With oral herpes, the virus remains in a nerve called the trigeminal nerve. While in the nerve, it may stay permanently inactive or it may travel down the nerve to the skin or mucosal surface causing a recurrence of fever blisters. About half the people who have been infected with herpes have a few episodes each year. A distinct tingling or burning sensation may occur minutes to hours before blister formation. This is called the prodromal stage.
Research is ongoing to discover how the virus is triggered.
The immune system appears to be involved and several factors have been known to affect this. Emotional stress, fever, illness, injury, and sunlight have all been implicated in prompting a recurrence of fever blisters. There are presently no vaccines and no cures although vaccine research is ongoing. Once the blisters have occured, symptomatic relief can be obtained with ointments that numb the blisters or soften the crusts of the sores. But it is important that patients be careful during this time to avoid spreading the virus to others and to other sites on themselves.