Food Allergies in Dogs: How to Spot and Eliminate Them

Skin issues are one of the most common reasons we take our dog to the vet. The main symptoms we might notice are itching, hair loss, or redness of the skin.

When our dog scratches more than usual, the first thing we think is that it might have fleas or an allergy to something in the environment. But did you know that itching is also the main symptom of food allergies?

Below, we'll learn a bit more about this type of food-related allergy, answering a series of questions in simple terms.

What Is a Food Allergy?

A food allergy is an adverse reaction to a specific food that causes skin and/or digestive symptoms in the dog. When a dog has a food allergy, what we usually see is that it scratches more than usual.

Gastrointestinal symptoms can also appear, such as diarrhea, looser stools, gas, or even vomiting. However, these digestive signs are only seen in 20% of cases.

In allergic dogs, the skin can be red and show lesions caused by scratching. The distribution of these lesions varies, but they're commonly seen on the paws, armpits, groin, perineum, face, ears, and neck. These dogs also often suffer from ear infections.

Why Do Some Dogs Develop Food Allergies?

In animals with no underlying health issues and no food allergies, food is eaten, digested, and absorbed through the digestive system without any abnormal reactions.

What happens in a dog with a food allergy is that, upon eating a particular food, the body identifies it as potentially harmful. Its immune system reacts by releasing a series of substances responsible for the animal's allergy symptoms.

Allergies can be seen as a malfunction of the animal's immune system, since its defenses react to something that isn't actually harmful to the body — food.

It's worth noting that any food eaten can trigger an allergic reaction, but the part of the food responsible for this reaction is protein. To date, no food allergy to carbohydrates or fats has been described.

Generally speaking, the foods most likely to cause a food allergy are those with a high protein content that are eaten more frequently.

Between 35-50% of dogs with food allergies are allergic to more than one ingredient, with the most common being: beef, dairy products, chicken, corn, wheat, fish, or soy.

Which Dogs Tend to Develop Food Allergies?

Food allergies aren't tied to any specific breed, age, or sex. It's an individual condition, and any dog can develop it at some point in its life. The age at which the first signs appear varies, ranging anywhere from four months to eleven years old.

How Can I Tell If My Dog Has a Food Allergy?

Food allergies are hard to identify, since their symptoms resemble those of other diseases, which is why it's important to see a vet to confirm that our dog's symptoms are, in fact, due to a food allergy.

To determine whether a dog has a food allergy, the vet will first rule out other health problems, such as parasites, infections, etc.

A definitive diagnosis is reached through an elimination diet, which involves feeding the dog a food free of allergens or based on proteins it hasn't eaten before.

There are two types of elimination diets: those based on novel proteins (proteins not typically used in dog food, such as venison, rabbit, or insects) and those made up of hydrolyzed proteins, meaning proteins that have been broken down into very small particles that won't be detected by the animal's immune system.

The time needed to confirm whether a food allergy is present is at least 6 weeks, so during this period it's very important that the dog eats only the elimination diet. Generally, improvement in symptoms should be seen after 3-4 weeks on this diet.

What to Do After the Elimination Diet?

Animals that show a full improvement in symptoms on the elimination diet should undergo a challenge test, which involves feeding them their original diet again, the one they ate before treatment. If allergy signs reappear once they're back on their regular kibble, we can confirm that our dog has a food allergy.

How to Know Which Ingredient It's Allergic To?

If we want to take the diagnosis a step further and find out which ingredient it's allergic to, we can run the challenge test by testing each ingredient of its previous diet one at a time to determine which one causes the itching.

To do this, we identify the proteins in its usual diet by checking the ingredient list. Each week, we add one of those proteins to the elimination diet and watch for seven days to see if there's an adverse reaction. If the itching doesn't come back during this period, we rule out a food allergy to that particular protein.

For example, if our dog's usual kibble contains chicken and corn as ingredients, we could add small pieces of cooked chicken breast to the hydrolyzed kibble in the first week and see whether symptoms reappear. The following week, we'd mix the kibble with cooked corn and watch for an adverse reaction.

As you can see, fully diagnosing this condition takes time and patience, which is why many owners choose not to run the challenge test and simply keep feeding their pet a hydrolyzed or novel-protein kibble for life. Knowing which ingredient(s) our dog is allergic to lets us feed it any diet that doesn't contain those substances.