Why do you need sulfate free shampoo?
Sulfates are detergents -- originally, they were harsh industrial detergents. Made from petroleum as a cheaper substitute for soap when vegetable oils were hard to come by, sulfates produce large amounts of foam. During the Great Depression, makers of everything from shampoo to toothpaste discovered that sulfates could produce foam like the bubbles in a movie star's bathtub for just a fraction of a penny.
Sulfates don't make your hair (or teeth or anything else) cleaner than natural substances like coconut oil or sunflower oil, but they do create a lot of lather. Generations of advertisements have taught us that lots of bubbles is equal to cleanliness.
In fact, sulfates can strip away the healthy natural oils of your hair and skin, leaving you with dry, porous, easily damaged hair. They're not great for the environment, either.
Mixtina shampoos and conditioners do not contain sulfates.