An exanthem is a widespread rash built from repetitive lesions: the same kind of lesion repeated across much of the body rather than confined to one region. The classic childhood exanthems are the illnesses in which that rash is the clearest and most characteristic symptom, rather than an incidental finding during some other illness.
Six were numbered in a historical sequence — measles, scarlet fever, rubella, fifth disease, roseola infantum and varicella. The fourth slot in that sequence (Duke’s disease) has since been discarded, and the numbering is no longer used clinically, but the group survives because it is genuinely practical: it covers the febrile rashes a child is most likely to present with, where the decision is whether the illness is self-limited (resolves on its own) and can be managed at home or whether it needs a swab, an antibiotic, isolation, or admission.
These six are grouped by that clinical situation rather than by mechanism, and their causes are unrelated: several different viruses and one bacterial exotoxin (a toxin released by the bacterium). The member that behaves differently is scarlet fever, which is the only bacterial classic, the only one confirmed with a swab, and the only one that requires antibiotics.
Choose a route through this family
Because the six share a clinical situation rather than a cause, the place to start, if the topic is new, is what they have in common: how a rash is described and how the field is narrowed. Two notes supply that vocabulary of lesion morphology (the type and shape of the individual spots) and the age bands that the disease notes assume.
- Overview and Classification of Childhood Exanthems: what exanthems are, how they are produced, how they are classified by lesion, and the six classics in a single table.
- Diagnostic Framework for Childhood Exanthems: the four axes of exposure, age, season and rash characteristics, and the side-by-side differential across the six.
After that, each disease note takes one illness in depth, and they can be read in any order.
- Measles: the most transmissible of the six, its three clinical phases, and the late neurological complication that appears years later.
- Scarlet Fever: a rash produced by a toxin rather than by infection of the skin, and why the full antibiotic course matters.
- Rubella: the mildest of the six, the lymph node enlargement (lymphadenopathy) that precedes its rash, and why it matters through the people who are not immune.
- Fifth Disease: a virus that targets a single cell type, the two-phase (biphasic) illness it produces, and the two populations it endangers.
- Roseola Infantum: the fever-then-rash signature of infancy.
- Varicella: the only vesicular (blister-forming) classic, and how to decide which children need antiviral treatment.
The complications note works best last, once the diseases are familiar, because it looks back across all six:
- Complications and Pitfalls of Childhood Exanthems: what each disease does weeks or years later, and the reasoning errors that matter most.
Where this family stops
The six classics are not the only causes of fever with a rash. Several others appear in the same differential but are deliberately not covered here: hand-foot-and-mouth disease, erythema multiforme, Kawasaki disease, rashes associated with Epstein-Barr virus, and drug eruptions, including the severe forms with mucosal involvement and epidermal detachment (Stevens-Johnson syndrome and toxic epidermal necrolysis). Each has a different mechanism and belongs to a different topic. Congenital and maternal infections of the rubella, varicella and parvovirus families are treated elsewhere as well: this family covers the childhood illness, and mentions maternal-fetal consequences only where they change how a childhood case is managed.