Introduction
In this blog we will be taking a look into what a chelating agent is, why and how we use them. We will also discuss when we use chelating agents and when not to use them, as well as providing the common chelating agents used in the cosmetic industry and their respective inputs.
What are chelating agents and what do they do?
Chelates are chemicals that control the reactivity of metal ions. (Nouryon, 2024). Metal ions can accelerate oxidative changes leading to bad aromas, discolouration and other signs of instability seen commonly in emulsions. Therefore by using a chelating agent you can extend the shelf life of your product by reducing the rate at which oxidation occurs. It is important to note however they are not preservatives and will not protect your formula against microbial contamination, only a broad spectrum preservative will do this.
When do we use chelating agents?
Chelating agents are used in almost every type of cosmetic product. They are not affected by heat so can be added during any phase when formulating cosmetics. Check the solubility of the chelating agent you plan to use in the safety data sheet so you know whether to solubilise it in water or oil. Normally these are water soluble substances, so you could add in your water phase, or in your cool down phase.
They are needed in formulas that contain oxidisable ingredients such magnesium, sodium, calcium, iron oxides, zinc oxide, titanium dioxide, or other ions present.
Where supplier information for active ingredients state it is needed.
Highly nutrient rich products to boost preservative efficacy.
Traditionally saponified products.
Where an acid based preservative is used.
Use of 0.1% chelating agent is quite standard in most emulsified and multi- phase personal care products. Control of trace metal ions with chelating agents can prevent discolouration, rancidity,
and other undesirable metal catalyzed reactions. Many products may also be protected from spoilage. Discolouration and rancidity of lotions may be prevented with 0.2 - 0.5% of a chelating agent.
It is recommended that all shampoo products include 0.1% chelating agents for control of deleterious spoilage. In addition, chelating agents may be used to soften the water with which
the liquid shampoo is diluted during manufacture.
In hard water areas, a water solution containing 0.5 - 1% of Dow chelating agent is an effective rinse for removing insoluble calcium and magnesium soaps. A similar rinse may also be used prior to cold waving or colouring. (The Dow Chemical Company, 2020).
When not to use chelating agents
Most products you see on the market will contain a chelating agent, however it is not always necessary to add one. Furthermore there are in fact instances where chelating agents should not be added.
Do not use in conjunction with electrolyte sensitive polymers such as carbomer, it can result in irreversible thinning and stability issues, reducing the efficacy of the product.
Do not use in conditioners or cationically charged products, chelating agents have a negative charge and will not be tolerated in products that contain cationcally charged substances such as the cationic surfactants used in hair conditioners.
Do not use in water in oil emulsions as this will lead to the system be destabilised.
Common chelating agents
The most common chelating agents used in the cosmetic industry are Disodium EDTA and tetrasodium EDTA they are synthetic, non biodegradable substances and used between 0.05 - 0.2%.
Phytic acid and sodium phytate conversely are normally biodegradable, naturally derived substances, used between 0.05 - 0.2%. Double check with your supplier to ensure the material you purchase merits the naturally derived status.
Citric acid is another naturally derived, biodegradable chelating agent. However due to the amount needed to provide the efficacy needed, and pH considerations it is not normally used as a chelating agent, its more common use is as a pH adjuster.
Conclusion
In this blog we have discussed what a chelating agent is and when and how to use them. We have discussed when not the use chelating agents, as well as provided some examples of common chelating agents used in the cosmetic industry and their recommended inputs in formulas.
References
Nouryon. (2024). Control metal ions and improve performance of your application. [Online]. [Date Accessed 21/08/2024]. Available at: https://www.nouryon.com/products/chelates/#
The Dow Chemical Company. (2020). Cosmetic, Toiletry and Other Personal Care Uses for Dow Chelating Agents. [Online]. [Date Accessed 21/08/2024]. Available at: https://www.dow.com/documents/113/113-01519-01-cosmetic-toiletry-and-personal-care-uses-for-dow-chelating-agents.pdf?iframe=true#:~:text=Control%20of%20trace%20metal%20ions,weight)%20of%20Dow%20chelating%20agent.