Massage will reportedly cause irritation (6)
I believe the answer is:
needle
'cause irritation' is the definition.
(to needle is to annoy or irritate)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for needle that I've seen before include "spur" , "Item for sewer" , "Gramophone record stylus" , "Annoy - syringe" , "Annoy by continuous criticism; stylus" .)