Exanthem subitum

Exanthem subitum (meaning sudden rash), also referred to as roseola infantum, sixth disease and (confusingly) baby measles, is a benign disease of children, generally under two years old, whose manifestations are usually limited to a transient rash ("exanthum") that occurs following a fever of about three day's duration.

Until recently, its cause was unknown: it is now known to be caused by two human herpesviruses, HHV-6 and HHV-7, also called roseolovirus.

Despite the fact that it is occasionally called baby measles, it is caused by a different virus than that which causes measles, which is a more severe disease.

The name sixth disease stems from the fact that when diseases causing childhood rashes were enumerated, it was the sixth listed. The list of such diseases is:

1. measles, rubeola, 14-day measles
2. scarlet fever, scarlatina
3. rubella, German measles, 3-day measles
4. Duke's disease (caused by various viruses including coxsackievirus, enterovirus, or echovirus)
5. fifth disease (erythema infectiosum, slapped cheek syndrome), caused by Parvovirus B19
6. sixth disease (exanthem subitum, roseola infantum, rose rash of infants, baby measles)