When reviewing some cosmetic ingredients, especially polymers or some actives, you may have seen instructions such as: ‘not stable with electrolytes’; or ‘electrolyte sensitive’.
What exactly does this mean, and what are electrolytes?
More importantly, how can you avoid them in formulas where certain cosmetic ingredients are not compatible, and what should you be checking for to ensure you are making the right selections and cosmetic formulation combinations?
Electrolytes in cosmetic formulas
Chemically speaking, electrolytes are any mineral that will carry a positive or negative charge when dissolved in water.
While this positive or negative charge may be advantageous to ensure the mineral has the desired effect in the formula or when applied to the skin, it may be a disadvantage where it impacts the shelf life or compatibility of other cosmetic ingredients in a formula.
The following materials are considered electrolytes, and can typically be found in various types of cosmetic formulas:
- Sodium chloride and other salts – sodium chloride is commonly added to salt-responsive surfactant formulas to help increase viscosity.
- Actives with sodium, magnesium, zinc or iron in their INCI name – this includes sodium PCA, zinc oxide and iron oxides (in colour products).
- Sodium EDTA and phytic acid – these are chelating agents and are commonly used in a range of formulas where chelation is required.
- Acids – this is particularly relevant when using AHAs and BHAs.
- Excess pH adjusters (acid and alkali) – extreme pH formulas should also be considered as electrolyte-rich.
When are electrolytes a problem?
Polymers are the most commonly affected class of cosmetic ingredients when it comes to electrolyte exposure.
There are several types of polymers that will not tolerate electrolytes at all, such as carbomers, alkyl acrylates and cross polymers.
When using polymers, you should only adjust to the required pH to activate the polymer, but then don’t adjust pH again after that point, otherwise they will be irreversibly thinned.
Some actives specifically require chelating agents; in these cases you will need to choose polymers carefully. Look for polymers listed as ‘electrolyte resistant’ or ‘electrolyte stable’, but be wary of the following:
- Suppliers may say ‘electrolyte tolerant’ – these polymers may tolerate small amounts of EDTA and a broader than normal pH range (e.g. 5-8).
- Look for ‘electrolyte resistant’ – if electrolytes will be present or using other polymers turns your formula to water, you need to look specifically for ‘electrolyte resistant’ polymers.
- If you can’t find ‘electrolyte resistant’ in the supplier’s description, assume the polymer can’t tolerate electrolytes and choose a different material.
If you have an active or other functional ingredient that is affected by electrolytes, you will need to avoid that ingredient or remove the electrolytes from your formula.
How to avoid electrolytes
If you are not sure if your formula might be carrying electrolytes, check the ingredients used:
- Refer to the list above for very strong and active electrolytes that can inhibit electrolyte-sensitive ingredients.
- Check if your formula has anionic or cationic materials present. These can be the emulsifiers or surfactants in that formula and will create charge. When used in significant quantities, they will impart that charge to the formula and this can cause an issue for electrolyte-sensitive ingredients.
- If your formula contains charged ingredients or electrolytes, you may need to select neutral polymers or natural gums which are typically more electrolyte resistant or may be able to withstand certain extreme environments. Remember to check technical data sheets carefully especially when you need certain electrolytes present. You can also ask your supplier for their electrolyte-resistant polymer or functional ingredient options.
If the sample from your cosmetic formula has an unexpectedly low viscosity or colour change, there is likely to be an incompatibility with the ingredients present and often, an electrolyte.
Check the formula carefully and you will often be able to identify the problem and find the solution.