herpes simplex
"Yesterday I felt the familiar tingle throbbing sensation and headed to my local drug store to buy a tube.  They were out but had a generic brand.  I passed and found another store that had Abreva. Although I didn't have a blister yet, I began using it right away and applied liberally.  Now 24 hours later I have no more signs of cold sore coming and no blister.  I think/hope I was able to stop it before it got started.  I think the key was to start using Abreva before a blister appears.  I have used it in the past after blister appeared and it did speed up healing time."