How do I know if my cat has food allergies?

natureutt78 asked:Mycat hasa very badandneurotic habbit ofscratching spots onhisbody until theybecome raw andbleeding. Usually it’s behind hisneck,orinfront ofhisear. Hisisa indoor healthy kitty (nofleas!). Myvet thoughtitwasringworm atfirst,butourcat tested [...]