A herpes blister is the typical symptom of a herpes simplex virus infection. During the course of typical herpes simplex symptoms, a blister or cluster of blisters will start small, expand with fluid, then break open and scab. The appearance of a herpes blister means the herpes simplex virus is on the surface of the skin: at this point herpes simplex is most contagious. Blistering occurs when the herpes simplex virus is being destroyed by the body's immune defenses.