Roseola (also known as sixth disease, exanthem subitum, and roseola infantum) is a viral illness in young children, most commonly affecting those between the ages of 6 months and 2 years. It is typically marked by several days of high fever, followed by a distinctive rash just as the fever breaks.

Two common and closely related viruses can cause roseola: human herpesvirus (HHV) type 6 and possibly type 7. These two viruses belong to the same family as the better-known herpes simplex viruses (HSV), but HHV-6 and HHV-7 do not cause the cold sores and genital herpes infections that HSV can cause.

A child with roseola typically develops a mild upper respiratory illness, followed by a high fever (often over 103° Fahrenheit, or 39.5° Celsius) for up to a week. During this time, the child may appear fussy or irritable and may have a decreased appetite and swollen lymph nodes (glands) in the neck.

The high fever often ends abruptly, and at about the same time a pinkish-red flat or raised rash appears on the child's trunk and spreads over the body. The rash's spots blanch (turn white) when you touch them, and individual spots may have a lighter "halo" around them. The rash usually spreads to the neck, face, arms, and legs.