Eruption, or rash, means an outbreak, in a scattered form, upon the surface of the skin. The skin is usually raised and red, or it may be covered with scales, or crusts, or vesicles containing ﬂuid. Eruptions diﬀer in appearance: for example, the eruption of MEASLES is always distinguishable from that of CHICKENPOX. But the same disease may also produce diﬀerent eruptions in diﬀerent people; or in the same person in diﬀerent states of health; or even on diﬀerent parts of the body at one time.
Eruptions may be acute or chronic. Most of the acute eruptions belong to the exanthemata (see EXANTHEM): that is, they are bright in col-our and burst out suddenly like a ﬂower. These are the eruptions of SCARLET FEVER, measles, German measles (see RUBELLA), SMALLPOX and chickenpox. In general, the severity of these diseases can be measured by the amount of eruption. Some eruptions are very transitory, like nettle-rash, appearing and vanishing again in the course of a few hours. (See also SKIN, DISEASES OF.)