Agree - most food allergies are to the protein source, not the grains. There are I'm sure a few dogs that are allergic to wheat, gluten etc. but not very many. To do a proper food trial for food allergies (which tend to persist all year, and can happen at any time even if the dog has been on the same food for years) - minimum 2 months of a hypoallergenic prescription food (or even home cooked - 1 protein source, 1 carb source) with no treats, people food, nothing not even flavored heartworm preventative (like Heartgard, Trifexis, Sentinel, etc. - you have to use Advantage Multi which goes on their back), and a resolution of the itching, along with a re-challenge of the old food at the end, if the itching comes back, it was food allergies.
I am amazed at the number of people buying into the grain free craze...when there is nothing really to back it. Why is corn evil? Obviously it shouldn't be the #1 ingredient but dogs are omnivores...it's okay for them to eat vegetables. Unless your dog is a performance dog (i.e. hunting, field trial, agility, etc) or a puppy, they likely do not need such high levels of protein. Also, there is no reliable skin/saliva/blood test for food allergies.
Dogs also develop seasonal allergies, same as people, however these manifest as skin itching, licking paws/groin/armpits, etc. not hay fever like symptoms. Seasonal allergies is called atopic dermatitis, or atopy. These dogs are itchy for seasons, mostly spring/summer and it occurs yearly, then goes away. Some lucky dogs get both atopy and food allergies. Allergy testing (same as in people) is an option for these dogs.
It really is best to talk to your veterinarian about the signs your dog is having. Skin infections need treatment as they are itchy by themselves, and some dogs need some Pred every now and then to stymy the itch. The point of food trials and allergy testing/shots is to avoid long term use of steroids.
Sorry so long, but allergies are a complicated disease process and there is never a cure, always management. I spend probably 1-2 hours a day talking to clients about allergies (probably more actually since we see a ton of Bulldogs) and it is a difficult topic to get clients to wrap their head around. Everybody wants a quick fix, a cure-all shot, and it doesn't exist.