I also would not suspect that this could help, but we noticed that he did not react to my sister' dog, that has a very strict diet (below) but was reacting to other dogs. So it made sense to try switching the diet before giving up on the dog.
Before my dog was getting a mix of dry and "wet" food, from various companies, and occasional scraps from the table. Currently we only feed him dry food from Orijen, and plan on introducing some other "wet" food soon. He's also getting a good quality bones with a lot of bone marrow, and about once a week some boneless sardines in olive oil.
A bit of anecdata - but all of our animals (few dogs, couple cats) have shed significantly less and had a much healthier looking coat once we switched them to better foods.
The reduction in shedding going from kibble that's primarily rice and corn to something that's actually nutritionally appropriate ingredients for a dog/cat was astounding (but should have been unsurprising).
My understanding is that pet allergies are generally allergies to the shed hair and skin, so a healthier diet may have reduced that significantly.
Before my dog was getting a mix of dry and "wet" food, from various companies, and occasional scraps from the table. Currently we only feed him dry food from Orijen, and plan on introducing some other "wet" food soon. He's also getting a good quality bones with a lot of bone marrow, and about once a week some boneless sardines in olive oil.