Herpes simplex is a virus that causes skin infections. The infection lasts your lifetime, and it causes painful or itchy sores and blisters that come and go. Herpes simplex virus typically doesn’t cause severe problems. But it can be dangerous in infants and people with weakened immune systems. There are two types of herpes simplex: Herpes simplex 1 (HSV-1, commonly known as oral herpes) tends to affect your mouth or face. It causes cold sores. HSV-1 spreads through contact with saliva (spit). Herpes simplex 2 (HSV-2, commonly known as genital herpes) is a sexually transmitted infection (STI). It causes sores on skin that comes in contact with the genitals of an infected person. Sometimes a herpes infection can affect other parts of your body, such as your eyes or other parts of your skin.