What it is
Tetrasodium Etidronate is a phosphonate chelator that sequesters trace metal ions such as iron, calcium, and copper in a formula. By tying up these ions it helps prevent discoloration, preserve product stability, and support the performance of preservatives and other actives. It is used at very low levels as a stabilizing additive.
Safety & warnings
Chelating agents like tetrasodium etidronate are used at low concentrations and are generally well tolerated, with low potential for irritation or sensitization at cosmetic levels. It is not considered comedogenic.
Origin & sourcing
Synthetic. It is the tetrasodium salt of etidronic acid (a hydroxyethylidene diphosphonic acid).
Questions everyone asks
What is a chelating agent doing in sunscreen?
It binds trace metal ions that can degrade the formula, helping keep the product stable and supporting preservative performance.
Does tetrasodium etidronate affect the skin directly?
It is primarily a stabilizer working within the formula rather than an active skin ingredient, and is used at very low levels.