Spots: a card contains any number (4)
I believe the answer is:
acne
'spots' is the definition.
(I've seen this before)
'a card contains any number' is the wordplay.
'a card' becomes 'ace' (ace is a kind of card**).
'contains' means one lot of letters goes inside another.
'any number' becomes 'n' (I've seen this in other clues).
'ace' going around 'n' is 'ACNE'.
(Other definitions for acne that I've seen before include "(Inflammation causing) spots" , "Pimply skin condition of adolescence" , "Inflammation of glands in skin" , "Youthful problem" , "Adolescent spots" .)