Tetracycline target (4)
I believe the answer is:
acne
'tetracycline target' 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 "Skin problem, mainly of teenagers" , "Pimply skin condition of adolescence" , "Adolescent spots" , "(Inflammation causing) spots" , "Spotty skin condition" .)