I Have A Small Numb Spot On My Scalp, About

I have a small numb spot on my scalp, about half an inch. I keep pulling hair out of this one spot till one day I looked in the mirror and the spot was bald. I can't feel anything in this little spot and it feels like there is an indentation. I can feel the numbness is slowly spreading from this little spot. What is this? It's annoying because since its numb I want to keep pulling hair out