'auto-reactivity' is built from the prefix 'auto-' and the noun 'reactivity.' 'auto-' originates from Greek 'autos,' meaning 'self,' and 'reactivity' comes from the verb 'react' (from Latin elements 're-' meaning 'again' and 'agere'/'act' meaning 'to do or act'), with the noun-forming suffix '-ivity'.

'react' entered English via French 'réagir' and Latin roots 're-' + 'agere.' The adjective 'reactive' and the noun 'reactivity' developed in English; in modern scientific usage the prefix 'auto-' was attached to create 'autoreactivity' or hyphenated 'auto-reactivity' to denote self-directed reactivity.

Originally related more generally to the idea of 'reacting' (acting in response), the combined form 'auto-reactivity' has specialized in biomedical contexts to mean 'reactivity directed against one's own tissues or molecules.'