Balsam is the resinous exudate (or sap) which forms on certain kinds of trees and shrubs.
The exudate is a mobile to highly viscous liquid often containing crystallized resin particles.
Over time and as a result of other influences the exudate loses its liquidizing components or gets chemically converted into a solid material (i.e. by autoxidation).
The Balsam of Matariyya was a substance famous as a panacea among physicians in the Middle East and Europe during the Antique and Medieval periods.
In particular, Euphorbia latex ("wolf's milk") is strongly irritant and is cytotoxic.