Common Signs of a Food Allergy in Pets

Golden retriever watching grey and white cat eat from food bowl

There is a wealth of information on the internet about pet nutrition, including articles about food allergies and so-called ‘hypoallergenic’ diets. You can even buy a test online to check for food allergies in your pets! Unfortunately, much of this has no scientific basis and is misleading. So here we unravel the truth about food allergies in pets.

What is a food allergy?

A food allergy happens when the body inappropriately reacts to food as if it were a threat, such as a bacteria or virus. This means the immune system mounts a response against it, causing a reaction. An allergic reaction can vary in severity, from causing mild diarrhea to a life-threatening anaphylactic reaction. Luckily, unlike allergies in humans, anaphylactic allergies in pets are rare.

A true food allergy is different from food intolerance. Food intolerance is also a reaction to certain foods, but it does not involve the immune system. While the symptoms are similar, they tend to be milder.

How common are food allergies in pets?

There is some controversy over this. Banfield Hospitals released a report in 2018 called State of Pet Health, where they analyzed data from many dogs and cats they had treated. They found that only 0.2% of dogs and 0.1% of cats were affected by food allergies.

However, other studies have reported higher figures. Some scientists believe it is rare, while others believe that many cases go undiagnosed, meaning it may be more common than we realize.

What are the symptoms of a food allergy in pets?

Symptoms of food allergies can vary. In dogs and cats, skin problems are the most common symptom of a food allergy. Itching, which persists and is not related to the seasons, is the main symptom. Other skin changes can include rashes, redness, pimples, scabbing, darker skin, thicker skin, and hair loss. Symptoms relating to the gut can be present too.

Symptoms of food allergies in pets include:

  • Itchy skin, which is not seasonal
  • Repeated skin infections
  • Smelly skin due to yeast infection
  • Changes to the skin and coat, including hair loss
  • Recurring ear infections
  • Diarrhea or soft stools
  • Straining to pass stools
  • Passing stools more often
  • Excess wind (burping and flatulence)
  • Sickness
  • Reduced appetite
  • Weight loss
  • Lack of energy or tiredness
  • Restlessness
  • Some other symptoms have also been reported but are very rare, such as seizures and asthma symptoms.

Cats with food allergies

Cats with food allergies can become generally itchy, or the itching may be concentrated around the head area (face, neck, and ears). Cats can also get diarrhea, and less commonly sickness, as a result of food allergies. They can develop lesions called ‘eosinophilic granuloma complex’ due to allergies of any kind, including food. These are plaques that appear as red, slightly raised, moist, and thickened skin. They are very itchy!

Dogs with food allergies

The itching tends to be generalized in dogs, with the feet, face, ears, and groin area being the worst affected. They often get itchy bottoms too. They may also suffer from gut issues, alongside skin complaints.

Of course, all of these symptoms can have other causes, some of them more severe than others. If your pet has these symptoms, then you should book an appointment with your veterinarian as soon as possible.

How can I tell if my pet is allergic to their food?

Food allergies can be hard to spot since the symptoms can be vague. They can start minutes or even days after your pet has eaten the food. A food allergy is a possibility if your dog or cat:

  • is up to date with their flea preventatives and is itching more than usual
  • develops skin rashes or skin changes
  • has hair loss
  • keeps needing treatment for ear infections
  • has red, itchy feet
  • has diarrhea
  • is unusually gassy

If you notice any of these in your pet, then you ought to consult your veterinarian. These issues can have many other causes, so food allergies need to be diagnosed by a clinician.

How are food allergies diagnosed?

Unfortunately, there is no easy test for diagnosing food allergies. There are tests available, such as blood tests and skin tests. There are even tests available online using a pet’s fur. However, none of these are reliable for diagnosing food allergies.

Ruling out more common causes

Before diagnosing food allergies, your veterinarian will want to rule out some other conditions. Such as flea allergies and mange, which can present with similar symptoms. This would usually involve skin scrapes, skin swabs, and using a prescription flea treatment.

Your veterinarian may also want to rule out underlying medical conditions that can cause skin changes, such as an underactive thyroid. They would do this using a blood test. They will also treat any problems that have happened as a result of the suspected allergy first, such as skin infections.

Elimination Diet Trial

If your veterinarian suspects a food allergy, they will perform an ‘elimination diet trial’ to confirm the diagnosis. Firstly, your veterinarian will ask you to feed a special diet for 8-12 weeks while keeping a diary of symptoms.

Homemade diets can be very effective since you are in complete control of the ingredients. However, they are very hard work and can be expensive. It can also be tough to ensure that they are nutritionally complete. Homemade diets should only be considered with the guidance of your veterinarian or a veterinary nutritionist.

