How long does it take for a cold sore on your lip to develop?

Not long: In my experience they come on very fast. Usually there is some tingling or mild pain. Next a small pink bump shows up. By the next day it is a larger, red, fluid filled blister. If you ask your doctor for a prescription for acyclovir, Valtrex (valacyclovir) or Famvir you can take it at the first sign. Taking it right away will usually keep it from turning into an ugly fever blister. Also abreva helps (otc).