Roseola is a common, mild viral infection (virus) affecting children between 4 months and 4 years of age (most commonly 6-24 months). The symptoms of the illness may vary widely, and some children may not act or appear sick at all.

Roseola usually begins with a rapidly rising high fever (103˚ F [39.5˚ C] or greater) that can last for three to seven days. During this time, children may appear comfortable and happy or irritable, have swollen glands in the neck, runny nose, cold-like symptoms, mild diarrhea or a bulging "soft spot" on the head (fontanel).

After three to seven days, the temperature returns to normal and a rash appears. The rash consists of rose-colored raised dots (papules) or as a flat (macular) rash. It is mainly on the neck, stomach and back but can also appear on the arms and legs. The rash does not itch and can last for hours to days.