Hi - 90% of allergies (excluding the obvious FLEA allergy!) in dogs are caused by a condition called atopy, which is the immune system overreacting to something in the environment such as pollen, mold, dust mites, cat dander, human dander, etc. The other 10% or so of dogs may have food allergy. Of those dose with food allergy, about 90% will have an allergy to the protein source in their food. That could be chicken, beef, soy, etc. Only 10% of the 10% who have food allergies will be allergic to a grain such as corn, wheat, etc. If you suspect your pet has atopy, the first thing to do is to minimize contact with allergens. Bathe weekly in gentle shampoo, wipe feet when coming in from outside, wash bedding at least weekly, vacuum daily, dust regularly. Your vet can also recommend some medications if necessary. If your pet has food allergies, you will need to feed a prescription diet from your vet along with NO other foods, treats, flavored medications, rawhides, etc. There are some over the counter foods marketed toward food-allergic dogs, but they have all been shown through independent studies to have contamination from ingredients that they are not supposed to contain (i.e. a fish and potato diet might have contamination from chicken) because they are processed in facilities that also process other foods.