Disodium Phosphate, also known as disodium hydrogen phosphate or sodium hydrogen phosphate (with the chemical formula Na2HPO4), is derived from the combination of phosphoric acid (H3PO4) with soda ash. Once crystallized and purified, it is used in various skincare products. The question that arises is: what is the purpose of disodium phosphate? Here's what you need to know about this ingredient.