If your nape and shoulders are developing an itch, it is because you do not rinse off your shampoo thoroughly.

1) If using a strong shampoo, after applying it to your hair rinse off immediately. Do not let the shampoo stay in your hair while you lather the rest of the body with soap as though in a shampoo commercial
2) Rinse your hair while you are facing the shower head.
3) Rinse your hair with your back turned to the shower head.
4) Rinse your hair with your left side turned to the shower head.
5) Rinse your hair with your right side turned to the shower head.