Ever wondered where the word allergy comes from? In 1906, Austrian Pediatrician Clemens von Pirquet first used the word allergy to describe the strange, non-disease related symptoms that some diphtheria patients developed when treated with a horse serum antitoxin. The word comes from the Greek word 'alol', meaning, 'change in the original state'. And aptly, an allergic reaction is the result of the body's change when it adversely responds to a harmless substance. Pirquet is also the father of the modern tuberculosis test, which is named after him.

Source: Encyclopedia Brittanica Online