I'd suggest doing a salmon oil supplement, I've seen dogs with yucky skin have great improvement with it. That being said, there are SO many things that dogs can be allergic to, who is to say food even has anything to do with it. I'm a groomer and have seen so many dogs with weird allergies... grass is extremely common, we have a dog that comes in that is allergic to carpet, another allergic to humans, another allergic to the cat, and used to do one allergic to the sun... so I would suggest spending the big bucks and having allergy testing done (same way they do it for humans) and just finding out, so you don't have to waste a bunch of time, energy and effort into playing a guessing game. Good luck! These things can be really frustrating! lol