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Food Allergies in Pets: Signs, Common Triggers, Diagnosis & Treatment | VetDERM Clinic

Food Allergies in Pets: Signs, Common Triggers, Diagnosis & Treatment


What is a Food Allergy?

Food allergy constitutes an overreaction of the immune system to a particular ingredient in the diet, usually a protein molecule. This over-reaction can cause a variety of symptoms that are associated with inflammation in the body. The clinical signs that we associate with a food allergy are a result of the inflammation of skin, intestines, eyes and/or the respiratory system. Dogs and cats may show one or more of these symptoms. Each individual is different and signs related to the same problem in 2 different pets may be similar or quite different from each other. Similarly, pets affected by different allergies can show the same set of allergy symptoms. Common signs of food allergy in pets are listed below:

What are the signs of food allergies in pets?

  • Itching; including licking, scratching, biting and rubbing of the skin of face, paws, back, limbs, bum and ears
  • Redness of skin and ears 
  • Dryness of skin
  • Increased dandruff
  • Oily skin and hair coat
  • Repeated ear infection and inflammation
  • Repeated skin infection
  • Over-grooming (excessive grooming) in cats
  • Any self grooming in dogs 
  • Hot spots (eczema) of skin
  • Hair loss
  • Gastrointestinal problems such as soft stool, diarrhea, vomiting and gas 
  • Increased frequency of bowel movements
  • Watery eyes or other eye discharge
  • Redness of eyes
  • Sneezing and/or reverse sneezing 
  • Swelling of eyes or face

Most of the signs associated with food allergy are also signs associated with other more common allergies, including environmental allergy and flea bite allergy. Thus, the suspicion of food allergy should also be accompanied by other allergies, until the pet is comfortable and the cause determined accurately. 


Only about 10-20% of all allergy cases in dogs and cats are due to food allergy. Despite food allergy not being very common in pets, food changes and evaluation of food allergy is often recommended. If a food change is recommended, it is not a diagnosis, rather a test to assess for food allergy. Knowing this and performing a good food work up can help prevent frustration and confusion as a pet parent. The information below should help understand the “why” and “how” of food changes, and help prevent an unending series of food changes for your pet.


Some pets may be affected by a combination of food allergy with other allergies. Thus, diagnosis of a food allergy does not rule out other possibilities.


How to diagnose and treat a food allergy?

If your veterinarian suspects your dog or cat has a food allergy, diagnosis is usually done with a dietary elimination food trial using a specific type of food for a period of time, usually 2-3 months long.


The elimination food trial is a diagnostic test, and should always be performed under the supervision of a veterinarian or vet dermatologist. It is not simply a change of food, or a series of food changes. Sometimes additional treatments may be needed for a reliable and informative food trial. 


Also, the correct diet change, specific to the pet’s needs should be made. This may be based on your pet’s age, general health status, previous diet and symptoms being exhibited. A diet that worked for a friend’s pet or for your own previous pet may or may not be the right choice for other pets. 

When an appropriate diet trial is initiated, it can be quite reliable, if strict dietary control is adhered to. Your veterinarian may advise on a food that is composed of a hydrolyzed protein. This is a protein that is broken up into such small molecules that the immune system is unlikely to recognize it as a “problem ingredient”. This is similar to hydrolyzed milk products made for lactose intolerant humans. Alternatively, an elimination food trial using a single novel protein source may be advised. This is a food composed of the single new protein and other ingredients your pet has not been exposed previously, thus making a reaction to these ingredients unlikely.


Your veterinarian or vet dermatologist will need to review your pet’s medical history in detail with you, before determining the correct diet for your pet’s food trial. There is no diet that can be ‘blindly’ prescribed for all pets suspected of a food allergy.


Home-made diets prepared by the pet owner (with the help and guidance of a veterinarian, veterinary dermatologist and/or veterinary nutritionist) can also be used for dietary trials if there is a personal preference to pursue this option, or for pets that have been sensitive to commercial diets. It is important to ensure good allergy work up decisions, while keeping in mind the pet’s whole body nutrition when deciding on such home-made diet trials. 

In order for food trials to be effective, they have to be kept very strict. Even the smallest piece of potential allergen can cause allergy symptoms after ingesting them! It’s important your pet stays on the appropriate diet for a minimum of 2-3 months. That means no treats outside of the recommended diet regimen! Some treats may be approved by your veterinarian, depending on the ingredients of the primary diet selected, if deemed appropriate. 


Remember, the 2-3 month long dietary control is a diagnostic test. Also, you may recall from the above information, food allergies are not very common even in allergic pets. After completion the food trial, we will want to learn if your pet is even has food allergy, or is affected by other allergies that mimic signs of food allergy. This is done using the oral food challenge, which is usually 7 days long in cats and 14 days long in dogs. 


Once the food elimination trial is completed, our dermatology team recommends a dietary re-challenge, to help prove or rule out a food allergy affecting the pet. The above process is also best undertaken under the supervision of a a pet dermatologist or a veterinarian comfortable with this part of the food allergy diagnostic process. 

Once a controlled diet work up is done and if food allergy is diagnosed for your pet, treatment is simple. The ‘treatment’ of a food allergy is simply avoidance of the food allergens affecting your pet! Alternatively, you may simply continue the diet that has been approved by your vet and is working in providing comfort for your pet, while avoiding other ingredients that have not been assessed using a diet challenge. 

Food Allergy Triggers in Pets

Most commonly, dietary triggers are proteins. This makes meat sources and dairy common allergens in both cats and dogs. However, some carbohydrate sources as well as vegetables and fruits may be allergens in specific individual pets. Once an allergic pet is exposed to their allergy trigger food, they may take a few days to exhibit allergy symptoms, or may react within hours of ingesting the allergen.

Some Common Allergy Triggers in Dogs

  • Beef
  • Chicken
  • Dairy
  • Lamb
  • Egg
  • Pork
  • Wheat
  • Rice 
  • Soy

Some Common Allergy Triggers in Cats

  • Fish 
  • Beef
  • Chicken
  • Dairy
  • Lamb
  • Egg
  • Wheat

While the sources listed above are common triggers, an allergy can develop against any protein source in the food. Food allergies can also develop at any time in your pet’s lifespan. Some pets may have been eating the diet for years before becoming allergic to it. It cannot be assumed that a diet fed long term to a pet is not the cause of the allergy, if they are demonstrating sudden allergy symptoms. 

The process of assessing for a food allergy can take some time and patience, but once you find what works for your pet, they will thank you for a more comfortable life! With the guidance of your vet dermatology team, we can help make this diagnostic and transitional period as effortless as possible for you and your four-legged companion!

Creative Commons Attribution: Permission is granted to repost this article in its entirety with credit to VetDERM Clinic and a clickable link back to this page.


Dr. Jangi Bajwa


Dr. Jangi Bajwa is a Board certified veterinary dermatologist at VetDERM Clinic in Surrey BC. He is also the dermatology feature editor for Canadian Veterinary Journal. Dr. Bajwa’s special interests include otitis and allergic disease in pets; as well as helping improve quality of life of pets and their families.


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