Face problem found in Isaac Newton (4)
I believe the answer is:
acne
'face problem' is the definition.
'acne' can be an answer for 'problem' (I have seen 'Youthful problem' mean 'acne' so perhaps 'problem' could also mean 'acne'). I'm not sure about the 'face' bit.
'in isaac newton' is the wordplay.
'in' says the answer is hidden in the clue.
'ACNE' can be found hidden inside 'isaac newton'.
'found' acts as a link.
Can you help me to learn more?
(Other definitions for acne that I've seen before include "Pimply ailment of adolescnce" , "Spotty complaint" , "Face problems" , "Problem to face in" , "Spotty skin condition" .)