As a guy, I watched a video from a guy who stopped using shampoo, and I've stopped using shampoo. Ten years later, I still have good hair, I don't look like Huckleberry Finn, and I have no dandruff problem anymore.
The guy was saying: "You use soap to remove oils that your head's skin produces so your hair and skin would be ok, so your head gets too dry, then your skin produces more oils, so you have oily hair, you wash it, so your skin gets too dry, so you wash it..." - Well, for the first month I didn't look well, but then my head returned to some balance and its alright since. I wash my hair with water, intensively massaging my head, I do it several times in between of washing the rest of my body (I do use soap or a shower gel). My hairs are nice, and my head feels nice, so fuck shampoo.
P.S. If you don't wash yourself enough, don't tell me that I recommended anything, tou have to wash, and quite often, depending on your sweating levels and everything.