Koplik spots (also Koplik's sign) are a prodromic viral enanthem of measles manifesting two to three days before the measles rash itself. They are characterized as clustered, white lesions on the buccal mucosa (opposite the upper 1st & 2nd molars) and are pathognomonic for measles. The textbook description of Koplik spots is ulcerated mucosal lesions marked by necrosis, neutrophilic exudate, and neovascularization. They are described as appearing like "grains of salt on a wet background", and often fade as the maculopapular rash develops. As well as their diagnostic significance they are important in the control of outbreaks. Their appearance, in contacts of a diagnosed case, before they reach maximum infectivity, permits isolation of the contacts and greatly aids control of this highly infectious disease.