In fact shampoo will alter the pH level of your hair, so to put your hair back to an acceptable level a conditioner is required.
Shampoo is alkaline, while conditioner is acidic.
A common mistake made with the conditioning process is that the hair is not combed through after applying. This ensures that the roots are not covered, causing the hair to be weighed down. Then comb the conditioner through with a wide toothed comb, smoothing the cuticle flat avoiding a raised and fluffy appearance. Finally rinse well. If your hair looks and feels in poor condition use a protein treatment regularly, i.e. once a week.