Allergies are caused by what?

11 year old cat now has allergies? What caused it?

• My cat whom I've had since she was a kitten has developed some kind of allergy within the last 2 years. I've moved her around the country to many new /different homes and changed her diet over the years as well. She never seemed to have any problems until she moved into this house a couple years ago. Now she gets sneezing fits and sometimes sounds like she's breathing through a clogged nose. Her eyes are runny too. I feel miserable because I've had her so long and now this happened I feel like somehow I caused it. We don't use chemicals, she is on flea drops but is an indoor cat, she's eats Pet Promise food, We use the corn litter variety, and I've had her to the vet multiple times. Even a vacation didn't seem to help her. What could the problem be?

• Answer:

  I googled it, maybe you can check out some websites (if you haven't already). http://www.google.com/search?hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&hs=cc5&q=cat+has+allergies&btnG=Search