The Beauty Of Chelating Agents – Cosmetic Formulating 101
Did you ever play with these as a child?
Those are stickle bricks or bristle blocks if you are from the USA.
They are also the closest thing in terms of free and easily relatable visual teaching aid that I can find to help communicate the power of the chelating agent.
If you are looking for a quick-fix definition and that’s all here it is. Chelating agents bind up trace metal ion contaminants in your water-containing cosmetic thus keeping the product microbe free for longer. They are not preservatives in their own right, they just help to kill microbes by starving them. They starve them by locking up or binding to their trace metal ion food supply.
In a cosmetic we use a small amount to boost preservative efficacy, especially in hard-to-preserve products.
But chelating agents are used in much higher volumes in other industries including water remediation, household cleaning, agrochemicals, textiles, chemical production, pharmaceutical manufacture, paint and coatings and soaping.
There are 141 Chelating agents registered in the European cosmetic ingredient database. Here are some of the most common ones:
EDTA – cheap, very effective and wide formula compatibility. Use at between 0.05-0.2% The down side is that this is made from petroleum derivatives and is therefore not a sustainable ‘green chemistry’ option. It also got a very bad wrap about ten years ago for its patchy biodegradability but since then the data gaps seem to have been filled and it now looks like as long as the soil is alkali EDTA biodegrades although some of the heavy metal complexes are more resistant to degradation and that is a worry. It is irritating to the eyes and skin in its neat form but then again most things are so that is less of a concern.
Sodium Phytate/ Phytic Acid – These are two of the new generation natural chelating agents. They are expensive though and are not as effective as EDTA BUT are natural and plant derived. Use between 0.1-0.3%
Citric Acid/ Sodium Citrate – This is a relatively poor chelating agent but it can help to boost preservative efficacy and bind some metal ions. Typically it is used at between 0.0-5-0.8% or to achieve a formula pH of between 4-5
Sodium Gluconate – This is a natural and gentle chelating agent which sounds lovely but I’m not sure you want your bug killers to be gentle. Anyway, it has a place and can help to boost preservation in natural formulations without sounding scary or overly ‘chemical. Use at 0.1-1% and best in acidic formulations.
NTA – This is what you get before you get EDTA so they are structurally similar. NTA is more commonly used as a chelator in industrial processes and cleaning products but rarely used in cosmetics.
EDDS (TRISODIUM ETHYLENEDIAMINE DISUCCINATE)– This is a structural isomer (same stuff but in a different order) of EDTA, an isomer that made it readily biodegradable. It is also made from sustainable resources so is a ‘green chemistry’ alternative to EDTA. EDDS came out of a company called Associated Octel whom I worked for when I was in the UK. We won a ‘Green Chemistry’ award for this and I spent many days talking to cleaning companies about how good it was vs EDTA so do check it out. Use between 0.05-0.2%
The next two have secondary chelating benefits that might be useful but shouldn’t necessarily be relied upon in difficult formulations.
Cyclodextrin – This works like a physical trap as cyclodextrins are structured a bit like Hoberman Spheres that trap metal ions inside them. Cyclodextrins are most often used in a formula to help protect and slow-release actives but this secondary chelating benefit is most welcome.
Activated Carbon (INCI: Charcoal) works like cyclodextrin too and can also help with chelation to a certain extent. Do see our post on Charcoal though to make sure you get the right stuff.
Here is a Hoberman Sphere, they make great toys!
Some natural extracts have chelating power too and there are a few listed on the European COSING database. Just be aware that while this is a great bonus, adding plant material to a formula makes it need a chelating agent more as plants come with trace metal ions. So in a way it is part of both the problem and the solution. As long as the benefits outweigh the risks I’d say that plant chelating is a great way to go.
I like to think of chelating agents as my tiny little soldiers that do an amazing job considering how little there is in the formula. I try to use chelating agents in all of my water containing formulations and recommend that you do too as a safe cosmetic is one that is microbially clean and protected.
Have fun experimenting and if you need my professional consulting help do drop me a line: amanda@realizebeauty.com
Amanda x
Realize Beauty 
I loved playing with these!
