Originally Answered: Very Itchy Cat?
I just wrote this for the dog section, but just substitute "dog" with "cat."
Almost always these problems are diet-related. Allergies are really a sign of immunity problems. Most of the immune system is located in the GI tract, where nutrients are absorbed (seen the DanActive commercial?). When you screw up its workings with non-nutritive dog "food" you see all kinds of problems. What I mean, are the filler ingredients you see in most commercial dog foods. These include corn products, wheat products, soy products, peanut hulls, sugar, colors, flavors, salt, beet pulp... I could go on, but I won't. You see many of these non-food ingredients in well-known, vet-recommended prescription foods. Why are those ingredients in dog food: they're cheap. CHEAP=CRAP.
My diet of preference, that rises far above any other is raw. Although domesticated for thousands of years, a dog's gut still works the same as the wolf. They have the acids, enzymes and flora that are designed to digest raw meat and bones. What they don't have are the enzymes to digest grains (wheat, corn, etc). A balanced raw diet will cure most, if not all of your dog's problems. I live in FL where we have a flea problem year round. In my house there are 7 cats and 3 dogs, non of which need treatment for fleas. They don't need any chemicals because they are so healthy, they repel fleas on their own. When I think how expensive raw diet is, I just think of how much I save on flea prevention and treatment. For info:
If you really have trouble with raw, here are some other suggestions. It's a cut and paste from another question that I answered some time ago:
Sometimes a meat and rice recipe will work, but some of the problems that you're having will respond better to a high-quality grain-free diet. All kibble, which is cheaper than canned or raw, must have grain, potato, or tapioca in it to hold it together. Potato would be cheaper than tapioca, and potato is better than grain.
HIgh-quality means that most of the ingredients are of HUMAN-GRADE quality. None of the recall products were human-grade. If it's not good enough for me, it's not good enough for my dogs.
The first ingredient should be a meat. It shouldn't be a meat by-product or a meal. Neither of these are human grade, nor can they be measured for there nutritional content. That's because the company cooks down a bunch of different animal parts that's different each time.
Don't get anything with wheat, corn, soy (or soybean oil), BHA, BHT, ethoxoquin, artificial flavors and colors, salt, sugars (including sucrose and fructose).
A lot of these poor-quality ingredients are cheap fillers, flavor enhancers, and preservatives. They offer a low source of nutrition, and weaken the immune system. That's what causes allergies. The only reason they're in the recipe is because they serve a purpose for the company, not to keep your dog healthy.
I suggest you read dog food labels carefully. Look at foods like Evo (made by Innova), Timberwolf Wild & Natural or Ocean Blue, Barking At The Moon (made by Solid Gold). They're more expensive, but they would seriously cut down on the allergies, which would mean less trips to the vet. I also suggest adding a cold-water fish oil, like salmon, krill, anchovy or sardine. This will help a lot with the ear problem and the yeast. You could also add probiotics and dygestive enzymes.
One product that has salmon oil, pre- and probiotcs, and digestive enzymes is Positive Health by Great Life. They also make an excellent food, but is expensive. Their website http://www.greatlife4pets.com
EDIT: Hill's/Science Diet is the company that has done a lot of research. What do you think they've concluded... that their products are the best. There's no regulation for that either, other than meeting AAFCO's crappy standards. If Hill's makes such a superior product, why do we keep finding our pets with urinary issues, stones, obesity, cancer, allergies, etc, when fed their diets? Read the ingredients (they're posted on line at http://www.hillspet.com . It's all filler... where's the food?
EDIT: I agree about Nature's Variety Instinct. I think it's one of the best canned foods available. Nature's Logic and Evanger's are very good, too.