One covering end of chin in spots (4)
I believe the answer is:
acne
'spots' is the definition.
(I've seen this before)
'one covering end of chin' is the wordplay.
'one' becomes 'ace' ('ace' can be a synonym of 'one'**).
'covering' is an insertion indicator.
'end of' indicates one should take the final letters.
The last letter of 'chin' is 'n'.
'ace' placed around 'n' is 'ACNE'.
'in' is the link.
(Other definitions for acne that I've seen before include "Adolescent spots" , "Skin condition prevalent among teenagers" , "Inflammation of glands in skin" , "Skin disorder" , "Skin problem, mainly of teenagers" .)