Well, oops. In that case, I'd do allergy testing rather than trying food after food, but then I have no patience. I've only ever had one dog I suspected of allergies, and she isn't a picky eater, just had constant hot spots from itching. An adult dog can stand the temporary imbalance of an elimination diet, but again, I have no patience. So I had the blood allergy testing done, which I know a lot of people don't think is reliable, but a friend who has had several dogs with allergies recommended it to me. (They're usually food sensitivities, not real allergies I understand, but since it causes much dog misery, they need handling.) My friend did say that she didn't recommend testing from the place people here in Colorado would tend to use as she'd tried them and the results were not "duplicable," by which she meant if you sent blood from the same dog to them a year later you got different results and of course they were less helpful. She recommended Spectrum Labs
so I used them. My vet had never done such a thing before but drew the blood and sent it off.
It's expensive, but I was fortunate to be able to afford it, and as I said I'm not patient. The results for my girl were worth it. Her food sensitivities were to pretty much all the common dog food ingredients other than meats, which left me unable to find a kibble that didn't have something on her list. So I ended up going to a raw diet. Once I did that, she went from constant hot spots, sometimes 2 or 3 at a time, to 1 or 2 a year. And that was just with adjusting diet. The test also showed some some environmental allergies but thank goodness not to things like household dust or others that would be horrible to try to deal with. I've pretty much ignored the environmental ones, and still she's much better.
Now and then I do come across something Spectrum didn't test for that shows a reaction. For instance, after all the hoopla about coconut oil, I tried adding some of that to her diet. She started itching immediately. At least when that happens, you know what caused it.