Thanks Amanda, this is a great article for someone like me, totally confused in preservation matter and beginning to understand chelating agents’ value in difficult to preserve formulations. Is glycerine a chelator? If so how efficient?
Thanks again, Ayse
Hi Ayse,
Glycerin is not a chelating agent. What it can do is reduce the amount of free water in a formula by sucking it up. If there is a very low level of free water the formula will be self-preserving. That said relying on glycerin in a cosmetic formula is not a good thing unless you have done your micro testing to prove the product is safe and clean.
Thanks Amanda. So, glycerine will be no help to me as my formula is 90% hydrosol. I read somewhere that glycerine could help in preservation. Thank you for making it clear how and why. It seems there is no safe escape from EDTA. As soon as I find a preservation system that makes sense to me and it is pH appropriate and so on, I will surely do the micro testing.
I’m having an hard time finding a supplier of Sodium Phytate/ Phytic Acid. Do you have any suggestions?
The manufacturer is Dr Straetmans. You could probably contact the manufacturer though their website and they will tell you of the correct distributor for your location. Not all materials are available in small lots though so check the minimum pack size before sampling to make sure you can access the material when you need to buy it as this is quite expensive, especially if you have to buy heaps of it.
Hello Amanda,
I’m thinking of using kojic acid as a chelating agent in my lamellar formulations which may contain several other actives eg Vit C, B, and E. What do you think? What pH for face to treat dry/hyperpigmentation/post acne scarring/ older skin?
Also what is the different pH that I should I keep the products for complexion, scalp and all over skin.
Does the pH of face change as one ages?
Thanks and happy 2019!
Hi there,
Thanks for the question. I hadn’t looked at using Kojic Acid as a chelating agent before so I’ve had to look that up and it looks like it does have capacity to chelate Iron III and Aluminium III which could be somewhat useful. I don’t know which vitamin C or B you are using or the pH of your product – you don’t seem to know that either? I think you need to go back and plan some of these things out and also do some further reading on vitamin C types to work out which pH is going to sit best with your C plus B combo. pH can be balanced for the skin or for the formula or you could formulate for both although that isn’t always possible. Look at what types of vitamin C are available as typically you have to formulate Ascorbic Acid at below pH 4 which isn’t pH balanced for skin (although it’s not too bad if you have a formula at 3.6-3.8). Anyway, there are still too many unknowns here that you have to figure out before I could offer a further opinion so it’s time to get reading 🙂
Dear Amanda,
is EDTA Calcium Disodium similar enough to EDTA to be as efficacious at chelation in a formula? And if its not too much trouble, do i add the chelator at the same time as the preservative system? (As in, during the cool-down phase?)..& i assume i pH it before & after adding it?
For some reason, i’ve had a bear of a time finding this information! So, i’d very much appreciate any help you might offer..thank you for all your generous assistance& kindness this year.
i hope you are having a lovely holiday season!
Muchlov, suki
Hi there,
Speaking of cosmetics only as that’s where my experience lies, it is the EDTA bit that does the chelating, the Calcium / DiSodium/ Tetrasodium is the salt which helps the ingredient solubilise better. Disodium EDTA is only around 1/5th as soluble as Tetrasodium EDTA in water but Disodium EDTA solution has a resting pH of 4-6 whereas Tetrasodium has a resting pH of 10-11. pH can, of course, be adjusted but adding more salts to the water may not be good for the formula, depending on what you are making. So the answer to the first part of the question is yes, they are similar but that their differing solubility at different pH may affect their suitability for your application. You can add a chelator at any time but often these are added at the beginning as EDTA solubility does increase with increased temperature so it is just an easy and reliable way to get it in and solubilised. You adjust the pH of your formula at the end as all water soluble ingredients can affect it. Just check out the Stability Constants for your target metals with the EDTA at different pH values to work out the optimal pH for your formula. As for the holidays, it’s been great, just what I needed to recharge my brain thanks!
Hi Amanda, I am using tetrasodium EDTA in my formula at the beginning of process and adjust the pH with citric acid at the end. My concern is, can high pH from tetrasodium EDTA degrade my active in the short time; because I only adjust the pH after I finish adding all of my actives. Should I adjust the pH right after dissolving my tetrasodium EDTA?
Thank you in advance, Hamizah.
