Just as people can be allergic to certain foods, so can pets. A food allergy in a dog or cat results most typically from a protein in the food. Food allergies most commonly cause skin issues in dogs and cats, but vomiting and diarrhea can occur, too. Treatment involves removing the offending ingredient from the pet’s diet. Finding the offender usually involves a process of elimination.


Food allergy (also called food hypersensitivity) refers to a type of physical reaction to food.

Food reactions are classified into two categories: those that are the result of immune system stimulation and those that are not. Food allergy occurs when the immune system begins to overreact to ingredients that the pet has eaten with no problems in the past. Food intolerance occurs when what is eaten has a direct, negative effect on the stomach and/or intestines, such as spoiled meat, chewed-up toys, food additives, and abrupt changes in diet. Food intolerance is not an immune disorder and, as such, will not be treated here.

The list of known food allergens (substances that pets can be allergic to) is extensive and includes beef, eggs, poultry, dairy, lamb, pork, fish, corn, wheat, soybeans, preservatives, and dyes. Typically, it is the protein source in a pet’s diet that elicits an allergic reaction.

Overall, the immune system’s job is to find threats to the body and destroy them by sending signals to activate special cells. An allergy results when this system misjudges a safe substance and the cells damage the surrounding tissues. This is why animals with food allergies can sometimes experience vomiting and diarrhea. Food allergies in pets, however, will most commonly cause problems in the skin.

Symptoms and Identification

Skin signs include:

  • Itchiness (all over or even in just a few areas)
  • Skin infections
  • Ear infections
  • Hair loss

Stomach and intestinal signs include:

  • Vomiting
  • Diarrhea
  • Abdominal pain
  • Weight loss

Many diseases can cause either gastrointestinal signs or itchiness, so the diagnostic approach undertaken by veterinarians includes ruling these out as part of the diagnosis of a food allergy. Food allergies tend not to be seasonal, and signs are usually seen year-round. The most obvious indicator of a food allergy is that the signs clear up when the responsible ingredient is removed from the diet.

A so-called “elimination diet” is the only proven way to determine which food is affecting a pet. Elimination diets consist of ingredients that haven’t been offered to the pet in the past. We call these “novel” ingredients. Many commercial therapeutic diets are available to offer hard-to-find protein sources.

The elimination diet can be thought of as a diagnostic test that may last up to 12 weeks. This test takes so long because the allergen may continue to stimulate your pet’s immune system for weeks after it is eliminated from the diet. The elimination diet will be the only food that a pet is allowed to eat during the trial period. During this time, no other food or treats may be fed unless they are restricted to the same “novel” ingredients in the elimination diet. Rawhide (usually made of cowhide), pig’s ears, and any other chew items or toys should also be avoided if they contain other ingredients. Even regular medications, such as heartworm preventives, must be given in a non-flavored form to keep the pet from being stimulated anew by the ingredients in these preparations.

Veterinarians will typically treat food allergic pets for secondary skin infections or any gastrointestinal symptoms at the beginning of the diet trial. These problems will often fail to resolve without specific medication aimed at these symptoms.

If the skin and gastrointestinal problems resolve during the trial, a veterinarian may then “challenge” a pet’s immune system by feeding the previous diet to see if the signs come back or by systematically adding specific items back into the diet. The diet used for the elimination trial may be fed after the trial is over. That is, if it is balanced and formulated to provide complete nutrition.

It bears mentioning that blood tests for food allergies are widely available and may be helpful in helping guide the choice of an elimination diet. Unfortunately, recent thinking in dermatology circles suggests these tests are too nonspecific and insensitive to replace the elimination diet as the gold standard test for food allergies in pets.

Affected Breeds

No breed predilection for food allergies has been firmly established in cats or dogs.


This is one of those conditions for which the diagnostic process may yield the ideal treatment plan. Arriving at the correct diet may seem like a frustrating game of trial and error, but it will often bear fruit treatment wise, too.

This article has been reviewed by a Veterinarian.