Hi, I Have A Hard Patch Of Scalp At The

Hi, I have a hard patch of scalp at the back of my head, if I scratch it, it will peel away, it seems to gather right around my hair...it itches bad, when I sweat, but other than just being there, I don't really notice it. But it's white, hard and chunky.....I don't like it, what can I do? what might it be?