Spots note inside card (4)
I believe the answer is:
acne
'spots' is the definition.
(skin condition causing spots)
'note inside card' is the wordplay.
'note' becomes 'n' (abbreviation).
'inside' is an insertion indicator.
'card' becomes 'ace' (ace is a type of playing card).
'n' inserted within 'ace' is 'ACNE'.
(Other definitions for acne that I've seen before include "Problem to face in" , "Skin problem, mainly of teenagers" , "Cane for the teenager?" , "Skin affliction" , "Skin condition prevalent among teenagers" .)