Itchy skin? Repeat ear infections? Diarrhea? Your dog’s symptoms may be caused by a food allergy or an intolerance to something in their diet. “Surely it can't be that,” you might be thinking. “My dog has eaten the same food for ages and has just started having these problems.”
It turns out that dogs are actually more likely to have adverse reactions to foods that they’ve eaten for a long time. Keep reading to learn more about dog food allergies and intolerances, why they cause the symptoms they do, and science-backed ways to help your dog feel better.
Key Points About Food Intolerances and Allergies in Dogs
- Food allergies and intolerances often arise in response to food your dog has been eating for a while (so the food does not have to be new).
- The terms “food sensitivity” and “food intolerance” refer to the same issue, which is trouble digesting a certain ingredient.
- The term “food allergy” refers to an immune response your dog has to a specific ingredient.
- However, despite this distinction, the symptoms of food intolerances and food allergies in dogs can be very similar.
- Elimination diets are the most reliable way to identify whether an ingredient is causing the food allergy or intolerance.
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Avoiding the offending food and supporting your dog’s gut health with specific supplements can ensure they find relief and live a happy, healthy life.
What Exactly Is a Food Allergy vs. Food Intolerance?
Understanding the difference between food allergies and food intolerances is crucial for helping your dog, and it all comes down to whether their immune system is the initial trigger.
Food Allergies: When the Immune System Overreacts
A food allergy is an immune response to something the body repeatedly and mistakenly perceives as a threat.
Think of your dog’s immune system as an overzealous security guard. When a problem food allergen shows up (for example, chicken protein), this “security guard” unnecessarily sounds the alarm and calls for backup, producing special proteins called antibodies. These antibodies then trigger the release of histamine and other inflammatory chemicals that travel throughout the body.
Food allergy symptoms can be severe, even with tiny amounts of the allergen. Food allergy symptoms may also worsen over time with repeated exposure.
The immune system reaction associated with a food allergy can cause symptoms anywhere in your dog’s body, from itchy skin to ear infections to digestive upset, because the immune response travels through the bloodstream and throughout the body.
In rare cases, food allergies can cause anaphylaxis. This is a severe, life-threatening reaction where the immune system goes into overdrive. Signs of anaphylaxis include difficulty breathing, severe swelling (especially of the face and throat), collapsing, or loss of consciousness. Though anaphylaxis from food is uncommon in dogs compared to humans, when it does occur, it requires immediate emergency veterinary care.
Food Intolerances: When Digestion Goes Wrong
A food intolerance (also called a food sensitivity) doesn’t involve an immune system trigger. Instead, it’s simply your dog’s digestive system having trouble breaking down or processing a particular ingredient. Think of it like a broken key trying to fit into a lock: the digestive system just can’t handle that specific food component properly.
The classic example is lactose intolerance, where dogs (and humans) lack enough of the enzyme lactase to properly digest the sugar in milk. This leads to digestive symptoms like diarrhea, gas, and stomach upset.
Food intolerance is usually dose-dependent, meaning that more of the problematic food leads to more severe symptoms. In some cases, small amounts of the ingredient may not trigger a reaction, but larger amounts would.
Initially, food intolerance symptoms are limited to the digestive system because it is a digestive issue. But after some time, your dog’s gut may become inflamed due to a food intolerance. This can cause issues such as itchy skin and inflammation. We will explain why this happens further on.
Why the Terms (and Symptoms) Get Confusing
You might see “food sensitivity” and “food intolerance” used interchangeably, and that's because they essentially mean the same thing. Both terms describe adverse food reactions that aren’t triggered by the immune system. A food allergy is different, and always begins with an immune system reaction.
True food allergies are actually quite rare in dogs. A study published in the journal BMC Veterinary Research found that genuine food allergies occur in only 1 - 2% of dogs. However, food intolerances and sensitivities are much more common, and they can produce many of the same uncomfortable symptoms.
Common Food Allergy and Intolerance Symptoms
- Itching (most often of the ears, paws, rear end, and belly)
- Sneezing
- Hot spots
- Hives
- Skin rashes
- Eye discharge
- Red eyes
- Hair loss
- Chronic ear infections
- Swollen face, lips, eyelids, or ears
- Gastrointestinal signs (such as flatulence, bloating, vomiting, and diarrhea)
Because the clinical signs of food allergies and food intolerance symptoms have so much overlap, your veterinarian (DVM) can help determine which type of reaction your dog is experiencing.
The Effect of Food Allergies and Intolerances on Your Dog’s Skin
Food Allergies and the Skin
Many dog parents are surprised to learn that some food allergies show up as skin issues, including itchiness, flakiness, and even skin infections.
