Food Allergies

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Food allergies occur in dogs and cats, primarily to a protein in the food. Signs include itchy paws, face, ears, and belly,  skin and ear infections, and may or may not occur with gastrointestinal abnormalities. Food allergies and environmental allergies can look very similar and can occur together, so working with a veterinarian to perform an elimination diet trial using a prescription diet is the only way to diagnose a food allergy, as blood tests for food allergies in dogs at cats are not reliable at this time. Check out images of pets with food allergies and listen to the episode for more information.


Welcome to today’s episode of your vet wants you to know and today we’re going to be talking about food allergies in dogs and cats. Allergies are one of the most common reasons that people bring their pet to the vet, and one of my favorite things to talk about. 

[00:01:19] We talked about flea allergies in episode one and if you haven’t listened to that already, I highly encourage you to go back and listen to the episode about fleas and flea allergies, because this is the most common type of dermatitis that we see in dogs and cats. Flea allergies are diagnosed and based on the appearance of the dog or the cat. Typically with dogs, you’ll see hair loss, redness, crusting, and itchiness around the base of the tail, the rump, and on the inside of the thighs. Cats will have hair loss on their back, their sides, their belly, and their back legs, but you can also see redness and crusting on their skin as well as large red plaques known as eosinophilic granulomas. There’s some really great pictures of these on the website, in the show notes for episode one. While it’s helpful to find either fleas or flea dirt on the animal’s skin, these do not necessarily need to be present in order to diagnose a flea allergy. The diagnosis is made based on the appearance of the dog or cat skin and the lack of an effective flea prevention. The good news is that this is fairly easy to treat by addressing any secondary infection that’s been caused with either a medicated shampoo or an oral antibiotic, some type of itch relief and strict year-round flea prevention for all pets in the household. I hope the only type of allergy your pet has is flea allergies, but if that’s not the case, over the next few episodes, we’ll be taking a deeper look into the other types of allergies, allergy, medications, and secondary complications of allergies. 

[00:02:45] I want to talk about one of my favorite patients, Cookie. Cookie and her owner are very special to me. Cookie’s a young black lab and like most black labs, she has boundless energy. When they came to see me for their first visit, her owner was frustrated because he had been dealing with ear infections for many months. They were so bad that we wound up needing to do a deep ear cleaning and video otoscopy under anesthesia in order to remove all of that gunk that had built up in Cookie’s ears. But it wasn’t just enough for me to deep, clean those ears and address that infection. I talked to Cookie’s owner about needing to get to the root cause of the infections so they didn’t return. We started a diet trial to investigate food allergies and wound up diagnosing Cookie with severe food allergies. Over the course of many months Cookie’s owner and I worked together to do a lot of individual ingredient challenges to figure out exactly which proteins she could safely eat and which proteins would cause her ears to flare up. Now, when Cookie’s owner wants to use a high value treat to channel her energy into agility training, he knows exactly which treats she can have. Cookie’s one of my favorite food allergy patients because of how diligent her owner has been with investigating and managing her food allergies.

Clinical Signs

[00:03:57] So when we talk about the clinical signs of a disease, especially when it comes to allergies, I’ll describe to you what the most common signs are that are written about in textbooks, but I always like to warn pet owners that not all pets read the textbook. So some pets don’t exactly fall into this classic description of clinical signs. Food allergies in dogs typically start as just an itch and the most common places for dogs with food allergies to be itchy are the paws, the belly, the face, the ears, and their armpits. Some dermatologists like to say “ears and rears” for dogs with food allergies, but there are other places the animal can be itchy from food allergies and dogs with environmental allergies can also be itchy on their ears and rears. Cats, in true cat form, itch wherever they want, but it’s not uncommon for me to see beautiful bald bellies in allergic cats, and that’s because itchy cats more often manifest their itch by over grooming rather than scratching and chewing like dogs do. Have you ever felt a cat’s tongue? All those little barbs make the perfect little scratching tool.

