Scratching head, do something to relieve irritation (7)
I believe the answer is:
unction
'something to relieve irritation' is the definition.
I can't judge whether this defines the answer.
'scratching head do' is the wordplay.
'scratching head' means to remove the first letter (the word's head is removed).
'do' becomes 'function' (both can mean an event).
'function' with its initial letter taken away is 'UNCTION'.
Can you help me to learn more?
(Other definitions for unction that I've seen before include "Oiliness" , "Act of anointing someone as part of a rite" , "Ointment - (false?) sincerity" , "Salve" , "Religious rite of anointing with oil" .)