What is Etidronic Acid and Why is it Used in Personal Care?
Etidronic acid, also known as HEDP, is a type of phosphonate compound that acts as a chelating agent. In plain English, this means it’s very good at grabbing hold of metal ions—like calcium, iron, and copper—and stopping them from interfering with the rest of the ingredients in a product. This is useful in personal care because even tiny traces of metals can spoil the appearance, texture, or shelf life of things like creams, shampoos, and soaps. Etidronic acid helps keep these products stable and looking fresh for longer.
Why is it Used in Hair Care?
If you’ve ever struggled with dull hair or shampoo that doesn’t lather well, especially in a hard water area, you’ll appreciate why etidronic acid is added to hair care products. Hard water contains minerals that can build up on your hair and scalp, making products less effective. Etidronic acid binds to these minerals, stopping them from interfering with the cleansing and conditioning process. This means your shampoo works better, your conditioner leaves your hair softer, and you’re less likely to end up with that heavy, lifeless feeling.
It is also the case that it improves colour development in hair dyes.
The explanation seems to be something to do with metal ions. That metal ions can have a big impact on colour is well known. Think about the way copper sulfate gives a blue colour in the solutions you might remember from chemistry lessons at school, and the way copper things like the Statue of Liberty green. But I have to say I am not sure I understand exactly how it works in hair dyes. I don’t think anyone else does either.
Why is it Used in Eyelash Products?
Eyelash products, such as tints and serums, often include etidronic acid for similar reasons as in hair care. It helps keep the formula stable by binding stray metal ions that might otherwise cause the product to break down or change colour over time. For something that goes near your eyes, you want a product that stays safe and reliable from the first use to the last. But the main motive is that it helps develop a strong colour.
What is the Regulatory Position of Etidronic Acid?
Etidronic acid is allowed in cosmetics in the UK and EU, but there are restrictions on how much can be used. For example, in hair care products, the maximum permitted concentration is 1.5%, and in soaps it’s 0.2%. These limits are set to make sure the ingredient is safe for regular use, and are plenty to get the full effect.
Regulatory bodies have reviewed its safety and approved it for use at these levels. There are environmental issues with chelating agents as a class. These should be, and are being, addressed. But the contribution of personal care products is trivial compared to other uses. When biodegradable alternatives are available, no doubt the personal care industry will switch to them one way or another.