Scratch your head; but don’t draw blood! If you see white under your fingernails, you have scratched off sebum. A gland next to our hair follicles produce sebum naturally as a method for helping to protect the hair itself and the scalp. Sebum is a waxy ester; similar to ear wax (ew, I know). When you strip off the subum, you are destroying the scalp’s natural defense mechasim.
If you don’t have subum most likely you are washing your hair too much. Try to wash your hair less. In the past people would wash their hair only once a month or every two weeks. To clean their hair they would brush their hair daily with a boar’s hair brush or another natural bristle brush. The brush helps clean any debris out of your hair and redistrubutes the natural oils.