Not good to get covered in day cream formulation for rash (5-3-4)
I believe the answer is:
devil-may-care
'rash' is the definition.
(thesaurus)
'not good to get covered in day cream formulation' is the wordplay.
'not good' becomes 'evil' (evil is the opposite of good).
'to get covered in' means one lot of letters goes inside another.
'formulation' is an anagram indicator (a formulation or mixture of the letters).
'day'+'cream'='daycream'
'daycream' is an anagram of 'dmaycare'.
'evil' put within 'dmaycare' is 'DEVIL-MAY-CARE'.
'for' is the link.
(Other definitions for devil-may-care that I've seen before include "Cheerfully reckless" , "Reckless, audacious" , "Reckless - mediaeval cry (anag)" , "Negligent" , "Insouciant (attitude)" .)