Herpes is caused by infection with the herpes simplex virus (HSV). In or around the mouth or genitals, it causes mouth sores or blisters, as well as other symptoms. When a person catches HSV, they are infected for the rest of their lives, though some people never show symptoms. Symptoms of the HSV type are present if they emerge. Herpes has no cure, although treatment can help manage symptoms and minimize the chances of recurrence.