Chronic food allergies have led to hair loss, redness, and severe itching on the belly, legs, chest, neck, and face of two different dogs with secondary skin and ear infections.

[00:05:00] It is impossible to tell the difference between an animal with a food allergy and an animal with an environmental allergy based on where they are itchy on their body alone.  To complicate things even further, there are definitely allergic animals out there that can have both a food allergy and an environmental allergy. There are some things that can be helpful in making me more or less suspicious of food allergies versus environmental allergies, and that’s things like the age of onset, whether or not the animal also has gastrointestinal issues and whether or not the itch is seasonal or non seasonal.

[00:05:33] Most pets with food allergies, they’ll start to develop signs when they’re very young, often before they’re a year old, however food allergies can actually develop at any age, even in pets that have been fed the same food their entire life or pets that have been fed lots of different foods over the course of their life. So, if I have an older pet that comes to me for allergies that’s never been itchy before in it’s life, once I make sure that that itch is not coming from infection, I’m going to strongly recommend an elimination diet trial to investigate underlying food allergies. We’ll talk more about diet trials in just a moment.

[00:06:09] Gastrointestinal signs are also a strong indicator of an underlying food allergy. This can be things like soft stool, diarrhea, farts that can clear an entire room or an increased frequency of poops. Most animals should poop once or twice a day. It is not normal for your animal to have four to six poops in a 24 hour period, you are going to run out of poop bags. Not all dogs with food allergies will have gastrointestinal signs. So just because they have normal poops doesn’t mean that food allergies are not a possibility. Food allergies are generally non-seasonal since the food is usually the same throughout the course of the year. Environmental allergies can also be non seasonal. So if an allergy is present year round, it can either be due to food allergies or environmental allergies or both. 

severely swollen paw with interdigital furuncle/cyst and draining tract in a dog with allergies

Itchy paws can develop redness and swelling between toes and salivary (brown) staining from licking.

[00:06:58] While food allergies start as just an itch, it almost always develops into secondary bacterial or yeast infections in either the skin or the ears or both. That’s usually when a lot of pet owners really start to notice that something’s up. They’ll keep bringing the pet back to the vet for an infection which will improve while it’s being treated, but then once the treatment stops that infection comes back very, very quickly. This is the key point that I want to emphasize. Skin infections and ear infections are a secondary problem in animals with allergies. The reason that secondary skin infections and ear infections occur is because the primary disease is not being addressed, and that primary disease is the allergy.  While we have lots of tools for managing allergies, unfortunately, allergies are very rarely cured. If a pet owner stops providing treatment for the allergy, the itch will return and the infections will follow. That’s why it’s so important, when I discuss ear infections and skin infections with pet owners, that I also emphasize that the primary disease must be managed, otherwise they’ll continue to get frustrated that the infections keep coming back. Fortunately, Cookie’s owner understood this and since we’ve managed the food allergies, her ear infections have not come back.

[00:08:13] Most food allergies are to a protein that’s in the diet and the most common proteins that are implicated in dogs and cats with food allergies are chicken, beef, fish, soy, egg, and dairy. Not all animals are allergic to all of those proteins, but those are just the most common ones that we see causing reactions in dogs and cats with food allergies. It is extremely rare to have a dog or a cat that has a grain allergy. So please don’t go out and switch your pet to a grain free diet because of a concern for food allergies. It is very likely not going to do anything for a potential food allergy, and there have been some risks associated with grain-free diets as far as diet associated cardiomyopathy. 

Chronic infections and inflammation from food allergies can lead to severely red, swollen, and painful ears.

Testing for Food Allergy - The Elimination Diet Trial

[00:08:55] I really wish that there was an easy way for me to diagnose a food allergy. At the time this podcast is being recorded, there are no reliable blood or saliva tests for canine and feline food allergies. Please understand there are blood and saliva tests for food allergies on the market, but at this time, the research has shown that these are not reliable in correlating clinical signs of food allergies. The only definitive way to diagnose a food allergy in dogs and cats is by performing an elimination diet trial under the supervision of your veterinarian. During an elimination diet trial, a pet is fed a specific diet to which their immune system will not react.

