Hello. Thanks for writing to us at heathcaremagic The pimple/bump on your back is most likely a sebaceous cyst, which are accumulations of thick, yellow, putty material. The material that is stored in the cysts is actually derived from the sebaceous glands which are present in lining cyst wall. The cyst may stay as it is for years Or may grow ever so slowly as the secretions accumulate. Occasionally it may become secondarily infected with bacteria and then may become painful and bigger in size. Infection would require oral antibiotics. Treatment of cyst is surgical, wherein the cyst is removed in entirety, along with its wall. If some part of cyst or wall is left over, the cyst may recur. I would suggest that you visit a dermatologist or a surgeon in your region for the needful. Regards