What it is
Sodium citrate refers to the sodium salts of citric acid, which exist as monosodium, disodium, and trisodium forms, with trisodium citrate the most common. In cosmetics it is used to adjust and buffer a product's pH so the formula stays within a target acidity range, and as a chelating (sequestering) agent that binds metal ions, often introduced through water, to prevent metal-catalyzed degradation. The same chelating chemistry, in which citrate binds calcium and other metal ions, underlies its established use as a food additive and laboratory anticoagulant.
Safety & warnings
Sodium citrate is a mild, well-tolerated pH-adjusting and chelating ingredient used at small amounts in cosmetics and is recognized as safe in food applications by the U.S. FDA. Because it is used to fine-tune acidity, the relevant consideration in skincare is the finished product's overall pH rather than the ingredient itself, and it is not associated with significant irritation or sensitization at cosmetic levels.
Origin & sourcing
It is produced by neutralizing citric acid with a sodium base such as sodium hydroxide or sodium carbonate, giving the corresponding sodium salt. The citric acid starting material is itself manufactured at scale, today largely by fermentation, making sodium citrate a widely available, well-characterized ingredient.
History
Sodium citrate is a long-established compound carrying the food additive designation E331 and a Generally Recognized As Safe (GRAS) status from the U.S. FDA. It has a documented history as a blood anticoagulant, working by binding calcium ions, which reflects the same metal-binding behavior exploited in cosmetic and food formulations.
Questions everyone asks
What does sodium citrate do in a sunscreen?
It buffers and adjusts the product's pH and binds stray metal ions from water, helping keep the formula stable over its shelf life.
Is sodium citrate the same as citric acid?
It is the sodium salt of citric acid. Where citric acid is acidic, sodium citrate is used to balance and stabilize pH and to bind metal ions.
Is sodium citrate safe on skin?
Yes. It is a mild, well-tolerated ingredient used at low levels, and the same compound is recognized as safe in food by the U.S. FDA.