among physicians, the same with exanthema. See Exanthema.

in Chemistry, denotes the formation of a kind of mealy powder on the surface of certain bodies. Efflorescence is occasioned either by decomposition or drying. The efflorescence which happens to cobalt and martial pyrites is of the first; and that observed on the crystals of soda, Glauber's salt, &c. of the latter kind. An efflorescence is sometimes also a species of crystallization; such as the beautiful vegetations which shoot up from different saline substances. See Crystallization.