What does sulfate free mean?

Sulfate is a chemical used in many hair care products that primarily causes the foaming action commonly associated with shampoos. Sulfate when used in abundance may cause some side effects for the sensitive skin, such as redness, dryness and itching. Most Balmain Hair products are sulfate free, but the sulfates that are used in some of the Balmain Hair Couture products are not harmful to humans or the environment. The sulfate free formula maintains the natural oils on the hair and scalp, which leaves your hair moisturized.