I believe this site is very good for determining which dog food might be best and how the food you are using is rated. It gives very detailed lists of the good and the bad of the food. It also explains why the questionable ingredients which are highlighted in red are not optimal. I would suggest for a really severe case of itching to try Ziwi Peak Daily Dog which is a dehydrated raw food. It is expensive but it is given a 5 star rating and it is grain free. The site also has a lot of good information and a place where you can sign up to receive recalls.
http://www.dogfoodadvisor.com/Since it isn't always food that causes allergies I found this information on cleaning products. I also try to watch when we are walking that I don't let the dogs walk where they have used lawn sprays, there is usually a little flag like sign.
http://www.allergydogcentral.com/2011/0 ... -products/"As you clean you home to eliminate dust and other allergens, you could be causing more harm than good. Perfumes and chemicals found in air fresheners and cleaning products can often trigger allergic reactions in sensitive dogs.
Many cleaning products today, like dust cleaners, and bathroom and kitchen cleaners, come in aerosol cans or sprays which make it easier to cover large surfaces. Unfortunately, these sprays are also good at sending chemicals into the air, which can then be inhaled by you and your pets.
Laundry detergents and dryer sheets also contain dyes and perfumes which can harm allergy-prone dogs. These chemicals can be particularly bothersome if you wash your dog’s bedding – since your pup will be lying directly on these allergen-rich fabrics."
If your dog is itchy year round, particularly after a house cleaning session, you may want to consider changing your cleaning products to those which are more allergy-friendly.