[00:09:36] There are several different schools of thought as to which foods to feed, but they’re most often going to either be a hydrolyzed protein diet or a novel protein diet. Hydrolyzed diets are prescription foods in which the original protein source is broken down into very, very short amino acid chains. Amino acids are like the building blocks of proteins.  When a protein is intact, the immune system recognizes that protein and in animals with food allergies an allergic response occurs. If the protein is broken down into short enough amino acid chains, the immune system can no longer recognize the protein and therefore it cannot stimulate an allergic reaction. The same science of hydrolyzed diets is used to provide nutrition to babies that have a milk allergy. 

[00:10:21] Some dermatologists will also perform diet trials with novel protein diets and a novel protein is a protein to which the animal’s immune system has never been exposed. The idea behind this concept is that the immune system hasn’t had a chance to develop an allergic reaction to the novel protein. Unfortunately, there has been some research to demonstrate that there’s cross-reactivity between some of the common novel proteins used and the proteins to which most dogs and cats are commonly allergic to. There are several prescription novel protein diets available, or you can work with a veterinary nutritionist to formulate a home cooked diet specific for your pet.

[00:10:59] I strongly caution against using over the counter diets that claim that they’re single protein or novel protein, because there have been many studies showing contamination of other proteins in over the counter diets, so even if you think that the only protein your pet is eating is salmon based on the ingredients on the label, those studies have shown that there’s often contamination with chicken or beef protein from other diets that are processed on the same equipment in the facility. 

[00:11:25] Whichever diet your veterinarian recommends for the diet trial, it’s important to understand that this diet is not changing the immune system. The food that they’re recommending is going to provide your pet with nutrition while avoiding foods that could potentially be stimulating the immune system. Let me repeat that one more time, because this is the key concept of an elimination diet trial. The prescription diet is providing nutrition while avoiding foods that could be potentially stimulating the immune system. If the pet has a food allergy, it’s still there while they’re eating this food. The concept is just that the prescription food doesn’t stimulate an allergic reaction. So unfortunately, you can’t mix any other foods during the diet trial because the pet is still allergic to those other foods. It’s kind of like feeding a child with a peanut butter allergy, almond butter and jelly sandwiches during the school week so that he has nutrition, but you can’t reward him with a Reese’s peanut butter cup on the weekend. That peanut butter allergy is still there. It’s just that the almond butter doesn’t cause a reaction. There’s no mixing a little bit of chicken in with the prescription diet to encourage the dog to eat it. The dog is still potentially allergic to chicken. 

[00:12:34] The good news is a diet trial doesn’t last forever. Depending on who you talk to, it typically lasts between eight and 12 weeks. Because there’s no blood or saliva tests that’s effective in diagnosing food allergies, I try to explain to pet owners that this is a really long diagnostic test that they’re performing for me at home. At the end of that test, if we can show that the animal does not have a food allergy, then they can go back to feeding whatever makes their pet happy. But if they want the diet trial to be successful during those eight to 12 weeks, no other food passes the animals lips, and that includes foods used to give medications, so if you have a hard time giving medications to your animal without using cheese or hot dogs or other treats, please talk to your veterinarian about alternatives that can be used during the diet trial. I typically start by having pet owners soak some of the kibble from the prescription diet in warm water until it becomes mushy and then put the pill in a makeshift meatball from the mushy kibble. This is the most ideal solution, but there are some other solutions that you can talk to your family veterinarian about. 

[00:13:33] Because it can take six to eight weeks for itch to improve in animals with food allergies alone, I usually prescribe some type of anti-itch medication at the start of the diet trial to make sure my patient’s comfortable. As we get closer to the end of the diet trial, I’d like to see how itchy they are without anti-itch medication. And if the itch is still there, then I’m pretty confident that animal has environmental allergies. They could definitely still have food allergies also, but usually by that time, any itch related to food allergies should have improved on the prescription diet, so any itch leftover is environmental itch. With pets who have environmental allergies, I’ll put them back on an anti-itch medication so that they’re comfortable before I move forward with challenge feeding. If the itch is gone, then we move forward with our challenge feeding without any further medications to confirm our suspicion of a food allergy.

