Skin cream is only skin-deep (8)
I believe the answer is:
cosmetic
'skin-deep' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cosmetic that I've seen before include "Aesthetic rather than necessary, surgery perhaps" , "Preparation designed to beautify the body" , "Slap on the face" , "Substance for beautifying the face (8)." , "Facial application" .)