Spies blemishes on skin (5)
I believe the answer is:
moles
I believe this clue is a double definition.
'spies' is the first definition.
(mole is a kind of spy)
'blemishes on skin' is the second definition.
(Other definitions for moles that I've seen before include "Burrowing animals or small growths on skin" , "Small dark spots on the skin" , "Traitorous spies" , "Skin spots or burrowing animals" , "Breakwaters" .)