How to use chelating agents in cosmetic formulas

What chelating agents are used in cosmetic formulas?

Common chelating agents in cosmetic formulas are:

• disodium edta and tetrasodium edta:
  • usually used between 0.05 and 0.2%. 
  • synthetic.
  • not biodegradable.
• phytic acid/sodium phytate:
  • usually used between 0.05 and 0.2% - input varies on grade of material, check supplier recommendations
  • can enhance anti-oxidant efficacy by binding to enzymes which may otherwise cause oxidative reactions.
  • may be naturally derived – check your source to confirm.
  • biodegradable.
• citric acid:
  • usually added to a product formulation as a 50% w/v solution.
  • used as required for pH adjustment, it can also act as a chelating agent but it is not usually used in sufficient quantities to provide significant chelating benefits when use for pH adjustment.
  • naturally derived. 
  • biodegradable. 

When should chelating agents be used in cosmetic formulas?

Chelating agents may be used:

• in formulations where there may be free metal ions that could otherwise cause oxidation or discolouration of a product and thereby reduce its shelf life such as:
  • this includes magnesium or calcium that may be present in unsuitable process water.
  • process (manufacturing and lab) water should be demineralized (also referred to as deionized) so metal ions should not be present from your water source.
  • when pigments are used that contain ions.
  • actives containing magnesium, or ions from clays and even iron oxide from colourants and zinc and titanium dioxide.
  • acid-based preservatives - the use of a chelating agent can assist not only the preservative activity, but also support long term shelf life of the formula.
• in products such as shampoos or shower gels to reduce the formation of ‘scum’ when used by consumers in hard water areas. Surfactants that ‘need’ a chelating agent present to perform in hard water areas include traditionally saponified soaps and shaving creams as well as sulphate systems (whether naturally derived or not). It can be a good idea to add a small input of chelating agent in most foaming formulas because they can be used in hard water areas, so it helps ‘soften’ the water (slightly) during application anyway if a chelating agent is present. 
• where required by the use of certain actives and sunscreen agents – refer to supplier information to confirm if ingredients require chelating agents to ‘protect’ the efficacy of an ingredient or stability of a formulation.
• to boost preservative efficacy – the use of chelating agents can in many cases boost preservative efficacy, making them more effective. 
• to enhance antioxidant efficacy - the use of chelating agents to protect from free ion oxidative changes can help prevent some oxidative reactions from happening, enabling the antioxidant to protect the formula for longer, and more effectively.
  

Figure 1: how EDTA ‘chelates’ calcium ions in hard water sources

Should all cosmetic formulas contain a chelating agent?

If chelating agents are so useful, should they be used in every formula? The short answer is no. They will add charge to a formula, and this is not always a good thing for long term stability, nor is extra charge suitable for some ingredients. 

Only add chelating agents where they will improve the shelf life of a formula, and are not contra-indicated for other reasons; that is, only add them when you have a reason from our ‘should be used in formulas’ list where there is not also a reason from our ‘should not be used in’ list.

Happy formulating!