Hello, I'm Dr. Deb.
I recently came online and see that your question about Mange hasn't been answered. I'm so sorry that you've had to wait for a response,but if you still need assistance, I'd like to help if I can.
When presented with a cat who has a chronically itchy face/chin, then I'd want to rule out food allergies before anything else. If this is the problem, until or unless the food is changed, the problem will continue despite various drugs and medications.
Sometimes this can be a trial and error process (finding a food which the patient will eat and which is also effective) since testing for food allergies is not always the easiest thing to do. There are blood tests which can be done but they aren't terribly accurate.
Food allergies are usually to ingredients in the cat food which a cat has been eating for a while--it's not typically to new food as you might expect.
I'm not sure what options you have in Ireland when it comes to cat foods, but the following are what I usually recommend:
Changing to a hypoallergenic diet may be helpful such as grain-free, or Z/D (a prescription diet which should be available from your vet) or Natural Ba***** *****mited Ingredients, Nature's Variety Instincts line, Evo Duck or Venison, Nature's Variety Frozen Raw Medallions (I recommend that they be zapped in the microwave for 10-15 seconds on each side).
It can sometimes take 1-2 months to know whether or not the food you've selected will be effective.
I hope this helps although, again, my apologies for the delayed reply. Deb