Most genuinely felt insect repellent reduced irritation (7)
I believe the answer is:
deepest
'most genuinely felt insect repellent reduced irritation' is the definition.
I can't judge whether this defines the answer.
'insect repellent reduced irritation' is the wordplay.
'insect repellent' becomes 'deet' (I've seen this in another clue).
'reduced' means to remove the last letter.
'irritation' becomes 'pest' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'deet' with its final letter removed is 'dee'.
'dee'+'pest'='DEEPEST'
Can you help me to learn more?
(Other definitions for deepest that I've seen before include "most insidious" , "Of the greatest depth" , "hard to get, in the extreme" , "Most profound" , "most hard to fathom" .)