Good to cut hair in irritating condition (5)
I believe the answer is:
mange
'irritating condition' is the definition.
'mange' can be an answer for 'condition' (mange is a kind of condition). I'm unsure of the 'irritating' bit.
'good to cut hair' is the wordplay.
'good' becomes 'g' (abbreviation).
'to cut' means one lot of letters goes inside another.
'hair' becomes 'mane' (mane is a kind of hair).
'g' inserted into 'mane' is 'MANGE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for mange that I've seen before include "Skin disease of cats and dogs" , "Skin disease of mammals" , "veterinary problem" , "skin problem" , "may have to deal with this" .)