Sodium Metaphosphate

Sodium metaphosphate is primarily used as a chelating/sequestrant and stabilizer in low concentrations, and it is not considered a classic irritant active like acids or retinoids. However, as an inorganic phosphate salt it can cause mild stinging or irritation on compromised barriers (e.g., eczema, post-procedure) at higher local exposure or in leave-on products, so it is best categorized as generally gentle but not completely inert. Given sensitive-skin safety considerations and limited robust human irritation datasets specific to this salt in cosmetics, a conservative 'gentle' score is appropriate. Safety Notes: Sodium metaphosphate (a polyphosphate chelating/sequestering salt) is most often used at very low levels (~0.01–0.3%) in mass-market cleansers, shampoos, soaps, and some emulsions to bind hard-water ions and improve stability/foam performance. In consumer-available specialty “water softener/chelant” or clarifying wash-type products (rinse-off) and some bath/cleansing concentrates, levels can be pushed into the low single digits, with the highest OTC examples observed around ~3–5% where solubility, ionic strength, and irritation/tackiness constraints typically become limiting (leave-on products rarely exceed ~0.5–1%).