Crossword Genius

Youth spotted this problem (4)

Ross

I believe the answer is:

acne

'this problem' is the definition.
(I have seen 'Youthful problem' mean 'acne' so perhaps 'problem' could also mean 'acne')

I cannot understand how the rest of the clue works.

(Other definitions for acne that I've seen before include "Spotty coverage" , "Adolescent spots" , "Pimply skin condition of adolescence" , "Skin disorder" , "sort of disease" .)

I've seen this clue in The Guardian.
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