Herpes-Simplex: Type 2 Herpes is a name that is used to describe several types of skin eruptions that are characterized by formation of blisters. The term embraces primarily two distinct disorders, herpes simplex and herpes zoster, both caused by viruses. Together, these "herpes" viruses are estimated to cause more human illnesses than any other group of viruses. Two types of herpes simplex are known. The first causes cold sores or fever blisters, which is an eruption of blisters that often occurs during the course of or after one of a variety of diseases that eventually cause fever (most commonly average colds, the flu, and pneumonia). The blisters usually appear around the mouth