Healing mild acne I developed (9)
I believe the answer is:
medicinal
'healing' is the definition.
(I've seen this before)
'mild acne i developed' is the wordplay.
'developed' indicates an anagram.
'mild'+'acne'+'i'='mildacnei'
'mildacnei' is an anagram of 'MEDICINAL'.
(Other definitions for medicinal that I've seen before include "Having healing properties" , "concerning drugs" , "Lily 15's invention" , "Good for you!" , "of a health-giving nature?" .)