This is because when your dog’s immune system detects a food allergen, it releases histamine as part of its defense response. Histamine acts like a chemical messenger that causes several reactions:
- Blood vessels widen, increasing blood flow and causing redness and swelling
- Blood vessel walls become “leaky,” allowing fluid to seep into surrounding tissues and create hives
- Nerve endings get stimulated, creating an uncomfortable, itchy sensation
The inflammation from allergic reactions also creates a warm, oily environment on your dog’s skin. This encourages the overgrowth of certain yeasts naturally found on dogs. When this happens, a dog can get what’s called dermatitis, a secondary skin infection from an allergic response.
Food Intolerances and the Skin
While food intolerances don’t arise from immune responses, they can still cause skin symptoms like itching through other pathways — particularly via what’s called the gut-skin axis.
The gut-skin axis is the communication pathway between your dog’s digestive system and their skin. When food intolerances cause gut inflammation or disrupt the gut microbiome, this can weaken the intestinal barrier, allowing inflammatory compounds to leak into the bloodstream (creating “leaky gut”) and travel to the skin. This often causes itching and irritation.
The gut-skin connection is why maintaining a healthy gut microbiome is so important for managing both food allergies and intolerances. When the gut microbiome is balanced, it helps maintain a strong intestinal barrier, reduces inflammation, and supports overall skin health.
This is why gut health interventions often improve skin symptoms regardless of whether the skin symptoms are caused by allergies or intolerances.
The Most Common Food Allergens and Problem Foods for Dogs
Proteins are the culprit for the majority of dog food allergies, while carbohydrates and additives more commonly cause food intolerances.
Most common food allergens: For dogs, these are beef, chicken, and dairy products. This isn’t because these foods are inherently more allergenic — it’s simply because they’re the most common ingredients in commercial dog food, giving dogs more opportunities to develop allergies over time.
The complexity of protein allergies: A single protein source can contain multiple different allergens. For example, a recent study published in the Veterinary Dermatology journal identified 8 different chicken allergens relevant to dogs. Furthermore, the same allergen can exist across different protein sources — this is called cross-reactivity.
Until recently, scientists believed cross-reactivity only happened between similar species (like different types of poultry). However, a 2022 study revealed that the same allergens can span across fish, mammals, and even plants, making elimination diets more challenging.
Other common problem foods: Dog allergies and intolerances to egg, soy, wheat, potato, peas, lamb, pork, rabbit, and fish have also been identified, though these are less common. Research suggests that some breeds may be more prone to food allergies than others, including Boxers, Bulldogs, and Retrievers.
Other Types of Allergies
Mites and fleas are actually the most common cause of allergies in dogs. An allergic dog’s immune system reacts to the insect saliva, causing intense itching. Environmental allergies, such as pollen, dust, and mold, are also relatively common in dogs. Allergens can trigger a dog’s immune system by being ingested, touched, or inhaled. Environmental allergens can sometimes lead to atopic dermatitis, also known as atopy or canine atopic dermatitis (CAD), a chronic, itchy skin disease.
Dogs with other types of allergies are more susceptible to food allergies and intolerances because their immune systems more readily shift into a hyperactive state. Chronic inflammation, whether from a condition like inflammatory bowel disease (IBD) or long-term exposure to allergens, can also cause the immune system to become more sensitive to certain food proteins.
How Are Food Allergies and Intolerances Diagnosed?
Your veterinarian may want to run blood tests or conduct allergy testing, but studies show that these aren’t always accurate in diagnosing food allergies and intolerances in dogs. The only reliable way to diagnose a food allergy or intolerance is through a diet trial.
Diet Trials
Also called an elimination trial or food trial, a diet trial involves switching your dog to a completely new food to eliminate exposure to potential problem ingredients. Once your dog’s symptoms fully improve (usually in 8-12 weeks), you slowly reintroduce ingredients one by one from your dog’s previous diet. Whichever ingredient causes symptoms to return is identified as the culprit.
Seems simple enough, right? Not so fast. It can be challenging (and expensive!) to find novel protein and carbohydrate sources that your dog has never eaten before. Remember, cross-reactivity means the same allergen can be present in different protein sources, and some dogs may have multiple food allergies or intolerances, making it harder to find a suitable new diet. Many dogs are also sensitive to diet transitions themselves, which can add more time and symptoms to the process.
Some dogs can benefit from commercially available hydrolyzed protein diets, where the animal protein has been broken down into molecules small enough that they’re unlikely to trigger immune responses.
Wait, What Is A Novel Protein?
Since the majority of dog food allergies come from protein sources, finding a novel protein is crucial for hypoallergenic diets. A novel protein is simply a protein source that’s completely new to your dog.
Insect protein has attracted increasing attention in recent years for hypoallergenic diets and as a more sustainable protein source. Crickets, for example, are just as digestible as traditional protein sources for dogs. They also support a diverse gut microbiome.
While no food is inherently hypoallergenic or completely “allergy-proof,” research published in the Journal of Animal Science found no allergic reactions or adverse effects in adult dogs fed cricket meal in long-term trials. Conversely, mealworms have been found to trigger allergic reactions in dogs with mite allergies, highlighting the importance of careful protein selection.
