Many people take soap for granted. We know it works, but we don't know why. We base our purchasing decisions on brand names and price more than we do on ingredients, and who can blame us? Trying to read the ingredients on the back of a shampoo bottle can be like trying to read a foreign language for the first time. But if you tried, you might find tetrasodium EDTA mixed in with all those other hard-to-pronounce chemical compounds. It's a common ingredient in cleansers such as shampoo and hand soap, and you'd have a hard time getting clean without it. Tetrasodium EDTA is used as a chelating agent, or to put it in layman's terms, it makes hard water become soft. As water makes its way through the water cycle, it sometimes picks up metal ions such as calcium and iron. These metal ions can make water hard, which is a problem because hard water won't get you clean. Body washes, shampoos and other cleansers work as surfactants, which are responsible for attracting dirt and oil and pulling it off your skin so it can be rinsed away by water. The only problem is that surfactants also attract the metal ions found in hard water, hindering the surfactants' ability to cleanse your skin. That's where tetrasodium EDTA comes in. As the chelating agent, it neutralizes the metal ions in hard water and allows the surfactant to do its job. The end result is soft water and squeaky clean skin [source: Parbhoo].

Whitmore, Elizabeth.  "How does tetrasodium EDTA work in cleansers?"  20 August 2009.  HowStuffWorks.com. <http://health.howstuffworks.com/skin-care/cleansing/products/tetrasodium-edta-in-cleansers.htm>  01 October 2010.