Scrubbing away a sea sponge secretion (5)
I believe the answer is:
sebum
'secretion' is the definition.
(bodily secretion from sebaceous glands)
'scrubbing away a sea sponge' is the wordplay.
'scrubbing away' indicates named letters should be taken away (some letters get scrubbed or erased).
'sponge' becomes 'bum' (synonyms).
'sea' with 'a' taken away is 'se'.
'se'+'bum'='SEBUM'
(Other definitions for sebum that I've seen before include "oily stuff" , "Lubricant" , "Oil on skin and hair" , "Oily skin secretion" , "which will cover the skin" .)