Shingles. My Dad had one. He felt ill with a blister on his forehead and went to the doctor. He was fobbed off. Got worse, so went to A and E at Kings Hospital in London. This was in the late 1950’s. They sent him home after tests. They didn’t know either, but said it looked like shingles but had never heard of it on the head! Our family doctor was called everything explained, and the first thing he said was “Is it on your head?” Dad was flabbergasted but our doctor had been in the military and it is quite common in men, but not women. Dad had the scar for the rest of his life.