Fever blisters are caused by the herpes simplex type I virus and result in painful fluid filled lesions that eventually rupture and crust over. These lesions can affect the oral mucosa inside the mouth in addition to the lips.
In healthy patients, these lesions are self limiting and resolve in 7-10 days without treatment. However, if treated in the prodromal stage before the lesions erupt, some lesions can be aborted and others will be less severe and resolve sooner than 7-10 days.
Medications used to treat fever blisters are either topical ointments or are oral medications that are swallowed. Again, they are only effective in the very early stages of the lesions.
Once you have fever blisters, the virus resides in your nerve endings forever and can be activated by stressful situations, sun exposure, and by trauma. Be sure to tell your dentist or oral surgeon that you have had fever blisters in the past before any dental or oral surgery procedures. Measures can be taken to minimize or prevent them from occurring after a procedure.