Food Allergies and Intolerances in Dogs

Adverse food reaction (AFR) in dogs is the term used to describe an abnormal response to a certain ingredient in a food. 

There are two main types of AFRs in dogs: food allergy, where the immune system inappropriately overreacts to a certain protein trigger, and food intolerance, which causes symptoms without involving the immune system. 

While the underlying causes differ, dog food allergies and food intolerances can have similar clinical signs and are diagnosed similarly. Both are typically treated with a change in diet, such as switching to a hydrolyzed protein diet.  

What Are Food Allergies in Dogs?

Dog food allergies are less common than environmental allergies, such as seasonal allergies and flea allergies. 

A food allergy in dogs is when the immune system overreacts to an allergen (most commonly a protein) that the dog has previously been exposed to. This can cause symptoms such as itching, skin infections, ear infections, and sometimes digestive upset (vomiting and diarrhea).  

While many dogs with food allergies are over 1 year old, dogs of any age can develop a food allergy to a protein they have been eating for a long period of time with no previous problems.  

For a dog to have developed a food allergy to a specific protein, the dog must have eaten that protein in the past.  

Food sources that most commonly cause food allergies in dogs are:   

• Beef   
• Dairy  
• Chicken   

Food sources that cause food allergies in dogs less commonly include:   

• Wheat  
• Lamb   
• Soy  

What Is Food Intolerance in Dogs? 

Food intolerance happens when a dog has an adverse reaction to a food or ingredient that does not involve the immune system. It commonly causes digestive upset, including vomiting, diarrhea, gas, and low energy. 

Food intolerance reactions can happen after the first exposure to a certain food item. Also, digestive upset symptoms may worsen if your dog eats larger amounts of the triggering ingredient. 

Common triggers can include: 

• Rich or high-fat foods: Greasy table scraps, treats, or dog foods containing high levels of fat. 
• Dairy: Many dogs do not digest lactose well. 
• Certain food ingredients or additives 

Speak with your vet to help figure out what may trigger your dog to have food intolerance. 

Symptoms of Food Intolerance and Food Allergies in Dogs

Dog food allergy symptoms and symptoms of food intolerance in dogs can overlap.  

General guidelines for symptoms associated with food allergy and food intolerance include:  

Skin reactions (food allergy): 

• Itchy and/or red skin 
• Ear infections 
• Skin infections 
• Hair loss 
• Licking or chewing paws 

Gastrointestinal reactions (both food allergy and intolerance): 

• Diarrhea 
• Vomiting  
• Excessive gas (flatulence) 
• Weight loss  
• Decreased energy (lethargy) 

Causes of Food Allergies and Food Intolerance in Dogs

The cause of food allergy in dogs is complex and not fully understood, possibly having a genetic component. It is unknown why the immune system becomes hypersensitive to a certain food protein over time. Food allergies can occur at any age but more commonly occur in older dogs. 

Food intolerance does not involve the immune system and can result from certain foods or ingredients that a dog cannot properly digest or tolerate. Food intolerance can occur at any age, and symptoms may worsen the more the dog eats of the trigger. 

How Veterinarians Diagnose Food Allergies and Food Intolerance in Dogs

Veterinarians diagnose food allergies and food intolerance in dogs using a diet elimination trial (also known as a hypoallergenic diet trial) using these steps: 

• Choose a therapeutic hypoallergenic diet recommended by your vet. 
• Over a two-week period, gradually transition your dog’s food from their original diet to the new hypoallergenic diet. 
• Feed the hypoallergenic diet exclusively for eight weeks or more, as directed by your vet.  
• Reintroduce your dog’s original diet to check for recurrence of their symptoms. 

No food other than the prescribed diet should be fed during the trial period, including other pet food, treats, table scraps, flavored medications, supplements, or edible chews, because these can compromise the trial. 

For suspected skin-related food allergies, diet trials generally last eight to 12 weeks, while gastrointestinal signs may respond to a shorter trial. If symptoms improve, reintroducing the dog’s previous diet and seeing the symptoms return is necessary to confirm a food allergy. 

It is important to note that while there are blood/saliva and hair/saliva tests that claim to diagnose food allergies, none have been shown to reliably diagnose food allergy in dogs.  

Treatment of Food Allergies and Food Intolerance in Dogs

The treatment for food allergies and food intolerance generally involves avoiding the food or ingredient causing the adverse reaction. This is often achieved by feeding a limited ingredient or hypoallergenic diet prescribed by your vet. 

The first diet your vet recommends may work great for your dog, but sometimes it takes time and patience to work through different diets to find the one that works best. 

Prescription Hydrolyzed Protein Diets 

• A hydrolyzed protein diet contains proteins broken into small pieces that are less likely to trigger an immune system response. 
• Prescription hydrolyzed diets are manufactured under strict conditions to minimize cross-contamination with other protein sources. 
• They often are supplemented with high levels of omega fatty acids, which help decrease inflammation and support skin and digestive health. 

Your vet may prescribe a hydrolyzed protein diet, such as: 

• Purina Pro Plan Veterinary Diets HA Hydrolyzed 

• Hill’s Prescription Diet z/d Skin & Food Sensitivities 

• Royal Canin Ultamino  

Amino acid-based diets are the strictest type of hypoallergenic diet, providing protein in its simplest form: amino acids, with the dietary protein antigen completely removed. These diets are known as “elemental diets,” such as Purina Pro Plan Veterinary Diet EL Elemental. 

Prescription Novel Protein Diets 

• A novel protein diet contains protein and/or carbohydrate sources that the dog has never eaten before, such as venison, duck, rabbit, or even alligator, so your dog’s immune system should not overreact to them. 
• Prescription novel protein diets are manufactured under strict conditions to minimize cross-contamination with other protein sources. 
• They often are supplemented with high levels of omega fatty acids, which help decrease inflammation and support skin and digestive health. 

Your vet may prescribe a novel protein diet, such as: 

• Purina Pro Plan Veterinary Diets DRM Dermatologic Management 

• Hills Prescription d/d Skin/Food Sensitivities 

• Royal Canin Selected Protein  

Recovery and Management of Food Intolerance and Food Allergies in Dogs

It is important to work with your vet to find a diet that keeps your dog healthy and free from symptoms. 

If your dog has a food allergy or food intolerance, dedicating time and patience to a strict elimination diet trial can help identify a food that works best for your dog. Once the triggering food or ingredient has been identified, long-term management involves avoiding it. 

A study has shown that when feeding a strict hypoallergenic diet, 85% of dogs improve by five weeks, and >95% improve by eight weeks. 

Gastrointestinal signs may resolve more quickly (often within one to two weeks) than skin and ear signs, which can take up to eight weeks to improve.