Tetrasodium EDTA ethylenediaminetetracetic acid
CAS 60-00-4 fine white water soluble powder
It is added to cosmetics, including shampoos and soaps to work in synergy with preservatives and to improve product stability. It does this by chelation and sequestering, which, in short, means it prevents any material changes to products that might otherwise be caused by traces of mineral or metal in the ingredients. For this reason it is a very popular water softener.
Tip - if you find yourself desperately needing to manufacture without pure water then this is a good go-to product.