A person with Herpes simplex has an infection with Herpes simplex virus type 1 or Herpes simplex virus type 2. Both viruses cause recurrent episodes of painful blisters on the skin surface.

Herpes simplex virus can be divided into two basic types.

Herpes simplex type 1
Herpes simplex type 1 causes an oral rash (cold sores) in 80 percent of the cases, and a genital rash (genital herpes) in 20 percent of the cases. Herpes simplex type 1 is spread via infected saliva. About 80 percent of adults in the US are infected with Herpes simplex type 1, but only 30 percent of these adults experience episodes of rash.

Herpes simplex type 2
Herpes simplex type 2 causes a genital rash in 80 percent of cases, and an oral rash in 20 percent of cases. Herpes simplex type 2 is a sexually transmitted disease. About 25 percent of adults in the US are infected with herpes simplex type 2, but only about 20 percent of these adults experience episodes of rash.