Salem have been doing alot of self-grooming lately it's kinda worrying, he also scratches his face, neck and behind his ears alot and I saw a few bald patches on his face today (under his chin, near his mouth on the right side and a line on top of his head, next to his ear).
Question : Should I be seriously worried and take him to the vet? Or is it maybe a symptom of flea bite allergy, and using frontline is enough?

Some bald spot on the right cheek. There's another small bald spot on his chin and top of his head