There should be no issue in this but if you wish to adjust the pH of the formula before adding the active that you feel is pH sensitive, you could always do that too. If you really want to know if the order of pH change makes a difference you could always run stability studies of both options and assay the active to see which way (if any) protects it best.
Thank you Amanda for your clarification and suggestion. I will try your suggestion to run the stability studies.
Thank you for the article! how do you compare sodium gluconate and sodium phytate? which one is better chelator between the two as per your experience. Thank you!
Chelating agents can be compared using their Stability Constants with various metal ions. There is no ‘best’ chelator, it depends on your formula, what you are trying to chelate and what your product philosophy/ price point is.
The way to compare the efficacy of different chelating agents is to look at their stability constants. Stability constants are pH dependent so keep that in mind, it can also be quite hard to find data for everything that allows you to compare different things. In terms of what’s the best, there is no such thing. It’s an applied question so you have to think of what you are trying to chelate, the parameters of your formula, your price point, ingredient philosophy and what works well in your formulation. This takes a fair bit of formulating work so it’s back to the lab for you probably 🙂
Hi Amanda,
I thought I just posted a question about GluconoDeltaLactone. However, I have no proof of that, because WordPress told me I had to log in, AFTER I wrote my comment.
Would you let me know if you see this & there’s no other post with it?
Thank you, you are a Goddess!
Muchlove, suki
I can’t see it no. Just ask here.
Okay, this is my second (probably) lengthy post to you today. But here goes.
Is Sodium Gluconate related in any way to GluconoDeltaLactone?
From the manufacturer, of course, I learned that GDL is not only allegedly a chelating agent, but that it is also a ‘polyhydroxy acid’, which is supposed to be just as effective as an Alpha-hydroxy Acid, but generally much less irritating to the skin (than, specifically, glycolic acid).
Another quality, which I find to be its most intriguing, especially if true, is that GDL supposedly takes a formula’s pH to 3, over the course of an hour or two, & locks? it there.
First, I’d love to know if you have ever worked with this ingredient •as a chelating agent•; second, if you have worked with it as a PHA; & again, as a pH ‘buffering’ sort of thing. In my uneducated opinion, a person with normal skin, & an intact, healthy barrier could maybe acclimate to a pH of 3 if they took it slow & otherwise, moisturized & cleansed their skin with pH-balanced products. Am I off my rocker?
Lastly, I am about to do an experiment, hopefully this evening, with L-Ascorbic Acid & GDL, in distilled water, solely for the possibly absurd reason that I want to see if the pH climbs up to 3 (first, I have to see what GDL’s pH is, in solution, all by herself) & if it does, & then stays there, have I begun to make a more efficacious C solution/sera because more of the L-A A is closer to free acid? I hope that is not as silly as it sounds. I feel like its worth checking. (by the way, I don’t even know if L-Ascorbic Acid IS more efficient if its closer to its original pH. I suspect it might be, but then you’d still have to split the difference of how much damage your skin could afford to sustain at a lower pH!).
So, I think that is most of my queries about this fascinating ingredient.
Mostly, I really just want your take &/or any anecdotal or other data you might have on this stuff, which it just occurred to me might not even be allowed in your country!
I hope you have had a wonderful new year?/holiday? I am so confused as to what time of year it is in Australia right now!
Regardless, I wish you nothing but the absolute best for you & your family in this bugnuts-crazy time.
Sincerely & with all my respect & admiration,
Suki
I have worked with both sodium gluconate and Gluconodeltalactone. The first is the salt of gluconic acid and the second is an ester of gluconic acid. In solutions (most peoples formulations) you end up with both in equilibrium if you use the GDL. They do have many functions including the gluconic acid being a polyhydroxyacid. It’s present naturally in honey and gives honey a very mild exfoliating action on the skin. I haven’t done enough hands-on work to know how well it would replace AHA’s but I guess you could give it a go. I usually use it as a chelating agent, as part of a preservative system or as a pH adjuster and that’s it really. I will be looking more at this soonish though as it’s all part of the ‘where does it come from’ series of posts I’m thinking about with regards to active acids in skincare. I did a bit of research on it all before Christmas but have forgotten most of it again and lost my notes!