Just at ulcer site. Cold sores on the lips or near the lips, are usually caused by recurrent oral herpes virus. They start as a slightly raised reddish area, with a bit of numbness & tingling there. Then comes a cluster of tiny blisters, which break open soon, with some pain; leaving a sore (ulcer) to heal up over a week. Sores appear more often when one is under stress or is ill from another illness.