Cosmetic additive (4)
I believe the answer is:
aloe
'cosmetic additive' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aloe that I've seen before include "Fleshy-leaved plant" , "Plant source of purgative drug" , "Bitter drug from a leaf juice" , "Flower, maybe vera" , "Succulent plant (may be bitter!)" .)