Does Your Pet Have a Food Allergy?

Last Updated SUN 27 OCT 2019

This article is written by Pet Circle veterinarian, Dr Kim Chainey BVSc.

Are you suspicious that your pet may have a food allergy? Food allergies are responsible for approximately 10% of allergy cases in dogs, ranked third after flea allergy and atopic dermatitis (airborne allergies) - although food allergies are a little more common in cats.

Strictly speaking, we should call food allergies an adverse food reaction because it occurs when the immune system reacts to a particular pet food ingredient. The incriminating component of the food is usually the protein source - for example chicken, beef, soy, or dairy. These proteins usually resist the heat of cooking, stomach acids, and intestinal digestive enzymes, and make their way to the bloodstream and target organs where they can cause an allergic reaction. Most pets that develop food allergies, do so over a period of months or years of being exposed to a particular food.

Signs of a Food Allergy

  • Pruritus - severe itching of the skin. The itching can affect any part of the body but typically we see scratching of the tummy, armpit, groin, muzzle, around the eyes and the webbing between the toes.
  • Approximately 50% of dogs have gastrointestinal signs such as vomiting, diarrhoea, flatulence and colitis
  • 50 - 80% of dogs develop recurrent ear infections

Pets with adverse food reactions will display these signs all year round, unlike other causes of itchy skin such as environmental allergens which may flare up during spring.

Pets of any age can develop adverse food reactions however, it's more common in puppies and young adults and we usually see signs before 3 years of age.

How are Food Allergies Diagnosed?

If your pet has itchy skin due to allergies, it can be difficult to determine the underlying cause. As flea allergy dermatitis is the most common cause of itchiness in dogs and cats, you should make sure that your pet's flea prevention is up to date with a monthly flea preventative product such as Nexgard or Bravecto.

Our Top Recommended Flea Products

If your pet is still itchy and fleas are no longer part of the equation, your best bet is to consult your veterinarian for further advice. They may recommend a dietary trial. See below for more about this.

What is a Dietary Trial?

A 'dietary trial' or an 'elimination diet' is used as part of the diagnostic process to pinpoint which allergen your pet is allergic to.

The 3 Options For A Dietary Trial

  • A novel ("new") diet
  • A hydrolysed diet - these are prescription/veterinary diets which can only be recommended by your veterinarian
  • Home-cooked diet

The chosen diet must be fed exclusively for a minimum of 6 weeks, with absolutely no treats or tidbits as this may affect results. All other flavoured tablets (e.g. heartworm prophylaxis), flavoured antibiotics and vitamins, toothpastes, pigs ears and rawhides must be excluded. (Every family member should be aware of how important this is!)

If the symptoms improve after 4-6 weeks on the dietary trial, you can assume a food reaction was responsible for your pet's symptoms. You can then introduce one ingredient per week (for example, try chicken the first week, then beef the next week, etc) and observe for a reaction. This allows you to pinpoint what your pet may be allergic to.

In reality, if the symptoms have resolved with the new diet, it may be fed long-term.

So which diet do we choose? While there are advantages and disadvantages to each, the most important factors to initially consider are: What am I currently feeding and what is the protein source? And what other treats or table scraps am I feeding? This will then allow selection of a truly novel protein source.

1. A Novel Protein Diet

What is it? A diet containing a new protein source that hasn't been fed before, such as venison, rabbit, or seafood.

Pros: Commercially available, highly palatable, easy to use, affordable

Cons: Choices have become more limited due to expansion of pet food industry; protein sources that were once "unusual" are now more common

Examples: Hill's Prescription Diet d/d, Ivory Coat Ocean Fish, Taste Of The Wild Pacific Stream, Canidae Pure Sea, Earthborn Holistic Coastal Catch, K9 Natural Lamb Feast

2. A Hydrolysed Diet

What is it? A diet in which the protein source is broken down into smaller molecules that are less likely to trigger an allergic response.

Pros Commercially available - however must be prescribed by a veterinarian. Avoids pet food additives that might have the potential to cause an adverse reaction.

Cons: More expensive, reduced palatability, and a lack of evidence documenting whether dogs allergic to the parent protein will actually tolerate a hydrolysed product.

Examples: Hill's Prescription Z/d, Royal Canin Hypoallergenic, Royal Canin Anallergenic, Royal Canin Sensitivity Control

3. Home-Cooked Diet

What Is it? A diet prepared at home with a novel protein and carbohydrate source.

Pros: Can be prepared affordably depending on the recipe.

Cons: Contraindicated in growing animals due to risk of skeletal and organ pathology if incorrectly formulated or balanced, not recommended in cats, not recommended for long-term feeding

Examples: Usually consists of 1 protein and 1 carbohydrate source e.g. Salmon and potatoes. For a balanced recipe, we recommend consulting with a veterinary nutritionist.

Hypoallergenic Diets

If your veterinarian has recommended a prescription or veterinary hydrolysed diet, it's likely that they've recommended one of the following varieities. But what's the difference? Royal Canin Hypoallergenic versus Anallergenic? Hill's Z/d versus Hill's D/d? See the following table which highlights the characteristics of each:

Name of Food Type Prescription required? Suitable for... First 5 Ingredients How does it help the skin?

Royal Canin Anallergenic

Hydrolysed diet


Elimination diet trials / Severe food allergies

Maize starch, feather hydrolysate with low molecular weight, copra oil, soya oil, minerals

The hydrolysed formula prevents any reaction in dogs where food allergy is the primary cause

Royal Canin Hypoallergenic

Hydrolysed diet


Elimination diet trials / Severe food allergies

Rice, hydrolysed soya protein, animal fats, minerals, hydrolysed poultry liver

The hydrolysed formula prevents any reaction in dogs where food allergy is the primary cause

Hill's Prescription Diet Z/D

Hydrolysed diet


Elimination diet trials / Severe food allergies

Corn Starch, Hydrolyzed Chicken Liver, Soybean Oil, Powdered Cellulose, Calcium Carbonate

The hydrolysed formula prevents any reaction in dogs where food allergy is the primary cause

Royal Canin Skin Support

Skin Care Diet (Prescription)


Moderate-Severe Sensitive Skin - Dry Skin, Contact or Seasonal Allergies

Rice, dehydrated poultry meat, animal fats, vegetable fibres, hydrolysed animal proteins

Skin barrier support with added aloe vera, beneficial oils, marigold extract, antioxidants (Vitamin E) + omega fatty acids. High quality protein.

Hills Prescription Diet Derm Defense

Skin Care Diet (Prescription)


Moderate-severe Sensitive Skin - Dry Skin, Contact or Seasonal Allergies

Brewers Rice, Chicken Meal, Whole Grain Sorghum, Cracked Pearled Barley, Pea Protein

Skin barrier support with added bioactives and phytonutrients, antioxidants (Vitamin E) + omega fatty acids. High quality protein, free from corn.

Further Reading

How To Get Rid of Fleas in Dogs

Stop the Scratching: Cures for Skin Allergies in Dogs

How to get rid of fleas on your cat once and for all

Know Your Parasites: Fleas, Ticks, and Worms

Complete Guide to Cat Flea and Worming Treatments

Yeast infections in pets