I think it depends on what you use as a pre-shampoo treatment. When I do a pre-shampoo, I apply oils to my scalp for a massage, and I may use a concoction with a heavy oil like castor oil on my hair. Now since I'm one of those pple who'd rather have nothing on my hair (except an aqua spritz of EOs and ACV) and who hates to have anything on the scalp, I have to use shampoo the morning following a pre-shampoo treatment.