If it has been going on for more than 1 year/4 seasons and the dog has not shown improvement despite food changes, frequent bathing, etc and continues to suffer.
The allergens that the dog is responding to are probably environmental, impossible to avoid and not diet related.
If you use the search engine above on the forum home page and look up “allergies” you will find a lot of my posts and some articles that are very informative.
I suggest you consult a dermatologist/specialist as there are other reasons for the symptoms you describe other than food intolerances.
