Herpes simplex virus 1 and 2, also known by their taxonomical names Human alphaherpesvirus 1 and Human alphaherpesvirus 2, are two members of the human Herpesviridae family, a set of new viruses that produce viral infections in the majority of humans. Both HSV-1 (which produces most cold sores) and HSV-2 (which produces most genital herpes) are common and contagious. They can be spread when an infected person begins shedding the virus. About 67% of the world population under the age of 50 has HSV-1. In the United States, about 47.8% and 11.9% are believed to have HSV-1 and HSV-2, respectively. Because it can be transmitted through any intimate contact, it is one of the most common sexually transmitted infections.