Skin problem

My cat has bumps on the back of his neck which has spread to the area under his chin. He also has some at the base of his tail and on his cheeks. There is no pus present. They feel dry and scaly and he scratches the affected area. I thought it could be excema so I purchased hydrocortisone spray a day ago. I am trying to treat him at home since there is no infection or fluids present but I am becoming a little concerned since the scabby bumps are spreading. Does anyone know what his problem could be?

It could be ringworm.  Get him to the vet for a check up.  It could also be flea allergy.