An exanthem (from Greek "exanthema", a breaking out) is a widespread rash usually occurring in children. Exanthems can be caused by toxins or drugs, microorganisms, or can result from autoimmune disease.
It can be contrasted with an enanthem.
Historically, six "classical" infectious childhood exanthems have been recognized, four of which are viral. Numbers were provided in 1905.
The four viral exanthema have much in common, and are often studied together as a class. They include:
Scarlet fever, or "second disease", is associated with the bacterium Streptococcus pyogenes. (Measles and scarlet fever were distinguished in the 17th century.) Fourth disease, a condition whose existence is not widely accepted today, was described in 1900 and is postulated to be related to Staphylococcus aureus.
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:
Vaccinations now exist against measles, mumps, rubella (as a part of the MMR vaccine) and chickenpox.
Diseases of the skin and appendages by morphology