Trisodium EDTA is a salt of ethylenediamine tetraacetic acid, and is used in cosmetics and personal care products as a chelating agent with the ability to bind to metal ions (Wikipedia). This property allows Trisodium EDTA to assist in preventing the deterioration of formulas, maintaining clarity, protecting fragrance compounds, and preventing rancidity. It can also counteract the effects of hard water by binding to the metal ions and deactivating them, preventing their drying action by disabling the metals' ability to leave a residue on the skin or hair. Trisodium EDTA can also "form complexes with calcium, magnesium, and iron, which allows for better foaming and cleaning performance of cosmetics and personal care products" (CosmeticsInfo.org).
Trisodium EDTA is found in a wide variety of skin and hair care products, including moisturizers, skin care and cleansing products, personal cleanliness products, bath soaps, shampoos and conditioners, hair dyes, and hair bleaches. Trisodium EDTA is CIR approved.