There is an itchy spot in the middle of my back which causes untolerable itching and become black and now spreading more and more.. In the summer due to sweating it become itchy and sometime numbness is there. I am suffering  about 4-5 years from this problem.. I have taken many medicines and ointments  but it couldn't get cure. My father and grandfather also suffered with this same problem but their problem has cured itself. Plz suggest me what can I do.