Herpes simplex is a common viral infection. If you’ve ever had a cold sore or fever blister, you picked up the herpes simplex virus. Most cold sores are caused by herpes simplex virus type 1 (HSV-1). Other names for cold sores caused by HSV-1 are:
Herpes simplex viruses are contagious, even when you do not see sores.
A closely related herpes simplex virus, HSV-2, causes most cases of genital herpes. But either HSV-1 or HSV-2 can cause a herpes sore on the face or genitals.