Best Dog Food Options for Allergies and Intolerances
There’s a wide range of pet food options for dogs that have food allergies or need an elimination diet trial. Here’s some to consider:
Limited ingredient diets: These, as the name suggests, use as few ingredients as possible. This is usually the first port of call if you don’t know which ingredient is causing your dog’s symptoms. Limited-ingredient pet food can be purchased commercially or made at home with veterinary guidance.
Prescription hypoallergenic diets: These often feature novel proteins like kangaroo or alligator, and can be expensive. While preservatives, artificial colors, and flavorings rarely cause true allergies, they can sometimes trigger food intolerances or sensitivities — so hypoallergenic dog food often boasts all-natural ingredients.
Professional guidance: Since the same allergens can occur across different protein and carbohydrate sources, a veterinary nutritionist can help you choose the best ingredients to increase the chances that your dietary modification works the first time.
Always consult your veterinarian when trying new foods for your dog, especially if they have a history of food allergies or intolerances.
What Dog Parents Can Do About Food Allergies and Intolerances
Switch Up The Protein Source
Since food allergies and some intolerances develop over time with repeated exposure, pet owners can reduce risk by periodically rotating protein sources – every year or so. Rotational diets are an excellent preventative strategy that can help prevent both food allergies and intolerances, while reducing the risk of nutrient deficiencies. The dietary variety from rotational diets also supports a diverse gut microbiome.
This approach involves feeding three or four different brands of dog food with different protein sources in a slow rotation. Once you’ve established diets your dog tolerates well, transition gradually between them every two to three months.
Take A Gut Health Test
Your dog’s gut plays a crucial role in the functioning of their immune system, with 70-80% of immune cells living in the intestinal tract. When gut bacteria become imbalanced, dogs are more likely to develop allergies, intolerances, and other health conditions.
Gut Microbiome Testing provides important information about your dog’s gut bacteria. For example, the Gut Health Test for Dogs can detect bacterial imbalances and identify problematic bacteria associated with inflammation and allergic conditions. It also offers actionable insights to improve your pet’s health.
Give Supplements
Supplements can boost your dog’s immune system and digestive health, potentially helping with both allergies and intolerances. Research suggests that dogs with food allergies and intolerances may benefit from omega-3 fatty acids and biotic supplements.
- Prebiotics (like those in Complete Fiber Blend for Cats and Dogs) feed beneficial bacteria and keep the microbiome diverse and balanced.
- Probiotics (like those in S. boulardii + FOS Powder for Cats and Dogs) improve immune function by releasing anti-inflammatory molecules in the gut.
- Postbiotics (like those in Super Shield Chews for Cats and Dogs) provide important immune-boosting compounds to keep your dog’s immune system strong and hardy.
Learn more about the benefits of biotic supplements here.
Consider A Fecal Transplant
A fecal microbiota transplant (FMT) may be an option for dogs with long-term symptoms that don’t respond well to other treatments. An FMT transfers a complete, balanced community of gut microbes from a healthy donor dog to your dog.
A large body of scientific research has shown that FMT can address a variety of issues associated with an imbalanced gut microbiome, including immune system issues, skin problems, and digestive disorders. FMT from a screened, healthy donor is a safe and effective way to reintroduce missing important bacteria that are key to your dog’s health.
Some veterinarians can perform a fecal transplant procedure via an enema or nasogastric tube. However, sedation is often required, and the expense and risks associated with sedation aren’t ideal for many pet parents. Luckily, oral FMT capsules, like the Gut Restore Supplement for Dogs, are just as effective, and just as safe.
Talk With Your Veterinarian
Food allergies and intolerances in dogs can be managed successfully with proper diagnosis, dietary changes, and regular monitoring. Your veterinarian is your best resource for getting to the bottom of your dog’s health issues and discussing preventative strategies.
Frequently Asked Questions
What is the most common food intolerance in dogs? Food ingredients most likely to contribute to food intolerances and sensitivities in dogs are beef, dairy products, chicken, wheat, and lamb.
How do you fix a dog with food intolerance? The most effective approach is identifying and eliminating the problem ingredient through an elimination diet trial, then maintaining a diet that avoids the trigger food. Supporting their gut health with probiotics and prebiotics can also help both treat and prevent food sensitivities in dogs.
What are the main symptoms of food intolerance in dogs? The four most common symptoms are: digestive upset (diarrhea, gas, vomiting), skin itching and irritation, chronic ear infections, and general discomfort after eating.
How do you know if a dog has food sensitivity? Food sensitivities (intolerances) typically cause digestive symptoms within an hour of eating the problem food. A veterinarian-supervised elimination diet trial is the most reliable way to confirm a food sensitivity.
How long does a food allergy or intolerance take to show up in dogs? Food intolerances usually cause symptoms within an hour of eating. Food allergies can show symptoms anywhere from minutes to several hours after eating. In both cases, symptoms may worsen over time with repeated exposure.