I thought the same thing about 'residue,' but it's there if you use hair products, sweat, etc. For me, I noticed a considerable difference. It made my regular shampoo and conditioner lather up even more than usual - that was a huge sign to me. My hair literally 'squeaked' clean after using the Neutrogena. The results were also instantly noticeable by others. My Mom could tell a difference before I even had a chance to tell her about it.