HSV1, also known as Herpes simplex virus 1 or HHV-1, is a human virus known for causing cold sores. It is distinct from HSV-2 which causes genital herpes. HSV-1 extremely common; an estimated 3.7 billion people, or 2 out of 3 of the world population, under the age of 50 are infected. The virus is spherical and enveloped, enclosing a linear double stranded DNA genome. There are at least 74 predicted genes, but there may be as many as 94 putative open reading frames. HSV-1 typically replicates and sheds in the skin and mucous membranes, but it can also latently infect neurons.