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Roseola (roseola infantum) is a mild illness caused by a virus. It is generally harmless and is most common in children 6 months to 2 years of age. It is rare after age 4. Roseola is caused by two common viruses.
âHives virusâ is a term used to describe any virus which causes someone to break out in hives during or after the illness. Some viruses, such as roseola, are commonly associated with hives and other rashes.Others, like the common cold, can also lead to rashes in those who are hypersensitive.oseola is one type of hives virus which can cause welts and a skin rash after infection. It is most commonly noted in children. This virus can cause high fever, nausea, and cold-like symptoms for several days.