Roseola (roseola infantum) is a mild viral illness that affects young children. When a child has roseola, he or she has a sudden high fever followed by a rosy-pink rash appearing mostly on the torso, neck, and arms.
Fever seizures may occur with this illness because of the rapid increase in a child's temperature. The fever tends to last 2 to 3 days. As a child's temperature gradually drops, the rash usually forms and lasts 1 to 2 days.
Roseola is contagious and is most common in children 6 months to 2 years of age. It is rare after age 4.