'allergenicity' originates from 'allergen,' which comes from the Greek word 'allergia,' meaning 'other work.'

'allergia' transformed into the French word 'allergène,' and eventually became the modern English word 'allergen' with the suffix '-icity' to denote the quality or state.

Initially, it meant 'the quality of causing an allergic reaction,' and this meaning has largely remained the same in modern usage.