Sulfate

This is an image of a shampoo and a bottle of dish washing detergent… the same sulfate is circled in their ingredients list.

"You'd never dream of washing a good sweater with detergent. Yet most shampoos contain harsh detergents (sodium lauryl sulfate or laureth sulfate) that one also finds in dish washing liquid. They're great for pots and pans because they cut grease so effectively. Your hair, on the other hand, needs to retain some natural oils, which protect your hair and scalp. Stripping them away deprives the hair of necessary moisture and amino acids and makes it look dry and dull." - Lorraine Massey