Food intolerance can occur the first time a food is fed. Another aspect of a food allergy is its appearance year-round. Food additives can also trigger an allergic reaction in some pets. Every component of the diet should be suspected. This is why simply changing from one commercial diet to another is seldom successful in controlling food allergies.
Many diets have the same ingredients and preservatives.
Elimination Diet Trial Blood tests and intradermal skin tests may be useful in identifying inhalant or topical allergies, but they are unreliable in recognizing food allergy. Conducting an elimination diet trial is the preferred diagnostic method. An elimination diet is restricted to those foods the pet has previously not encountered. These foods are described as hypoallergic because a pet cannot be allergic to a food if it has never eaten it. There are no foods that are completely nonallergic.