The most common cause of roseola is the human herpes virus 6, but the cause also can be another herpes virus — human herpes virus 7.

Like other viral illnesses, such as a common cold, roseola spreads from person to person through contact with an infected person's respiratory secretions or saliva. For example, a healthy child who shares a cup with a child who has roseola could contract the virus.

Roseola is contagious even if no rash is present. That means the condition can spread while an infected child has only a fever, even before it's clear that the child has roseola. Watch for signs of roseola if your child has interacted with another child who has the illness.

Unlike chickenpox and other childhood viral illnesses that spread rapidly, roseola rarely results in a communitywide outbreak. The infection can occur at any time of the year.

Jun. 29, 2012