[anonymously]

Food sensitivities usually result in GI distress such as vomiting and diarrhea. Food allergies are rare.
It may be time to consider getting the skin testing done by a dermatologist/specialist.

You may find this site informative. http://skeptvet.com/Blog/?s=allergies
And:

Dermatology – Common Issues

“Atopic dermatitis is a hypersensitivity or over-reaction to a variety of commonplace and otherwise harmless substances in the environment such as plant pollens, house dust mites or mold spores. Most pets with atopic dermatitis either inhale or absorb their allergens through their skin. Allergy tests are used to identify what a pet is allergic to in their environment”.

excerpt below from: http://www.2ndchance.info/Apoquel.htm
Food Allergies are probably over-diagnosed in dogs (they account for, perhaps 5-10%). Hypoallergenic diets are occasionally, but not frequently, helpful in canine atopy cases but you should always give them a try. Food intolerances are more common – but considerably more likely to result in digestive disturbances and diarrhea than in itching problems.

Also, via the search engine here: /forums/search/allergies/

BTW: Allergen Specific Immunotherapy does not address food allergies (rare) or food sensitivities.

A common environmental allergen is the household dust mite, also known as Cockroach, American and Tyropagus putrecentiae. And, no, you don’t have to have cockroaches in your home. These microscopic particles are everywhere, airborne and on the skin of all living things…including you! Constantly being shed all year round.

Frequent bathing (Malaseb) might help but it won’t completely solve the problem. Also, allergies tend to get worse as the dog gets older.

Folks will recommend an elimination diet, but how will you know if the dog is responding to environmental allergies, which is causing what? I didn’t find elimination diets helpful.
However, my dog does best on Nutrisca Salmon and Chickpea.