EDTA in Shampoos

Dear Valerie: I am currently using Tetrasodium EDTA in a shampoo at 0.2% and the pH is 4.0-4.5. Since EDTA is not very effective at this pH, should I increase the amount of EDTA to compensate for the reduced efficacy or remove it because at that level, the EDTA doesn’t do much, no matter how much I add? 

—Addition by Subtraction

Dear Addition:

In general, I’m not a fan of chelating agents, particularly EDTA. This may surprise you because I formulate hair color, where strong chelating agents in higher quantities are a must to protect the consumer from dangerous on-scalp reactions. However, I try not to use them where I don’t have to, due to their persistence in the environment. I’m even less a fan of using them when they’re not doing much!

My first inclination is remove it. But there is value to formulating with chelating agents. They can help reduce your preservative percentage or support a preservative that’s not particularly robust. The latter is particularly important in our day and age where we have artificial restrictions placed by brands and consumers on what preservatives can be used. If removing it isn’t an option, we must figure out a path forward as I would not increase the percentage to compensate for reduced efficacy. More of something that doesn’t work is just more of something that doesn’t work.

Your pH range is low, so firstly consider changing the type of EDTA you’re using to disodium EDTA. It’s better suited for lower pH ranges. Additionally, consider lowering the use level to 0.05% or 0.1%. The solubility of EDTA lower than pH 5 is not optimal. You may either find it difficult to incorporate or precipitate out over time if sticking with 0.2%. I recommend alternative chelating agents. If you are price sensitive, alternatives would not be a viable option, as they are not only more expensive, but have a lower binding affinity to metal ions over the EDTAs.

Valerie George
askvalerie@icloud.com

Valerie George is a cosmetic chemist, science communicator, educator, leader, and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care at her company, Simply Formulas, and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist or showcasing her favorite ingredients to small brands and home formulators at simply-ingredients.com