What it is
Etidronic acid is a phosphonic acid that sequesters metal ions such as iron, calcium, and copper that can enter a formula from water or raw materials. By tying up these ions it helps prevent discoloration, off-odors, and breakdown of sensitive ingredients, and it can support the performance of preservatives and antioxidants. It is typically used at very low levels and is often present as its salt form in finished products.
Safety & warnings
Etidronic acid is used at low concentrations and is generally well tolerated on skin. It is not regarded as a common allergen or a comedogenic ingredient. As an acid, it is typically buffered or neutralized within the formula so the finished product is at a skin-appropriate pH.
Origin & sourcing
Etidronic acid is a synthetic phosphonate compound made through industrial chemical synthesis.
Questions everyone asks
Why is etidronic acid in my sunscreen?
It binds trace metal ions that could otherwise cause discoloration, odor, or ingredient breakdown, helping keep the formula stable over its shelf life.
Does etidronic acid exfoliate like an acid?
No. Despite the name, it is a chelating agent used at low levels for stability, not an exfoliating acid.