My JPop did this a couple weeks ago. The vet called it a "hot spot". Bacteria affects the area due to them licking and the hair staying moist. He cut the hair around the area
, gave him a shot and some cream to put on it. It was a type of cortisone for itching. From comments made on this board, if caught soon enough, you can treat it with neosporene (sp). Good luck, just don't let it go too long.