Superficial cut restricts a beauty treatment (6)
I believe the answer is:
facial
'beauty treatment' is the definition.
(I've seen this before)
'superficial cut restricts a' is the wordplay.
'superficial' becomes 'facile' ('facile' can be similar in meaning to 'superficial').
'cut' means to remove the last letter.
'restricts' is an insertion indicator.
'facile' with its final letter taken off is 'facil'.
'facil' going around 'a' is 'FACIAL'.
(Other definitions for facial that I've seen before include "Beauty treatment for front of head" , "Beauty treatment for the visage" , "Beauty treatment, maybe mudpack" , "Type of beauty treatment" , "Cosmetic treatment" .)