Intradermal skin testing done by a veterinary dermatologist is the most accurate method to identify environmental allergies. Food allergies are rare, the dermatologist told me I could skip the blood test (specific to my dog’s treatment)
The ingredients you have mentioned are impossible to avoid, unless you consult a veterinary nutritionist and have a special made diet recipe. A lot of cross contamination goes on in dog food manufacturing plants.
It may be best to find a vet that you trust and work with him.
Ps: There is no cheap way out of this. Environmental allergies are complicated, there are effective treatments, they tend to be lifelong.
