Itchy skin? Repeat ear infections? Diarrhea? Your dog’s symptoms may be caused by a food allergy 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 more likely to have adverse reactions to food they’ve eaten for a long time. Keep reading to learn more about dog food allergies, why they cause the symptoms they do, and science-backed ways to make them better.

An allergy is an immune response to something the body repeatedly and mistakenly perceives as a threat. When an allergen shows up, the immune system overreacts by producing antibodies that then trigger a release of histamine and other chemicals. 

In the case of food allergies, the offending allergens are in a dog’s diet. Food allergies are not very common in dogs but are becoming more prevalent. A study published in the journal BMC Veterinary Research found that true food allergies occur in only 1%–2% of dogs. Instead, dogs are far more likely to have a food sensitivity, which has many of the same symptoms as food allergies.

A food sensitivity, also called a food intolerance, does not involve an immune system response and is instead caused by difficulty digesting a particular ingredient. One example (in both humans and dogs) is lactose intolerance, an inability to digest milk products well.  

So how do you know if your dog has a food allergy or a food sensitivity? Typically, a dog with a food sensitivity will show gastrointestinal symptoms, such as diarrhea or flatulence, within an hour of eating an allergen. Food allergies, in addition to GI symptoms, can show up as an immune reaction anywhere in the body. Because there is a lot of overlap of symptoms between the two, your veterinarian can help figure out what is going on.

• 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 problems (such as flatulence, vomiting, and diarrhea)

Many dog parents are surprised to learn that food allergies show up as skin issues, including itchiness, flakiness, and even skin infections. Histamine, which the immune system releases in response to an allergen, is to blame. 

Histamine causes blood vessels to dilate, which increases blood flow and leads to redness, swelling, and itching. It also increases the permeability of blood vessels, allowing fluid to leak into the surrounding tissues, causing hives or other skin reactions. Additionally, histamine can stimulate nerve endings, leading to an itchy sensation in the skin. 

Some types of yeast that are normally found on dogs’ skin thrive in the heat and excess oil produced during an inflamed state. When they overgrow, a dog can get what’s called dermatitis, a secondary skin infection from an allergic response.

Proteins are the culprit for a large majority of dog food allergies. The most common allergens in dog food are found in beef, chicken, and dairy products. It’s not that these food items are especially allergenic; it’s because they are the ones most prevalent in commercial dog food.

A single protein source can contain multiple allergens. For example, a recent study published in the Veterinary Dermatology journal found 8 different chicken allergens relevant to dogs. Furthermore, the same allergen can exist in different protein sources. This is called cross-reactivity. 

Until recently, scientists believed that cross-reactivity only happened between similar species, such as mammals or poultry. However, a 2022 study highlighted that the same allergens can span across fish, mammals, and even plants.  

Dog allergies to egg, soy, wheat, potato, peas, lamb, pork, rabbit, and fish have also been identified, although these are not as common. Research suggests that some breeds may be more prone to food allergies than others, including Boxers, Bulldogs, and Retrievers.

Mites and fleas are the most common allergies in dogs. A dog’s immune system reacts to the insect salvia, which causes 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, touching their skin, or by being inhaled. 
Dogs with other types of allergies are more susceptible to food allergies because their immune systems can more easily shift into a hyperactive state. Chronic inflammation, whether from a condition like inflammatory bowel disease (IBD) or long-term exposure to allergens, can cause the immune system to become more sensitive to certain food proteins.

Your veterinarian may want to run blood tests or conduct allergy testing, but studies show that this isn’t always accurate in diagnosing food allergies in dogs. The only true way to diagnose a food allergy is through a diet trial. 

Also called an elimination trial or food trial, a diet trial involves switching your dog to a new food to reduce the possibility of food allergen exposure. 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 one causes an adverse reaction is determined to be the food allergy or food sensitivity. 

Seems simple enough, right? Not so fast. It can be hard (and not to mention expensive!) to find a novel protein and carbohydrate source that your dog has not eaten before. Remember, the same allergen can be present in a different protein source (cross-reactivity) and some dogs may have multiple food allergies, making it more difficult to find a suitable diet. Many dogs are sensitive to diet transitions, which can add more time and even more symptoms to the process. 
Some dogs can benefit from commercially available hydrolyzed diets in which the animal protein has been broken down into molecules small enough that they are unlikely to cause an immune response.

