Disodium Phosphate

Disodium phosphate is primarily a pH buffer/chelating-support salt used at low concentrations (typically well under 1%) to stabilize formulations and maintain efficacy of other ingredients. In rinse-off and leave-on cosmetics, it is generally well tolerated with low rates of irritation in patch testing, but as an alkaline buffering salt it can cause mild stinging or dryness in highly compromised skin if it shifts product pH or is used around irritated areas. For patient safety in eczema-prone populations, I score it as very gentle but not fully inert. Safety Notes: Disodium phosphate is most commonly used as a pH adjuster/buffer and chelating-supporting salt in water-based skincare, where it often appears at very low levels (around 0.01–0.1%) in leave-on lotions/serums and rinse-off cleansers to stabilize pH alongside other phosphates. Higher consumer-available levels are seen in strongly buffered systems (e.g., some cleansers, exfoliating/neutralizing systems, and specialty formulations needing higher ionic strength), where total use can reach ~1–3% without being prescription-only. The same broad range applies to leave-on vs. rinse-off products, but rinse-off formulas are more likely to sit at the upper end due to better tolerance of salts and buffering load.