The Paw Print Genetics Blog

Why is my dog so itchy? Part I: Food Allergies

Why is my dog so itchy? Part I: Food Allergies

The summer season is upon us! Unfortunately, for many dogs, this also means the itchy season. In 2013, according to the veterinary health insurance company, Veterinary Pet Insurance (VPI), trips to the veterinarian for skin allergies were the most frequently submitted claims. In addition, the second highest number of claims came from owners whose dogs had ear infections. Interestingly, one of the most common causes of ear infections in dogs is also allergies.

In my experience, there are many misunderstandings among dog owners when it comes to canine allergic disease. One of the most common misunderstandings I encountered in practice was to blame food first as a cause of their dog’s bad skin. It was not uncommon for an owner of an allergic dog to inform me that they had already changed their dog’s food multiple times, but that it either didn’t help or only helped for a short period of time. Not only can rapid food changes cause severe gastrointestinal issues in dogs, approximately 90% of the time owners are wrong in blaming food, as only 10% of all canine skin allergies are believed to be food related.

Grain-based foods tend to get an unfair portion of blame. Though wheat is indeed one of the top five food allergens in dogs, the other four are beef (the most common allergen of dogs), dairy products, eggs and chicken meat. On the other side of placing blame for their dog’s allergies, I’ve dealt with many owners that believed there was no way for their dog to have food allergies because they were eating a high-quality, expensive, grain-free commercial diet. However, like people, dogs can be allergic to any individual ingredient in their food, including any particular protein source.

Proving Food Allergies

So, your dog has non-seasonal itchiness with occasional or chronic skin and ear infections. You believe that your dog has a food allergy. How do you prove it? By far the most effective way to diagnose a food allergy in your dog is through a hypoallergenic dietary food trial. This is most commonly achieved through the use of three main types of food sources: a hydrolyzed protein diet, a novel protein diet or a home-cooked diet. In some food allergy cases, any of the three would be effective, but in other cases, only one (or none) of the diets may be effective in obtaining resolution.

A hydrolyzed protein diet is one in which the proteins have been processed and broken down into short chains of amino acids that are less likely to be recognized by the body as an allergen. A limited ingredient novel protein diet is one in which you introduce a protein source that the dog has never eaten before (such as kangaroo or rabbit meat) with a single carbohydrate source to further limit potential allergens. Both hydrolyzed protein and novel protein diets should be prescribed and purchased from a veterinarian because, at this point, there are no commercially available, over-the-counter diets that are considered truly hypoallergenic. These diets must be prepared in factories that either don’t produce other types of pet food or have extensive cleaning of machinery between batches of food to prevent allergens from getting into the hypoallergenic food bag. Lastly, home-cooked meals can play a role in hypoallergenic food trials. However, they are not often a first choice for trials because they can take significant time to prepare, can be costly and, without consultation from a nutritionist, are often deficient in many vitamins and minerals. Sometimes however, a home-cooked diet is the only diet available to prevent a food-allergic dog from having issues.

Eliminating Variables

The food selection is only half of the hypoallergenic dietary trial, however. The other half is owner discipline and compliance. The vast majority of the hypoallergenic food trials I prescribed in practice failed due to an inability (or unwillingness) by owners to follow my directions. It is crucial that these dogs be fed a SINGLE food source for 8-12 weeks without any other food, treat, flavored medication or toothpaste. If the dog improves, proof of food allergy can be obtained by placing the dog back on their old food and watching for skin issues. However, I never had an owner willing to try the old food again when the new food fixed their dog’s problems.

In addition to food and owner compliance, it is very important that the dietary trial begins without other complications, such as secondary bacterial skin infections or ongoing inflammation in the skin. Therefore, it is common practice to place these dogs on antibiotics and/or anti-inflammatory medications at the beginning of the trial to limit the variables. In principle, as these therapies are discontinued, a food allergic dog should not become itchy again as long it is still eating the new hypoallergenic diet.

Unfortunately, allergens and the dogs they drive crazy don’t live in a vacuum. In many circumstances dogs have allergies to multiple allergens including “environmental allergens” that further complicate the process of diagnosis and prevention. In upcoming blogs of this series on itchy dogs, we will examine more common causes of itchiness in our canine friends than what is in their food bowl and discuss a severe form of allergic skin disease known as canine atopic dermatitis. 

This column is not intended as a replacement for personalized veterinary care. Please consult your veterinarian for medical advice regarding your pets.



  •          Gaschen FP, Merchange SR. Adverse food reaction in dogs and cats. Vet Clin North Am Small Anim Pract. 2011 Mar;41(2):361-79. doi: 10.1016/j.cvsm.2011.02.005. [PMID:21486641]
  •          Verlinden A , Hesta M, Millet S, Janssens GP. Food Allergy in Dogs and Cats: A Review. Crit Rev Food Sci Nutr. 2006;46(3):259-73. [PMID:16527756]

*Photo courtesy of Mikhail Koninin via Flickr Creative Commons License*