#1 a cold sore is Herpes, have you been exposed to Posion Ivy? if it was herpes it would be a blister with clear fluid, (similar to the ones you see on your ankles when you wear a new pair of shoes) it would burn and itch, then once it pops, it becomes a sore with a scab, my best advice would be to go and have it cultured, while it is still there, that way you will know for sure.....