Prescription diets are convenient and will be nutritionally complete. These often contain proteins that have been broken down into smaller parts or ‘hydrolyzed,’ so that the body cannot react to them.

Hypoallergenic Diets

It’s crucial not to use off-the-shelf ‘hypoallergenic’ diets. No diet can be hypoallergenic to all pets, as each pet will have different allergies. These diets often contain more than one protein or carbohydrate source. They are only hypoallergenic if your pet isn’t allergic to their sources, so they rarely work as an elimination diet.

There is also the possibility that they are cross-contaminated with other pet foods at the factory, meaning your dog or cat could react to the DNA in the diet that isn’t listed on the label.

Should I choose a hydrolyzed diet or a novel protein diet?

Your veterinarian will discuss all of the options with you so that you can choose which suits you and your pet. During this food trial, you must feed only the designated food. Treats, flavored toothpaste, flavored flea and worm preventatives, flavored medicines, and vitamin supplements can interfere with the trial. 

In some cases, even cross-contamination from shared water bowls or dogs eating the cat’s litter can ruin the trial. So, as hard as it is as a pet parent to be so strict, it is in your pet’s best interests to stick with the plan.

How will I know if the diet trial has worked?

If your pet’s symptoms have gone after the trial period has finished, then your veterinarian will instruct you to re-introduce their old food. This means the food they were eating when the symptoms started. This is known as re-challenging. If the symptoms recur within two weeks, then your veterinarian will confirm the diagnosis of food allergies. Next comes the detective work. 

How can I tell what food my pet is allergic to?

Common food allergies in dogs include beef, chicken, dairy, lamb, and wheat. Common allergies in cats include chicken, fish, dairy, and beef. It’s important to remember that each pet is unique, so these may not be the culprits for your pet.

Offering proteins

Your veterinarian will guide you through this next step. Following on from the ‘re-challenge,’ they will ask you to feed your pet the elimination diet again. Once the symptoms have passed again, they will advise you to offer one ingredient from your pet’s usual food (the one we now know they are allergic to), for example, chicken. 

After two weeks, if your pet shows symptoms, then your veterinarian will diagnose an allergy to that ingredient. This means you will need to exclude it from their diet going forward. If your pet is still fine, they will advise you on the next ingredient to trial. Once you have tested each ingredient, your veterinarian will discuss with you the best food for your pet long-term.

Allergies to several foods

Your pet may be allergic to more than one food. Once you find an ingredient they react to, it’s essential to follow your veterinarian’s instructions and complete the testing. 

Allergies to weeds, trees, and pollen

It is also possible that they have environmental allergies too, such as pollen or dust mites. This means your pet may improve on the trial but still have some symptoms. Your pet could need further tests or medicines to stop the itch.

Determining an allergy can seem like a lengthy and frustrating process. It is perfectly natural to feel frustrated at times! Please speak with your veterinarian if you are feeling this way or have any concerns. They are there to guide you through it and encourage you to the end.

How do you treat food allergies in pets?

The good news is that treating food allergies in pets is relatively easy. Removing all the identified food allergens from the diet is usually enough to resolve the symptoms. Food allergies tend to be life-long, meaning these exclusions need to be forever. 

Of course, flare-ups can happen if your pet accidentally eats the wrong food. So, further treatment during outbreaks may be necessary, such as antibiotics or antifungals for skin infections. It’s a good idea to feed pets with allergies separately to avoid accidents. If your dog is a scavenger, using a muzzle while on walks can help prevent accidents too.

Can a pet suddenly become allergic to their food?

Unfortunately, the answer is yes. It usually takes 2-3 months to become allergic to a food, but this can take much longer. So, the fact that your pet has had the same diet for a long time and been fine does not rule out food allergies as a possibility. 

‘But I haven’t changed his diet recently?’ is a common query in the vet’s office when we discuss food allergies, but allergies can develop to the food they’ve had all their life.

Can pets develop allergies later in life?

Some studies show that around a third of dogs with food allergies develop them before they are one year old, with most being diagnosed by five years of age. Cats tend to develop food allergies slightly later, between two and six years old. However, food allergies can develop at any time. They have been reported in animals from less than six months up to 15 years old.


If you think that your pet may have a food allergy, call your veterinarian for an appointment. Food allergies can be frustrating and time-consuming to diagnose. However, once the process is over, the treatment is easy, cheap, and effective. 

Following the tests to the end can avoid your pet needing medication and multiple veterinary visits in the future. Your veterinary team is there to support you all the way.