Old city Italian backed against ancient region ... a rash result (9)

'a rash result' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'old city italian backed against ancient region' is the wordplay.
'old city' becomes 'ur' (ancient city state).
'italian' becomes 'it' (abbreviation for Italian).
'backed' shows that the letters should be reversed in order.
'against' is a charade indicator (letters next to each other).
'ancient region' becomes 'caria' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'it' written backwards gives 'ti'.
'ur'+'ti'+'caria'='URTICARIA'

Can you help me to learn more?