Itching in Dogs: Food Allergies
Food allergies in dogs are rather uncommon, but extremely hard to diagnose. We review symptoms and ways vets diagnose food issues (elimination diets).
In our previous articles about itching, biting, chewing, and scratching in dogs, we reviewed two of the most common causes for these symptoms: seasonal allergies and flea allergic dermatitis. Another culprit that can cause these symptoms in pets is food. Food allergy dermatitis is not as common as the aforementioned allergies, but it does happen and can be frustrating to diagnose and treat.
What Are Some Symptoms of Food Allergies?
An adverse food reaction occurs when there is an abnormal response to the ingestion of certain foods. This response can either be a food intolerance or a food allergy.
Food intolerance occurs when there is a non-immunological response that includes food poisoning from toxic substances, such as chocolate and onions, or the ingestion of garbage. Symptoms can vary depending on the toxin ingested, but often include vomiting and diarrhea.
A food allergy occurs when there is an immune response or hypersensitivity to a food, typically causing digestive or dermatological signs. Food allergy symptoms are gastrointestinal (diarrhea and vomiting) or dermal (lesions on the skin) in nature.
Lesions that pop up on the skin are hives or in veterinary terms, urticaria. These hives are red, raised, and usually round bumps that may pop up within 24 hours of ingesting the offending food. However, in some cases, the lesions develop more gradually and can be the underlying cause of chronic ear infections (otitis externa), skin infections (pyoderma), or paw/nailbed infections (pododermatitis). Most food allergies cause itching, and the patient will commonly paw at their face, neck, or ears. Other pets will chew at their paws or scoot on their bottom due to the irritation.
Diagnosis of Food Allergies
Diagnosis of food allergies is complicated and can be frustrating for both the pet owner and veterinarian. This is because there are no reliable tests currently available to make a definitive diagnosis. Blood, saliva, and hair sample tests have not been proven to be useful. The only way to diagnosis a food allergy is by ruling out the other causes of dermatitis and then going through an elimination diet trial with your pet.
Before embarking on an elimination trial, it is important to note that food allergies account for only approximately 10% of all diagnosed allergies (petfoodinstute.org). In other words, 90% of the time, there is another cause for the itching and scratching, with the most common being flea allergies followed by seasonal allergies. It is important to talk with your veterinarian about the signs and symptoms you are seeing before embarking on the diet trial. I use the term “embarking,” because this can be a long and labor-intensive journey that could last from 6 weeks to several months, depending on your pet’s response or lack of response.
An elimination diet might be the next best step for your pet, but you should rule out all other causes first with the help of your veterinarian. If this due diligence is not done, you might be barking up the wrong tree and this difficult journey could be a waste of time for you and your pet.
An elimination diet is a 6-to-12-week period where only a hypoallergenic diet is fed. That means nothing else, including treats (unless they are the made of the same hypoallergenic formula). Hypoallergenic diets fall into two categories: either a novel protein diet or a hydrolyzed protein.
Novel protein diets typically have a protein source that has not been ingested by the affected pet before and very few additional ingredients. They can be home cooked diets or prescription diets. The idea is that if your pet has never been exposed to the main protein before, they will not react because their immune system has not developed a sensitivity to that protein.
The other type used in trials, hydrolyzed protein diets, reduce the size of the protein, theoretically making it less likely for the body to have an allergic reaction.
Talk with your veterinarian about which elimination diet is best for your pet’s diet trial. Typically, the recommended trial diet will be prescription. Over-the-counter diets are not recommended, because their labeling may not be as accurate, and they were not developed for the gold standard elimination diet trials. If prescription diets are not for you, there are veterinary nutritionists available for consultation (vetmed.ucdavis.edu) who can help formulate a home-cooked trial diet for your pet. But you still need to be just as strict.
In order to truly see if a pet is food allergic, they can only receive the hypoallergenic diet during the trial period. If the food allergy has caused gastrointestinal symptoms, these will usually resolve in 2 weeks. For skin lesions, it can take between 8-13 weeks before improvement is seen. The challenge of an elimination diet trial is keeping your pet away from other foods (and resisting the urge to give them treats).
Dogs are very good at finding food in the home, or at parks and on walks. They’re capable of getting into the trash, sneaking food off the table, and finding scraps of dropped food. Make sure your entire family is on board with the trial, and that they understand that sneaking a treat means you will have to restart the trial.
If treats are desired, one can use any of the ingredients that are found in the elimination diet. Often, these are canned and dry versions of the hypoallergenic foods, making it easy to give treats during the trial. Some of the prescription diet companies also make treats to go along with the primary meal.
Food Allergies Are Complicated
Food allergies are very challenging to diagnosis in pets, and just because a pet responds to the diet trial doesn’t mean that they are food allergic. Veterinarians are often treating the secondary skin problems at the start of the trial, so these patients tend to improve initially, and then relapse when medications are discontinued.
To complicate things even more, if they do not respond to the trial, it doesn’t mean that they are not food allergic. If you can believe it, you can get cross reactivity between proteins. For instance, chicken can cross react with fish, making choosing the novel diet difficult!
There are many causes for the itching, chewing, biting, and scratching, making diagnosing the cause extremely difficult. Fortunately, food allergies are lower on the differential list. If your pet is continuously experiencing any of these symptoms, it is best to talk with your veterinarian about the possible causes, so that you can work with them to create a diagnostic plan. That way, you get to the bottom of your pet’s itching issues in the most efficient way and help them to feel better, faster.
Also, it's always best to be prepared for vet visits related to food allergies. AKC Pet Insurance plans (underwritten by Independence American Insurance Company) offer coverage for allergies and many other common canine emergencies. Click here to create a custom plan fit for your dog and budget.
Dr. Preston Turano graduated from the University of Illinois College of Veterinary Medicine in 2002. Since that time, he has been a Veterinarian, Medical Director, and Practice Owner.READ MORE ARTICLES