Skin irritation appearing after tin found in grass (6)
I believe the answer is:
snitch
'grass' is the definition.
(both mean to inform on or betray)
'skin irritation appearing after tin' is the wordplay.
'skin irritation' becomes 'itch' (I've seen this in another clue).
'appearing after' is a charade indicator (letters next to each other).
'tin' becomes 'Sn' (Sn is the chemical symbol for tin).
'itch' put after 'sn' is 'SNITCH'.
'found in' is the link.
(Other definitions for snitch that I've seen before include "Inform on, tell tales" , "who tells on his classsmate?" , "Grass" , "Police informer" , "Steal; inform (on someone)" .)