In its broadest sense, the term exanthem refers to a widespread cutaneous manifestation of a systemic illness. In children, exanthems are most often the result of a viral infection and less often due to a bacterial infection or a drug reaction. The exanthem can be the initial sign of the illness, can appear as the illness is resolving, or even can appear once it has resolved. The eruption may or may not be pruritic and is usually accompanied by systemic symptoms such as fever, malaise, and headache. Some viruses, such as varicella and measles, trigger specific, well-recognized eruptions, while most viruses result in a nonspecific exanthem, making an exact diagnosis unlikely.

The classic childhood exanthems were numerically designated according to historical appearance in the early 1900s and include measles (first disease), scarlet fever (second disease), rubella (third disease), erythema infectiosum (fifth disease), and roseola infantum (sixth disease).

All have a viral etiology except scarlet fever, which is caused by group A streptococcus. Measles and rubella are encountered much less often today because of routine vaccination of young children; however, outbreaks still occur all over the world.

In addition to the classic childhood exanthems, this chapter will discuss the distinct, recognizable presentations of hand-foot-and-mouth disease, the Gianotti-Crosti syndrome, unilateral thoracic exanthem, and the nonspecific viral exanthems, which are clinical characteristics, but can have several viral triggers. The clinical presentation of exanthems associated with toxin-producing Staphylococcus and Streptococcus will also be presented.

Although exact identification of the infectious agent that has triggered a particular exanthem is not always possible, a definitive diagnosis may be critical, particularly for pregnant and immunocompromised patients in whom certain viral infections can have serious consequences. It is also important to distinguish viral exanthems from rashes caused by treatable bacterial or rickettsial infections and from hypersensitivity reactions to medications. Familiarity with the most common childhood exanthems can aid in prompt recognition, diagnosis, and appropriate management including counseling on avoidance of contact with at-risk persons.