Rash symptom (4)
I believe the answer is:
itch
'rash symptom' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for itch that I've seen before include "It must be scratched" , "Nagging wish" , "Feel tingling sensation in skin" , "Irritating pain" , "cause irritation" .)