Billye,

I don't know anything about Science Diet dog food.... but your comment about the vet saying it might be allergy based made me remember something..

I had a cat that was allergic to fish. It took FOREVER to figure it out because almost all cat food has some sort of fish product in it. We finally figured it out when we went on vacation and the cat stayed at a kennel for a weekend and the food the kennel served had no fish product and the cats hives went away.

Animals can have some strange allergies.... and unfortunately allergy testing on pets is a lot harder than allergy testing on humans.