Food Allergies in Dogs

A food allergy is an over-reaction of your dog's immune system to an unwelcome protein that is present in a particular ingredient of their diet.

Dogs that develop allergies to foods can experience uncomfortable itching of the skin as well as chronic conditions such as ear infections, gas, and wheezing. An allergy is the immune system of the body responding to a perceived threat, in this case an ingredient in the dog's diet.

In order to reliably determine which allergen is affecting your pet, an elimination diet may be recommended. This can be time-consuming, but it's often necessary in order to deduce which ingredient is causing the reaction.

Food allergies in dogs can develop at any age, but the majority of dogs do not acquire food allergies until they are more than 3 years old. Skin reactions are often located around the face or groin, under the front legs, or between the toes.

Symptoms to look for include:

• Bald patches
• Chronic ear infections
• Chronic gas
• Chronically inflamed feet
• Coughing 
• Diarrhea
• Face rubbing
• Head shaking
• Hives
• Obsessive licking
• Paw biting
• Poor puppy or adolescent growth 
• Skin infections
• Skin rashes
• Vomiting
• Wheezing

Types

Food allergy — An allergy to food is a response by the body’s immune system to defend itself against a threat. An allergic reaction doesn’t happen the first time a dog is exposed to the allergen but rather after repeated exposures. Any food can cause an allergic reaction, but foods such as beef, dairy, chicken, and eggs tend to cause allergies in canines more often than others.

Food intolerance — While a food allergy is the body’s immune system reacting to what it perceives as a threat, food intolerance has no immune involvement. An intolerance to a food type is more likely to cause a gastrointestinal response than allergies do. Additional symptoms, such as a change in the consistency or color of the stools and gurgling sounds from the digestive system, are common with a food intolerance.

Allergies of all sorts are due to an abnormally strong defensive response to a protein that the immune system considers to be an invasive substance. It is estimated that around 60-70 percent of our immune system cells actually reside in the digestive system, and the same applies to our dogs.

The process of digestion is designed to break down our foods into their smallest parts, which are known as amino acids. These amino acids are then absorbed by white blood cells called enterocytes. When proteins are not properly broken down during digestion, these enterocytes see them as intruders and attack. Over time the response of these cells becomes more aggressive and symptoms intensify. 

Although any food can become an allergen, some foods are more likely to generate a reaction than others. Frequent offenders for dogs can include:

• Beef
• Chicken
• Corn
• Dairy products
• Eggs
• Fish
• Lamb 
• Soy
• Wheat

The symptoms that your dog shows due to an allergic reaction will prompt your veterinarian to collect skin scrapings from any affected areas for cutaneous cytology. Cutaneous cytology is the microscopic evaluation of the skin cells to look for problems like mites, yeast infections, or signs of disease. When these are not found on the dermal cells, a food allergy may be suspected.

In order to confirm the allergy, an elimination diet is usually implemented. An elimination diet usually involves changing the dog's food to either a reduced ingredient commercial food or a diet of bland human food, such as a boiled protein and a simple carbohydrate like rice.  

Novel ingredients, which are proteins and carbohydrates that are not common in the dog’s current diet, are generally used for an elimination diet. All of the ingredients in your dog's current food should be avoided when determining the proper replacement food.

In many cases, it may be the entire food family that your pet is reacting to, so switching from a chicken diet to a mammalian source such as rabbit may have better results than switching to another avian species like duck.

If the symptoms are caused by an allergy, a properly implemented elimination diet will cause them to cease. Once this has occurred, extra ingredients will be slowly added into the diet until the allergen is identified. During this time, it is essential to ensure your dog does not ingest anything other than the food used for the elimination diet. A single treat with the allergen can cause the allergy to resurface. Sources to avoid include:

• Cow hooves
• Flavored medications (including heartworm preventives) or supplements
• Flavored plastic toys
• Flavored toothpastes
• Pigs' ears
• Rawhides
• Treats

Traditionally, an elimination diet will need to be fed for around 8-12 weeks to determine the cause of your dog's food allergy. However, a 2021 study showed that it may be possible to shorten the length of this diet trial period by administering prednisolone during the first 2-3 weeks of the trial.

During the study, 39 dogs received prednisolone for the first 2-3 weeks of an elimination diet. Medications were then discontinued for 2 weeks before the dogs were then fed their original diet. If they relapsed, prednisolone was given for an additional week. Of the 21 dogs determined to have food allergies, 14 of them did not relapse after the medication was stopped, while 6 dogs had a single relapse and 1 dog relapsed twice.

So while it's still time-consuming to feed an elimination diet, it may be possible to speed up the process and reach an accurate diagnosis in a much shorter time frame.

It can take several weeks for the elimination diet to reveal the offending allergen, and your pet may still be experiencing some symptoms during this time.

Corticosteroids may be recommended by your veterinarian to reduce swelling, along with antihistamines to calm the itching. Use of these treatments may make it harder to determine which ingredient in your dog’s diet is causing the reactions by masking allergic symptoms, so many veterinarians prefer to complete the elimination diet before prescribing these types of medications. Secondary skin infections are commonly seen with food allergies, and antibiotics may be prescribed to combat this problem.

Once the allergen has been identified, the initial course of action is avoidance of the ingredient. Other supplements, such as omega-3 oils and probiotics, may also be recommended after the elimination diet is completed to support the immune system. This will help your dog to handle any accidental exposure to allergens and to prevent the cultivation of new allergies.

Allergies to foods are not curable, but symptoms usually cease if the allergen is removed from the animal’s diet. Any exposure to the allergen can cause a relapse, so care must be taken in the type of treats and flavorings you use for your dog.

Unfortunately, if your canine has had an allergic response to one type of food they are more likely to  develop an allergy to the ingredients in the replacement diet over time as well. The approach to combat this situation varies within the veterinary profession, with some vets recommending that your pet remain on a single source of dog food for allergies, while others maintain that a steady rotation of 3 or 4 novel protein sources is optimal.

Food allergies can be expensive to treat. If you suspect your dog is at risk of food allergies, start searching for pet insurance today. Wag!’s pet insurance comparison tool lets you compare plans from leading companies like PetPlan and Embrace. Find the “pawfect” plan for your pet in just a few clicks!