Tetrasodium Ethylene Diamine Tetraacetate or Tetraacedic acid is a chelating agent used to bind up hard water ions and remove them from the hair. It helps to stabilize products and extend shelf life. Unfortunately, its a rather nasty thing. The OSHA required labeling says that anyone handling it should be very careful not to eat or smoke or drink so that "even minute amounts of it" won't be ingested. Anyone handling it is also supposed to wear protective clothing because it can be absorbed through the skin. Once absorbed, it gets stored in major organs such as the brain and liver. It's not known at what level its toxic. And unfortunately it's in EVERYTHING.... and the exposure is cumulative. It's in your shampoo, your conditioner, your hair gel, your aloe gel, your hand lotion, and a lot of other things. It's used so often that its now being classified a persistent environmental pollutant. We use so much of it in so many products that its polluting our water.