[00:14:23] So with this two to three months diagnostic test that the pet owner is performing for me at home, it’s important for them to understand that the diagnosis of a food allergy is not made by how much better the animal gets at the end of the diet trial, because they could still be allergic to things in the environment. The diagnosis of a food allergy is made by noticing how much worse an animal gets when you challenge feed them with something that they’re allergic to.  What do I mean by challenge feeding? Well, It means re-introduction of a food that the animal was eating prior to starting the diet trial. Usually this is either kibble they were on, or if the pet owner is suspicious that, in the past, chicken has upset their pet’s tummy, we may start by doing a single protein source. But in the beginning, I just want to know, yes or no, is there a food allergy? 

[00:15:11] Pets with a food allergy will typically start to react within two to five days of a food to which they’re allergic, being introduced in the diet. However, there are some pets that will react within a few hours and some can take up to a week. That reaction can involve things like an increase in an itch and redness or swelling of the skin, paws, face or ears. Some animals will also have gastrointestinal signs like soft stool, a loud stomach gurgling,  or that room clearing gas we were talking about before. Food allergies are typically less responsive to anti-itch medications than environmental allergies, so oftentimes even if an animal is receiving an anti-itch medication for environmental allergies, if we can give them a food they’re highly allergic to the anti-itch medication that easily controls that environmental allergy may have a harder time controlling the patient’s allergic reaction to food.

[00:16:04] If there’s no reaction after a week, then, depending on how strict the pet owner was during the diet trial and how confident I am in the diet that was used, I usually say we’re safe to rule out food allergies as an underlying cause of itch in their animal.  If that’s the case, we can go back to feeding whatever makes their pet happy and we move on to addressing environmental allergies, which we’ll talk about in future episodes. 

After Confirming a Food Allergy

[00:16:26] If a food allergy is present, then I work with the client to figure out which proteins are safe and which ones cause a reaction. That can take a lot of time and trial and error to do. I’m a very big fan of spreadsheets, and this is where they come in super handy. Not every pet owner wants to do this and that’s okay. Some animals get really, really uncomfortable when they have an allergic reaction to food, so once the pet owner knows that food is the cause, if the animal likes the diet that they’re on, it is okay to stay on that diet indefinitely if it’s a diet formulated for maintenance, feeding also. Other owners want more information so they can add other foods into their pet’s diet that won’t cause a reaction. Usually these pets have an allergic reaction that’s easier to get back under control. Cookie’s dad was awesome at doing individual ingredient challenges and we were able to find out which proteins he could use when going to obedience and agility class with her

[00:17:21] Long-term treatment of food allergies involves avoidance of the protein that stimulates an allergic reaction. Therefore, I usually recommend a prescription diet, so I can feel confident knowing that there are no contaminant proteins that could stimulate an allergic reaction. If the pet owner really wants to feed a non-prescription food that they’ve tried and hasn’t caused an allergic reaction during challenge feeding, I have them watch very, very closely for any reactions occurring within two to five days of opening a new bag of food, just in case that particular batch may have been contaminated from other protein sources being processed on the same equipment.

[00:17:56] Allergy medications like steroids, Apoquel, Cytopoint, and Atopica can be used to control the reactions if a pet eats something that they’re allergic to, but with food allergies, it typically takes higher doses of these medications in order to calm the allergic reaction. Therefore, it’s important to address the underlying cause of the allergic reaction with avoidance rather than using medication to treat the reaction.

