What it is
Disodium EDTA is one of the sodium salts of ethylenediaminetetraacetic acid, a synthetic aminopolycarboxylic acid. As a chelating agent it works by binding, or sequestering, metal ions such as iron and calcium that enter a formula through water and raw materials, locking them into stable, water-soluble complexes. By tying up these metal ions, it prevents them from catalyzing reactions that would otherwise degrade the product or reduce the effectiveness of preservatives. It is typically used at very low concentrations, on the order of 0.1 percent or less.
Safety & warnings
EDTA salts are used in cosmetics at very low levels and are generally well tolerated on skin. Because the function is purely formulation stability rather than a skin-active effect, exposure for the user is minimal. People with known sensitivities should still review full ingredient lists, but EDTA salts are not commonly associated with irritation at the trace concentrations used.
Origin & sourcing
Disodium EDTA is fully synthetic. The parent acid, EDTA, is manufactured industrially by reacting ethylenediamine (1,2-diaminoethane), formaldehyde, and sodium cyanide, a route that yields the tetrasodium salt and, after acidification with hydrochloric acid, the free acid forms; the disodium salt is one of the partially neutralized products. Worldwide EDTA output is on the order of 80,000 tonnes per year.
History
EDTA was first synthesized in 1935 by the chemist Ferdinand Munz, who prepared it from ethylenediamine and chloroacetic acid; the work was patented in 1938. The molecule is a hexadentate ligand, binding metal ions through its two amine and four carboxylate groups, which is the basis for its widespread use as a chelator in industry, medicine, and cosmetics.
Questions everyone asks
What does disodium EDTA do in a sunscreen?
It binds trace metal ions that sneak in through water and raw materials, helping the formula stay stable and helping preservatives work effectively. It is a behind-the-scenes stabilizer, not a sun-protective ingredient.
Is disodium EDTA natural?
No. It is a synthetic salt of EDTA, which is made industrially from ethylenediamine, formaldehyde, and sodium cyanide.
Why is it used at such low amounts?
Chelating agents are effective at very small concentrations, typically around 0.1 percent or less, because a little is enough to tie up the trace metals present in a formula.