herpes simplex
"Felt a little numb on the top of my lip, so I ran to put some Abreva on it. I used it for about a day and a half as directed (5x daily) with quite a healthy amount each time. I realized after the day and a half that anywhere I put the Abreva, the cold sore had spread to and was now blistering. It did the exact opposite of what it said it was supposed to do. Will never use again."