[00:18:19] So just to kind of sum things up for you, allergies are a chronic skin condition, and unfortunately they require a lifelong management. Effective flea prevention is critical for any patient with allergic skin disease. It’s really tough to tell the difference between food allergies and environmental allergies based on the appearance of the animal alone, so working with your veterinarian to figure out what the primary cause is will go a really long way towards minimizing your frustration. It’s possible for animals to have both food and environmental allergies, making a prescription elimination diet trial under the supervision of a veterinarian important for a definitive diagnosis. Itch from allergies can be managed using symptomatic medication, such as Atopica, Apoquel, Cytopoint, and steroids and we’ll talk about all of these medications in upcoming episodes. Long-term management of food allergies is through avoidance of the protein to which the animal is allergic by using a prescription diet.

Scratching the Itch:
Indoor Hunting Feeder

The Indoor Hunting Feeder is the fun and easy way to eliminate common bad behaviors in cats. Manage scarf and barf, alleviate anxiety and destructive behavior, and prevent litter box issues, with this veterinarian designed feeder.

The link in this post is an affiliate link. This means if you click on the link and purchase the item, I will receive an affiliate commission at no extra cost to you. All opinions remain my own.

[00:19:50] I’d like to close each episode with a segment called “Scratching the itch.” The segment is designed to highlight something, whether it’s a human interest story, a product or a website that provides relief, or just makes you feel good. Hence, scratching the itch. Please let me know via the Facebook group or contact me via the website to let me know what you think about the “Scratching the itch” segment and if you have a suggestion for something for us to feature in the future. Today’s “Scratching the Itch” is related to food, but not necessarily food allergies. While most of our pet cats are couch potatoes that love to lounge around, cats are actually excellent hunters who see themselves as tigers on the prowl for their prey. We’ve trained them to eat from their bowls at their set feeding location, but what if there was something that you could do to unlock their inner lion? Well, Dr. Liz Bales, a veterinarian, has created a cat feeding system designed to harness your cat’s natural prey drive. It’s called the indoor hunting cat feeder.

[00:20:46] This feeding system is three little small mice that you fill with a cat’s meal, and then hide the mice around the house. The cat has to hunt for the smell to find its meal. The indoor hunting cat feeder has been shown to prevent bad behavior by improving your cat’s mood and saving your furniture from destruction.

[00:21:04] It will help you sleep through the night because your cat will be off hunting instead of tapping your face to get up and feed them. It stops that scarf and barf that occurs when cats inhale all of their food at once. It decreases stress, which will decrease the problem of urinating outside the litter box. It is an excellent weight management tool, both by making it easier to calculate exactly how much food your cat gets, but it also helps get them off the couch and burning calories. And lastly, it prevents boredom both in your cat and in you while you enjoy watching how much fun they’re having.


  1. Ballardini, Natalia et al. “Anaphylactic Reactions to Novel Foods: Case Report of a Child With Severe Crocodile Meat Allergy.” Pediatrics vol. 139,4 (2017): e20161404. doi:10.1542/peds.2016-1404
  2. Center for Veterinary Medicine. (2019, June 27). FDA Investigates Potential Link Between Diet & Heart Disease in Dogs.
  3. Olivry, Thierry, et al. “Critically Appraised Topic on Adverse Food Reactions of Companion Animals (1): Duration of Elimination Diets.” BMC Veterinary Research, vol. 11, no. 1, Aug. 2015, pp. 1–3.
  4. Olivry, T., Mueller, R.S. “Critically Appraised Topic on Adverse Food Reactions of Companion Animals (4): Can We Diagnose Adverse Food Reactions in Dogs and Cats with in Vivo or in Vitro Tests?” BMC Veterinary Research, vol. 13, no. 1, Aug. 2017, pp. 1–5.
  5. Olivry, T., Mueller, R.S. “Critically Appraised Topic on Adverse Food Reactions of Companion Animals (5): Discrepancies between Ingredients and Labeling in Commercial Pet Foods.” BMC Veterinary Research, vol. 14, no. 1, Jan. 2018, pp. 1–5.
  6. Olivry, T., Mueller, R.S. “Critically Appraised Topic on Adverse Food Reactions of Companion Animals (7): Signalment and Cutaneous Manifestations of Dogs and Cats with Adverse Food Reactions.” BMC Veterinary Research, vol. 15, no. 1, May 2019, pp. 1–6.

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