Irritation produced by 'arness (4)
I believe the answer is:
itch
I believe this clue is a double definition.
'irritation' is the first definition.
(thesaurus)
''arness' is the second definition.
('hitch' - thesaurus - said with the 'H' dropped, a cockney accent, like 'harness' was)
'produced by' is the link.
(Other definitions for itch that I've seen before include "Irritating sensation on skin" , "Desire; irritation" , "source of irritation" , "A strong restless desire" , "Irritate" .)