Unwanted breakout (4)
I believe the answer is:
acne
'unwanted breakout' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for acne that I've seen before include "Youthful problem" , "Skin problem, mainly of teenagers" , "Face problems" , "Skin condition associated with pimples" , "(Inflammation causing) spots" .)