Powder of vital cosmetics (4)
I believe the answer is:
talc
'powder' is the definition.
(I know that talc is a more specific form of the action powder)
'of vital cosmetics' is the wordplay.
'of' indicates a hidden word.
'TALC' can be found hidden inside 'vital cosmetics'.
(Other definitions for talc that I've seen before include "Bathroom powder (abbr)" , "Perfumed drying powder" , "I may dust" , "Soft stuff" , "Fine powder" .)