The classical canine food allergy lesion distribution includes signs of facial itching, foot or limb chewing, belly itching, and recurrent ear infections.
In cats, food allergy usually produces scabs and other signs of itching around the face or neck.
(Only some of the captioned signs are usually present in a given animal, not necessarily all.)
Your Pet’s Itchy Skin
Itchy skin in the small animal is often more than just a minor annoyance. Red, oozing bald patches; rashes; and large expanses of hair loss are unfortunate markers of very real discomfort for which a cause should be sought and dealt with.
The food allergy is one of the itchiest conditions known to cats and dogs. Animals eat a variety of processed food proteins, fillers, and colorings that are further processed inside their bodies. Proteins may be combined or changed into substances recognized by the immune system as foreign invaders to be attacked. The resulting inflammation may target the gastrointestinal (GI) tract or other organ systems, but in dogs and cats it is the skin that most often suffers from this immunologic activity.
Many people erroneously assume itching due to food allergy requires a recent diet change of some sort. In fact, the opposite is true.
Food allergy requires time to develop; most animals have been eating the offending food for years with no trouble.
What Kind of Allergy?
Sarcoptic mange and inhalant allergy (also known as atopy) are the two conditions which must be distinguished from food allergy as the treatment approach to each is markedly different. Much time and money can be wasted pursuing the wrong problem.
Please consider the following clues that contribute to pointing us towards the food allergy as a diagnosis. Your pet demonstrates:
Your pet has been treated for sarcoptic mange without any positive change.
Your pet’s itchiness is not and has never been a seasonal problem.
Your pet has responded poorly or only partially to cortisone-type medications.
Your pet has had a skin biopsy demonstrating changes often associated with allergy or, more specifically, food allergy.
A lesion distribution pattern that is common for food allergy (see illustration above).
Your pet did not have skin issues before age 5 or 6.
Any of the above findings or observations warrant pursuit of food allergy.
Note that three of the above four criteria relate to what you, the owner, observe at home. Trouble results when the veterinarian must speak to different family members about the pet and there is disagreement in their observation of the pet at home. It is best to have one person, preferably the one who has the most contact with the pet, be the spokesperson and make the relevant judgments.
The Flea Factor
Some animals have many allergies. It would not be particularly unusual for an animal with a food or inhalant allergy
to also be allergic to flea bites, especially considering that flea bite allergy is extremely common among pets. Because allergies add to each other, it is possible that a food-allergic dog will not itch if its fleas are controlled. Since new technology has made flea control safe and convenient, it is especially important (and no longer difficult) to see that fleas are not complicating a pet’s itching problem.
Ensure immaculate flea control for any itchy pet!
See more information on flea biology and flea control.
How to Deal with the Food Allergy Suspect: The Hypoallergenic Diet Trial
The Basic Principle
To determine whether or not a food allergy or intolerance is causing the skin problem, a hypoallergenic diet is fed for a set period of time. If the pet recovers, the original diet is fed for up to two weeks to see if itching resumes. If we see recovery with the test diet and itch with the original diet, then food allergy is diagnosed and the pet is returned to either the test diet or another appropriate commercial food indefinitely.
What is a Good Hypoallergenic Diet?
There are two approaches to this question. Obviously, the test diet must be of a food source that the patient could not possibly be allergic to. The traditional method is the use of a novel (new to the pet) protein and carbohydrate source; that is, something the pet has never eaten before. In the past, lamb has been the protein source of choice as American pet food companies had traditionally failed to produce lamb-based pet foods. Unfortunately, recent production of lamb and rice-based foods has removed lamb from the acceptable hypoallergenic diet list for most pets.
Fortunately, many pet food companies have discerned the need for diets using unusual protein and carbohydrate sources with a minimum of additives. Foods can be obtained based on venison and potato, fish and potato, egg and rice, duck and pea, and even kangaroo. Diets used for allergy trials must contain basically one protein and one carbohydrate source and neither can be something the pet has had before. Recently several diets that include duck, venison, and so on have been released to the general market. Be aware of foods that contain these ingredients because these ingredients will not be useable for future diet trials if they were ever used in the pet’s regular food.
