Temperature and skin infection? Rubbish! (5)
I believe the answer is:
trash
'rubbish' is the definition.
('trash' can be a synonym of 'rubbish')
'temperature and skin infection?' is the wordplay.
'temperature' becomes 't' (abbreviation).
'and' means one lot of letters go next to another.
'skin infection?' becomes 'rash'.
't'+'rash'='TRASH'
(Other definitions for trash that I've seen before include "Condemn" , "Dismiss as valueless" , "Refuse; wreck" , "Refuse, garbage" , "Garbage or nonsense" .)