I had a Aussie that was allergic to certain types of food. Most dog food if you look at the label start with corn as the first ingredient, my vet told me that was not good... Should start with some type of meat. He advised us to take him off of dog food and start adding foods back to see if that would help it did. some dogs are allergic to grass. my daughter's Boston terrier had to take steroids to stop the itching