It is important that no unnecessary medications be given during the diet trial. No edible chew toys (such as rawhides or bones) should be given. Treats must be based on the same food sources as the test diet. (Beware of rice cakes, though, as wheat is commonly used as a filler.) Chewable heartworm preventives should be replaced with tablets.
Home cooking was originally the only option felt to be appropriately free of allergens but for most animals these special commercial foods are adequate. Occasionally home cooking ends up being necessary after all. Recipes for appropriate diets can be purchased through www.balanceit.com, a website set up by the American College of Veterinary Nutrition.
The Hydrolyzed Protein Method
Recently a new approach has been introduced using therapeutic diets made from hydrolyzed proteins. This means that a conventional protein source is used but the protein is broken down into molecules too small to excite the immune system. Some hydrolized diets are on the market; discuss with your veterinarian which is best for your pet.
How Long to Feed the Trial Diet
In the past, four weeks was thought to represent a complete trial period. More recent work has shown that only one food allergic dog in four will respond within this time frame and that a more appropriate trial period would be 10 to 12 weeks. This may be an extremely inconvenient period of time to home cook. Some veterinarians recommend a recheck appointment or a phone call after four weeks of diet trial and then again after 8 weeks. Eighty percent of food-allergic dogs will have responded to diet trial at least partially by six weeks. The Labrador retriever and cocker spaniel appear to require longer trials.
Most commercial diets used in food allergy trials have a 100% guarantee. This means that if your pet doesn’t like the food, the food can be returned for a complete refund, even if the bag is opened. This is especially helpful for feline patients, as cats are famous for being choosy about what they are willing to eat.
What to do if the Diet is Successful?
To confirm food allergy, return to the original food; itching resumes within 14 days generally if food allergy was truly the reason for the itchy skin. Many people do not want to take a chance of returning to itching if the patient is doing well; it is not unreasonable to simply stay with the test diet if the pet remains free of symptoms. Often it is difficult to remember 10 to 12 weeks later how itchy the dog used to be before the diet trial. The diet challenge helps make it more obvious whether the diet trial has worked or not.
It is possible to more specifically determine the identity of the offending foods after the pet is well. To do this, a pure protein source (such as cooked chicken, tofu, wheat flour or any other single food) is added to the test diet with each feeding. If the pet begins to itch within 2 weeks, then that protein source represents one of the pet’s allergens. Return to the test diet until the itching stops and try another pure protein source. If no itching results after two weeks of feeding a test protein, the pet is not allergic to this protein.
What to do if the Diet is Unsuccessful?
Assuming secondary skin infections have been controlled, an unsuccessful food trial is strongly suggestive that an inhalant allergy is the primary problem but there are some other considerations that should at least be mentioned:
Are you certain that the dog received no other food or substances orally during the trial?
Was sarcoptic mange ruled out?
Your pet may require a longer diet trial. Are you certain regarding the factor which pointed toward the food allergy?
If your pet has not been biopsied, now may be a good time. If an inhalant allergy has risen to the top of the list, symptomatic relief either via medication, baths with specific shampoos, or allergy shots will likely be necessary. Chronic itchiness can be extremely uncomfortable and prompt relief is our goal as well as yours.
Information on itch relief.
Information on airborne allergies.
Information on sarcoptic mange.
See a veterinary nutritionist’s thoughts on Food Allergy Trials in Dogs.
For treats appropriate to dogs on a food trial see:
www.snookdog.com for sweet potato treats;
www.sitstay.com for rabbit ear treats, venison sausage, carrot dental bones, turkey jerky strips, rabbit ear treats, Icelandic fish chews, and other novel protein-based treats.
Other acceptable products include those made of pig parts: ears, snouts etc.
Date Published: 1/1/2001
Date Reviewed/Revised: 04/11/2011