Answer
Keratinized cells, as those in hair, are dead and are not easily modified.
Work Step by Step
Application of protein to the hair can change its feel, but simply touching protein to the hair is not sufficient. Keratin treatments for hair involve a lengthy application of protein along with other chemicals and heat treatments to alter the hair shaft. A protein shampoo would not be very effective since the protein would only briefly be in contact with the hair before the majority would be washed off. Additionally, the accessory chemicals needed to create a greater impact would not be present in a shampoo.
