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When cats itch it is caused by fleas 50% of the time, food 40% of the time, and all other allergies and problems ( inhalant seasonal allergy, mites, bacterial infection, etc) 10% of the time.
Fleas and food must be eliminated before thinking of tests for everything else.
Purchase a flea comb and comb ALL cats daily for 5 days looking for live fleas or the black flecks of flea dirt that looks like ground pepper. You cannot rule out fleas in cats by just looking under the hair. You must comb them. If you see any evidence of fleas on anybody....treat everyone.
Any of the prescription once-a -month products (Frontline, Advantage, Revolution) are effective. Remember though that they all work great for 3 weeks, well for four weeks, they do not work for 5 weeks. Treat all cats once every three weeks for at least 2 treatments. Do not waste your money on over the counter products, they do not work. Comb regularly after that and treat as indicated.
In the case of flea allergy, it is not the individual flea bite that they are scratching. When a flea allergic cat is bitten by a flea, they have a reaction that causes them to react everywhere.
To eliminate food as a possible source of the itching, the cat must go off all the things it now eats or has ever eaten. All cat foods, canned and dry, all table foods, and all treats. Read all the ingredients on the labels. Anything that is in any of those foods the cat cannot have during the trial. If there is chicken or poultry meal, it cannot have chicken. If there is corn, it cannot have corn. If there is fish, it cannot have fish.
For the 3-4 weeks the cat is going to be on the food trial, it is often easiest to use cooked meats, lunch meat, or strained meat baby foods. You can use whatever meat is NOT in your cat's current diet. Feed that exclusively for 3-4 weeks. If all signs resolve, we will need to find a more balanced maintenance diet.
To be effective you must be religious about this so that food as a source of the allergy is eliminated.
You can search <food allergy in cats> for additional information.
While you're doing the above you can explore the house and environment for anything your cat could be breathing in that it could be allergic to: XXXXX XXXXX the litter, potpourri, cleaners, carpet fresheners, plants in the house, fireplace or cigarette smoke, etc, These should be eliminated also.
Just a rule of thumb....flea allergy and inhalant (seasonal) allergies are very responsive to steroids (cortisone), food allergy is not.
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