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Allergy Myth

Was it Something I Ate?

One symptom commonly attributed to a food allergy is frequent licking of a specific part of the body, often the paws. Yet several other conditions can prompt this behavior in pets.

Yeast or Bacterial Infection
A yeast or bacterial infection of the skin is a potential cause of itchiness in companion animals that can prompt scratching or licking.

Cats and dogs are affected by several parasites that can cause itching, including fleas with bites that can cause an allergic reaction; mites that look like dandruff, called Cheyletiella; and Sarcoptes scabiei, the mite responsible for canine scabies, better known as mange.

Contact Dermatitis
Pets can come in contact with an array of substances with the capacity to irritate the skin: household cleansers, fertilizers and lawn treatment products, carpet cleaners, deicers and salt. For some pets, even grass and their bedding material can cause skin irritation.

Behavioral Issues
Dogs may lick themselves in response to stressful situations, such as when they experience separation anxiety. Animal behaviorists have found that some dogs even suffer from obsessive compulsive disorder, which could manifest in the form of habitual licking.

Not every cat or dog experiences allergies, just as with people. It is estimated that ten to twenty percent of pets experience some type of allergy depending upon geographic area.

Of those pets that do experience one or more allergy, causes are varied including environmental substances such as dust, dust mites, pollen and molds; flea bites; physical contact with substances in the environment (contact dermatitis); and in some instances, food.

Flea bites are the biggest cause of pet allergies, and environmental substances are often viewed as the second most significant allergen, although climate does impact the prevalence of both. In cooler areas where flea populations may be reduced or nonexistent and the pollen season may be shorter, these two causes may be less significant.

Flea Bites

Flea bite allergy is caused by an allergic reaction to the saliva of the flea. Sensitive animals can experience immediate itchiness, redness and swelling. An animal’s innate response to scratch or bite the affected area can cause hair loss and abrasive injury to the skin that could potentially lead to infection.

"Flea bite is the number one allergy cause, and both environmental allergies and food allergies are relatively rare in comparison,” says Dr. Joy Barbet, clinical assistant professor of veterinary dermatology with the University of Florida College of Veterinary Medicine.

Food Allergies

Food allergies as a group may be next in line in terms of the number of affected animals, again depending upon geography. It is impossible to generalize about specific pet food ingredients as being causative. Because of the great diversity among cats and dogs, what affects one animal may be fine for another. Alternatively, what doesn’t cause an allergic reaction in most pets could cause an allergic reaction in a small number of animals, just as in people.

For those small numbers of animals that do have an allergy to food, it is possible to diagnose the particular ingredient responsible for the allergic reaction.

"Clinical suspicion is not the same as a confirmed diagnosis,” said Dr. Kathryn Michel, associate professor of nutrition at the University of Pennsylvania School of Veterinary Medicine. "Diagnosing a food allergy in a pet requires commitment by the pet owner to follow a strict feeding protocol for a period of at least 8-12 weeks.”

The Protocol

It is impossible to diagnose a food allergy simply by looking at a pet. Diagnosing a food allergy in a pet requires following a specific procedure over the course of 2-3 months.

First the veterinarian prescribes a diet that is free of all protein and carbohydrates sources that were present in the original diet. For a period of 8-12 weeks, the pet owner must feed the exclusion diet and ensure that no other food is given. This prohibition on other food includes the feeding of treats, chews (e.g., rawhide, hooves, ears and pizzles), flavored chew toys, vitamins and supplements, and even flavored medications such as heartworm preventatives. The purpose of this strict regimen is to prevent the pet from consuming any possible item that could cause an allergic reaction.

During this time the pet owner and veterinarian monitor the pet to determine if clinical signs diminish and are eliminated. If clinical signs continue at the end of the 12 weeks, generally a new diet containing different novel protein and carbohydrate sources will be tried. Typically up to three distinct diets will be tested in the event that clinical signs persist throughout the protocol.

If clinical signs do abate, then it is necessary to validate the diagnosis. At this time, the pet is fed the original food to observe if clinical signs return. The onset of clinical signs confirms an allergy to the original diet, but not a specific ingredient.


In the event the symptoms disappear at the end of the 8-12 week period, Dr. Barbet explained that it may be useful to feed the pet single ingredients to identify which one is cause the problem. Then the owner can shop for a commercial diet that does not contain the offending food or foods.

After a diagnosis the pet owner should work with a veterinarian to identify an appropriate diet that is non-allergenic for the pet.

Other Causes

If clinical signs do not abate by the end of the protocol, or if they do not return when the pet is challenged with the original diet, then it is likely that the pet is experiencing something other than a food allergy.


Adapted from "Busting the allergy myth”, PFI Monitor, Spring 2011.

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