Key takeaways
- Chelators bind iron and copper that catalyse oxidation and discoloration
- Disodium EDTA at 0.05-0.2 percent works across a wide pH range
- Phytic acid loses strength above pH 6; it suits low-pH formulas
- Sodium phytate is milder and usually needs a higher dose than EDTA
- A chelator boosts preservatives but never replaces a challenge test
Chelating agents bind trace metals that catalyse oxidation, destabilise emulsions and feed microbial growth. They are rarely the ingredient a customer notices, yet removing one often turns a stable formula into a discoloured one within a few months. The choice between EDTA and phytate is mostly about pH, marketing position and dose.
1. What chelation does in a formula
A chelator wraps around a metal ion and holds it in a ring structure, so the ion can no longer participate in reactions. Iron and copper are the main targets: both catalyse oxidation of oils and fragrances at parts per million levels. Chelation also weakens the outer membrane of many bacteria, which makes preservatives work better.
2. The metals that cause trouble
Iron arrives through water, pigment and equipment contact. Copper comes from pumps and pipework. Calcium and magnesium arrive with water and with some thickeners, and they interfere with anionic emulsifiers and with foam. A formula’s metal load is usually highest in the first batch after a shutdown.
3. EDTA and its salts
Disodium EDTA is the standard choice, effective across a wide pH range and cheap. Typical use is 0.05 to 0.2 percent. Above 0.2 percent there is little added benefit in most emulsions, and the extra dose can affect viscosity in carbomer systems. Tetrasodium EDTA suits alkaline formulas where disodium is less soluble.
4. Phytic acid and the pH question
Phytic acid is a plant-derived chelator with six phosphate groups and strong affinity for iron. Its performance falls sharply above pH 6, where it is fully deprotonated and much less effective at holding metals. It also contributes acidity, so it belongs in low-pH formulas such as exfoliating essences rather than neutral creams.
5. Sodium phytate as a mild alternative
Sodium phytate is the neutralised form, easier to handle and less acidic. It is usually dosed at 0.05 to 0.1 percent. It carries a plant-derived story, which is why it appears in clean-positioning formulas. In most cases it chelates less strongly than EDTA at the same weight, so the dose often needs to rise to match performance.
6. Dose ranges worth testing
Run a small screen at 0, 0.05, 0.1 and 0.2 percent and measure colour after accelerated storage. The useful dose is the lowest one that holds colour and odour, not the highest one the brief allows. On formulas with high pigment or high oil load, 0.1 percent is a common starting point.
7. Chelators and preservatives together
Chelators are often described as preservative boosters, and the description is fair but limited. They improve the activity of many preservative systems against gram-negative bacteria. They do not replace a challenge test. A formula with a chelator and an underdosed preservative still fails, sometimes faster because growth is delayed rather than prevented.
8. Colour and odour stability
Discoloration in a cream is often a metal-catalysed oxidation of a botanical extract or a fragrance component. Adding a chelator late in development can rescue such a formula, but it works better as a design decision. If a formula browns in accelerated storage at 40 degrees, chelation is one of the first three variables to check.
9. What to test
Test colour and odour at 40 degrees over twelve weeks with and without the chelator, and check viscosity in thickener systems. For phytate, confirm performance at the formula’s real pH rather than the pH on the brief. Also confirm the chelator does not precipitate with cationic ingredients, which it can.
10. Where it fits
Chelation matters most in essences and acid serums where pH is low. Compare notes in the encyclopedia and product formats.
Reference: Formulation development notes, 2025
