols with similar redox potentials, BHT is the fall guy due to stability. But this is just an exception to the rule of redox potential.Also, it sometimes pays off to choose couples either for one or for two electron reduction/oxidation but this may be more for lab settings. After all, mother nature goes with redox potential and spatial separation (lipophilic and hydrophilic antioxidants and different organelles for different redox steps). The latter is not readily applicable in cosmetics and doesn’t bring any benefits because a cosmetic product isn’t alive and constantly regenerating.
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I have renewed interest in sodium metabisulfite in part out of desperation, and also after reading about it on CC and after seeing it in use hereby Givaudan, perhaps because of the green tea content?
https://www.ulprospector.com/en/na/PersonalCare/Detail/829/367356/Redensyl
Additionally, as much as I don’t love this woman, I would think she went to a reputable formulator develop her skincare line. I’m semi-surprised they felt the need to include the ingredient here in her vitamin C serum given they/she very obviously got the idea from Skinceuticals, which does not use the ingredient.
ulprospector.com
Redensyl® by Givaudan Active Beauty - Personal Care & Cosmetics
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Are you fully understanding the aspects of how antioxidants work in emulsions?
Rule # 1 … Day one of cosmetic training. Rule number 1 is….. antioxidants only work in the phase they are soluble in! Hence all the E and ROE in the world….will not touch something that is oxidizing in the water phase (yes this still holds true, when the phases are combined…..they only look combined to your eye…and why they are still referred to as inner and outer phase….even once combined).
So, the ingredients you mentioned….will work wonders…. for ingredients that are water soluble, and thinking about oxidizing.
Take-away….is this does NOT replace E or ROE….but works along side it….in the opposite phase.
Good luck.
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BTW….this ingredient gets used more often than you can begin to imagine!!!!!!!!!!!!!!!!!!!
Just most folks will list it on the inci….as…. wait for it…. Fragrance. ????
What do you think is sold to beginners…to keep their vanilla (vanillin) scented products from browning????? (And it always has the inci: fragrance.) One of those little loopholes…. Shhhhhh.
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So, in your example….where they are fragrance free….they had no way to hide it. 🙂
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I have heard (not ever used) the benchmark brand will begin to discolor once opened. I would suspect the imposter….will discolor at a slower rate. ????
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Thank you. Just to clarify:
For this product in particular I am working on, it is not an emulsion. It’s just a serum/toner.
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If it is water based…you use water soluble anti-ox’s
If it is oil based…. you use oil soluble anti-ox’s.
????
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Yes. Sorry if I’m not being clear, but I already knew that.
I think the question I had (originally) were what could I use to (help) stabilize antioxidants like EGCG other than going airless.
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Usually keeping inclusion rate at .01% does a pretty good job. 🙂 Leaving it out all together, I found to be the best solution. Drink tea while formulating. But if something were to work….the aforementioned…would be a good choice.
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I think you mean 0.1%, no?
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Nope…. .01% works far better than .1%. ????
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This is very interesting. Where did you hear/learn of this? (Curious to see if others on Chemists Corner have had similar results…)
For what it’s worth, instructions from one of the sodium ascorbyl phosphate manufacturers recommended inclusion at 0.1%, but perhaps that’s because many formulators use SAP at a fairly high percentage (often 5%) and hence more sodium metabisulfite would be required in a preparation like that? I’m not sure.
Regardless, I did see elsewhere online that sodium metabisulfite, like all antioxidants, can itself become pro-oxidant, so perhaps less is better in this case.
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Ahhhh…. We badly miscommunicated…I was referring to the inclusion rate of the green tea. All problems with it….go away with the proper inclusion rate of .01%, or even .001%. ????
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Now, I get it 🙂
But back to sodium metabisulfite….usage is typically 0.1%? Or not sure?
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That sound like a good starting place, it can be used from .01 to .3%. When I was working with it….I was using the higher end of the range…as I was trying to keep Vanillin from oxidizing and was using big piles of vanillin….like several percent! (I never succeeded….and this was in the combination with the most brilliant mind to ever grace this site!) Good news is… nothing worse than a big pile of Vanillin!
To evaluate your success….put finished product in a clear container….and in a sunny window….won’t be long…before you can evaluate success or failure.
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