The only time that I use shampoo is when I am going to shave my head. I heard that shampoo is completely unnecessary and your hair will adjust after you stop using it for a couple weeks. This seems to be true in my situation.
depending on the length of hair..
If you have shorter hair, less than 2 inches, it may be fine to go without shampoo or soaping.
But, I have longer hair on top for styling, so, it holds onto too much natural skin oil if I don't use soap.