Human herpesvirus 6 (HHV-6) is one of the eight known viruses that are members of the human herpesvirus family. The Human herpesvirus 6 is a virus within the Betaherpesvirinae subfamily of the genus, Roseoloviruses. There are seven other types of viruses in this family. HHV-6 has two known variants: HHV-6A and HHV-6B. Although the two variants are highly distinctive, diagnostic tests are usually unable to distinguish the specific culprit of an infection. The virus makes its home in almost 100% of the human population all over the world. While HHV-6A has not been linked to any diseases, HHV-6B is the cause of the common childhood illness, exanthem subitum (also known as roseola infantum or sixth disease), a near-universal childhood disease and other febrile illnesses.