TAKE YOUR CAT TO A VET. Nobody can diagnose a chronic skin condition over the internet with a few lines of text and a couple of poor quality pictures.
A lot of pet owners do not appreciate how difficult and expensive it can be to diagnose and treat a chronic skin problem. A full skin workup for a difficult case can easily run into several hundred pounds when you include skin cytology, fungal cultures, flea/lice/mite treatment, antibiotics, low allergy diet trials, allergy testing, skin punch biopsies, etc.
Things you can do at home to make your vet's job easier:
1) Go to a vet sooner rather than later - do not allow this to get worse, it is only likely to cost you more in the long run.
2) Make sure he is properly covered against ALL ectoparasites (not just fleas) - I personally would use Advocate. Frontline/Bob Martin's/Johnson's/etc are not in any way comparable.
3) Try a ultra low allergy diet trial (ie; Royal Canin Hypoallergenic, Hills z/d, Purina HA) - It will take 6-8 weeks to see if it has made any difference (again, better to start sooner rather than later) and more importantly you can only feed that food, no treats, no tidbits, no gravy to make it taste better...just that food.
4) Keep up your appointments to enable your vet to assess how well any treatments have worked and whether additional treatments/tests are necessary. A lot of people cancel repeat appointments when the skin starts to look better only to come back a couple of weeks later (after a prolonged break in treatment) to find it as bad as it was in the first place (or worse).
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