Human Herpesvirus 6 (HHV-6) is a virus that belongs to the herpesvirus family. It is known to cause roseola, a common childhood illness characterized by a high fever followed by a rash. There are two variants of the virus: HHV-6A and HHV-6B, with HHV-6B being the primary cause of roseola in infants. HHV-6 is widespread, and most people are infected by the age of two. After the initial infection, the virus remains dormant in the body and can reactivate later in life, potentially leading to complications in individuals with weakened immune systems.