Could you tell me what are fever blisters?

Herpes simplex 1 vir: Cold sores or fever blisters tend to develop when an individual has a fever but can also be triggered by sun exposure, emotional distress, intestinal illness and menstruation. These blisters can recur in the same spot or in different locations.A sore or blister will typically take a few days or a week to resolve. Caused by herpes simplex i virus and are highly contagious.