This is not veterinary advice. It has been sourced from the Internet.

A food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions.

A protein in the food is the most common allergic component. These kinds of allergies occur when the body's immune system mistakenly identifies a protein as harmful. Some proteins or fragments of proteins are resistant to digestion and those that are not broken down in the digestive process are tagged by the Immunoglobulin E (IgE). These tags fool the immune system into thinking that the protein is harmful. The immune system, thinking the organism (the individual) is under attack, triggers an allergic reaction. These reactions can range from mild to severe. Allergic responses include dermatitis, gastrointestinal and respiratory distress, including such life-threatening anaphylactic responses as biphasic anaphylaxis and vasodilation; these require immediate emergency intervention.

Certain breeds of dog are especially prone to allergies, for example:

• Maltese
• Pekingese
• German Shepherd
• Bull Terriers
• Bichon Frise
• English Cocker Spaniel
• Brussels Griffon
• American Hairless Terrier
• Bohemian Terrier
• Shih Tzu
• Lhasa Apso
• American Pit Bull Terrier
• Wire-Haired Fox Terrier
• Chinese Crested/Powderpuff
• Poodle
• Irish Setter
• English Bulldog
• Pug
• Dalmation
• Retrievers
• Miniature Schnauzer
• West Highland Terriers
• American Bulldogs
• 2nd Generation Cross Labradoodles

But there are many more. Many cats also have allergy issues.

Traditional vet thinking treats the symptoms via prednisone pills or shots or a 'super premium dry food' that still contains beef, chicken or wheat. Usually these allergies are in response to beef, chicken or vegetable-based proteins- grain and grain free. 

Another way to treat allergies is by using a novel protein. This is a protein that the body has not encountered previously. Usually this could be rabbit, hare, wallaby, goat, possum or fish.

SOURCE: https://carnivoro.co.nz/pages/allergies-what-are-they