An exanthem is a widespread rash occurring on the outside of the body and usually occurring in children. It is usually caused by a virus, but an exanthem can be caused by bacteria, toxins, drugs, other microorganisms, or as the result from autoimmune disease. The term exanthem is from the Greek. It can be contrasted with enanthems which occur inside the body, such as on mucous membranes.

Infectious exanthem

In 1905, the Russian-French physician Léon Cheinisse (1871–1924), proposed a numbered classification of the six most common childhood exanthems. Of these six "classical" infectious childhood exanthems, four are viral. Numbers were provided in 1905. The four viral exanthems have much in common, and are often studied together as a class. They are: Scarlet fever, or "second disease", is associated with the bacterium Streptococcus pyogenes. Fourth disease, also known as "Dukes' disease" is a condition whose existence is not widely accepted today. It was described in 1900 and is postulated to be related to the bacterium Staphylococcus aureus. In 1979 and 2001 a possible "seventh disease" was postulated following reports of a condition in Japan also referred to as acute febrile infantile mucocutaneous lymph node syndrome (MCLS). Many other common viruses apart from the ones mentioned above can also produce an exanthem as part of their presentation, though they are not considered part of the classic numbered list: