According to About.com, eliminating sulfates in shampoo can reduce the risk of irritation to skin, scalp and eyes. Sulfates also damage the hair follicle, which can lead to diminished hair growth or weakened hair structure. Although there is an urban legend that sodium lauryl sulfate causes cancer, the U.S. Food and Drug Administration has not banned it from shampoos or cosmetics.
Sulfate-free shampoos help avoid the brittleness and hair breakage that sulfates can produce, as well as helping to maintain hair volume since fewer hairs fall out during shampooing. Sulfate-free shampoos are gentle on color-treated hair, prolonging the longevity of the hair coloring. In addition, sulfates strip oil from hair; without them in shampoo, hair curls less and is smoother and less frizzy after shampooing.
Sodium lauryl sulfate is put in shampoo to make it foamy when shampooing. Without sulfates, shampoo cleans just as well but does not create much lather. Although sulfates have not been proven to be carcinogenic, they are absorbed by the liver and mimic the behavior of estrogen.
The main drawback of sulfate-free shampoos is that, as of 2014, they are more expensive than shampoos that contain sulfates. Nevertheless, the perceived health benefits are such that many shampoos with no sulfates label themselves as "sulfate-free" on their packaging.