The large majority of dog food allergies come from protein sources, so finding a novel protein is a big focus for hypoallergenic diets. A novel protein is just a protein source that’s new to your dog, including ones that aren’t similar to the protein source. For example, if your dog’s diet had chicken in it, venison would be a much better option than turkey for a novel protein. 

Insect protein has attracted increasing attention in recent years for hypoallergenic diets and a more sustainable protein source. Crickets, for example, are just as digestible as more traditional sources of protein for dogs and support a diverse gut microbiome in dogs. 
While no food is inherently hypoallergenic or completely allergy-proof, research published in the Journal of Animal Science found no allergic reactions or other adverse effects in adult dogs who were fed cricket meal in a long-term trial. Conversely, mealworms have been found to trigger an allergic reaction in dogs that have a mite allergy. 

There is a wide range of pet food options for dogs that have food allergies or need an elimination diet trial. So, which one should you choose?

You want to first consider a limited ingredient pet food. If you don’t know which ingredient is causing your dog’s symptoms, it’s best to keep their new diet as simple as possible. These can be purchased or homemade; your veterinarian can help you decide what is best for your dog – and your wallet.

Always consult your veterinarian when trying a new food for your dog.

Prescription hypoallergenic diets often boast all-natural ingredients. Preservatives, artificial colors, and flavorings in your dog’s food are unlikely to cause true allergies, although these ingredients sometimes trigger sensitivities or adverse reactions. Sourcing novel proteins, like kangaroo or alligator, can make these diets expensive, but worth it. 

The same allergens can occur in different protein and carbohydrate sources often found in dog food. A veterinary nutritionist can help you choose the best ingredients to increase the chances that your dietary modification works the first time. 

We know that food allergies build over time and we know that protein sources cause the majority of food allergies in dogs. Therefore, pet owners can avoid food allergies by switching up the protein source every year or so to reduce allergen exposure. 

Rotational diets are a great preventative strategy that pet parents can use to prevent food allergies in their dogs and reduce the risk of long-term health problems caused by an ongoing nutrient deficiency. The dietary variety from rotational diets also supports a diverse gut microbiome. 

This approach involves feeding three or four different brands of food with different protein sources in a slow rotation. Once you’ve established three or four different diets that your dog tolerates well, transition your dog gradually from one of these diets to the next every two or three months.

Your dog’s gut plays an important role in your dog’s immune system function, with 70-80% of immune cells living in the intestinal tract. If the community of gut bacteria becomes imbalanced, your dog is more likely to develop allergies and other health conditions. 
Gut Microbiome Testing gives you important information about the state of your dog’s gut flora. For example, the DoggyBiome Gut Health Test can detect bacterial imbalances and identify problematic groups of bacteria associated with inflammation and allergic conditions. It also comes with actionable insights about how you can improve your dog’s gut health and immune function.

Supplements are an easy way to boost your dog’s immune system, which is best done by way of supporting gut flora. Research suggests that dogs with food allergies may benefit from supplements such as omega-3 fatty acids and biotics. 

Prebiotics, like those found in DoggyBiome™ Gut Cleanse Powder, feed beneficial bacteria and keep your dog’s microbiome diverse and balanced. Probiotics, like those found in DoggyBiome™ S. boulardii + FOS Powder, improve immune function by releasing anti-inflammatory molecules in the gut. Postibiotics, like those found in the delicious DoggyBiome™ ImmuneShield™ chews, introduce important compounds for proper immune system function. 

Learn more about the benefits of biotic supplements here.

A fecal microbiota transplant (FMT) may be an option for your dog if they have long-term symptoms that don’t respond well to medication. An FMT is a procedure that transfers a complete and balanced community of gut microbes from a healthy donor to a sick recipient. A large body of scientific research has shown that FMT can resolve a variety of symptoms associated with an imbalance of the gut microbiome, including immune system issues, skin problems, and digestive disorders.
FMT is a safe and effective way to reintroduce missing important bacteria that strengthen immune system function. Some veterinarians can perform a fecal transplant procedure via an enema or nasogastric tube. However, the expense and risks associated with the required sedation aren’t ideal for many pet parents. Luckily oral FMT capsules, like DoggyBiome Gut Restore Supplement, are just as safe and effective.

Can you please explain the pros and cons of making my dog’s food at home compared to paying for specialty pet food? 

What are some tips on doing a food trial when I have multiple pets in the house?

If I want to avoid medication for my dog’s allergies, what other options do you suggest? 

I heard that prebiotics, probiotics, postbiotics, and fecal transplants could help improve my dog’s food allergies. What are your thoughts about this?  

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