I have had this dark scab on my scalp since I was a child. It never itched and it never hurt. I've tried all sorts of medicated shampoos, and it only reduced build-up to a small thin layer. But the build-up would comeback and i decided to live with this, until recently. I had a pimple on the back of my head. When i tried to pop it and apply rubbing alcohol, I accidentally scratched the pimple. A couple weeks later the scratched pimple became a scab just like my other bump. I tried using dermarest medicated shampoo, but the build-up still comeback.