Worth occasionally going into Spar to get beauty product (5)
I believe the answer is:
botox
'beauty product' is the definition.
(Botox is used for cosmetic purposes)
'worth occasionally going into spar' is the wordplay.
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
'going into' means one lot of letters goes inside another.
'spar' becomes 'box' (I've seen this in another clue).
The alternating letters of 'worth' are 'ot'.
'ot' placed inside 'box' is 'BOTOX'.
'to get' acts as a link.
(Other definitions for botox that I've seen before include "(Temporary) anti-wrinkle treatment" , "poisonous cosmetic" , "It's used to smooth wrinkles, temporarily" , "Agent removing lines" .)