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What Happens

Food allergies in pets work just like they do in humans. Your cat or dog’s immune system mistakes an ingredient in their food as something harmful. Their body shifts into defense mode, which causes allergy symptoms to start. Your pet might have red skin or itchy ears. They could start to have an upset stomach or diarrhea. Cats are also likely to get small, fluid-filled bumps, often around their head and neck.

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Any Pet Can Have an Allergy

The exact number of dogs and cats who have a food allergy isn’t known. Labrador retrievers, cocker spaniels, and West Highland terriers may be the breeds most at risk. In cats, Siamese and Siamese crosses are more prone to this type of allergy than other breeds. Your pet isn’t just born with this problem, though. They may eat the same type of food for up to 2 years before an allergy starts and they begin to show symptoms.

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Foods Most Likely to Cause a Flare

Animal proteins are the most common cause of food allergies in pets. That includes chicken, beef, dairy, and egg. And despite how much your cat may love tuna, fish is known to cause a food allergy, too. Symptoms in some pets may even come from a plant-based ingredient, although that’s rare.

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How to Find the Trigger

The best way to find out what’s going on with your pet? A “diet challenge.” For 10-12 weeks, you’ll feed them only special food from your vet. You’ll also take away all treats, flavored toys, and even pet toothpaste. If your pet has a true food allergy, their symptoms will improve, then worsen once you return to the old diet. You could see a flare-up as soon as an hour or up to 2  weeks after they eat.

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Pinpoint the Problem

You’ll need to do this diet trial one more time to figure out which part of your pet’s food is the culprit. That can be tough to do. Many types of dog and cat food contain more items than what’s listed on the label. To find the exact allergy source, put your pet back on a controlled diet until their symptoms improve again. (This often takes less than 2 weeks.) Then, add back a single food item at a time and watch for signs of an allergy.

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Take Extra Care With Cats

It can be tricky to put your cat through a diet trial. Felines are famous for being picky eaters and don’t like to change foods. If your cat doesn’t eat for more than a day or two, they could be at risk for a disease called “hepatic lipidosis.” This happens when their liver gets backed up with fats. In severe cases, it can be fatal. If your cat loses weight, lacks energy, is throwing up or has diarrhea, call your vet right away.

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How (Not) to Test

Some food allergy test kits promise to use your pet’s hair or spit to pinpoint which allergy they have. While that seems a lot simpler and faster than putting your pet through a diet challenge, there’s no proof the results will be correct. One study tested a kit on fur from a stuffed animal instead of a real dog. The results showed that even this fake pet had food allergies!

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Watch Your Pet Like a Hawk

Once you know the food that sets off your pet’s symptoms, avoid it as much as you can. And keep in mind, your pet could have an allergy to more than one thing. In one study, 10% of dogs that were tested had a food allergy to five different items. Your pet could also have a “cross-reaction.” For instance, if they have an allergy to beef, a different food from that same animal, like cow’s milk, might also trigger their symptoms.

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Support With a Special Diet

Some companies make special food for allergy-prone pets that you can buy at your vet’s office. It’s made with extra care to weed out common allergens. Many brands also contain what’s called “hydrolyzed” protein. These are proteins broken down into such tiny pieces that your pet’s immune system won’t notice or react to them. Does your pet really need them? Ask your vet.

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Pros and Cons of Homemade Food

Of course, you can make your pet’s food from scratch. That’s a good way to ensure what they eat won’t set off their symptoms. But do some research first. Not all recipes provide the right nutrients your dog or cat needs to stay healthy. (And if you choose a raw food diet, you risk feeding your pet harmful germs.) Consult your vet or an expert in pet nutrition so you don’t trade your pet’s allergy for a larger health problem.

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Does Going Gluten-Free Help?

Gluten is a protein found in grains like wheat, rye, and barley. Some people are very sensitive to it, but they aren’t always allergic to it -- and this isn’t a common problem in pets. Cats aren’t known to have problems with gluten. In dogs, problems with gluten have only been found in Irish setters and perhaps border terriers.

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What Else Could It Be?

Even if your pet doesn’t have a food allergy, they may have a “food intolerance.” The amount of food they eat, how it’s cooked, or the fiber in it could cause symptoms. Your pet may also have a digestive or skin issue that needs to be treated. An allergy to something besides food, such as flea or insect bites, dust mites, pollen, or mold could also be to blame. Your vet can help you figure out what’s ailing your pet and get them feeling better.

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Sources | Medically Reviewed on 09/02/2020 Reviewed by Amy Flowers, DVM on September 02, 2020


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Cummings Veterinary Medical Center at Tufts University: “What every pet owner should know about food allergies,” “Feeding the homemade diet.”

Cornell Feline Health Center: “Food Allergies.” Veterinary Medical Center at Tufts University: “Chance Are It’s Not a Food Allergy for Your Dog.”

Pet Food Institute: “Food Allergies.”

Merck Veterinary Manual: “Overview of Food Allergy,” “Feline Hepatic Lipidosis.”

Louisiana State University Veterinary Teaching Hospital: “Food Allergy: Canine Food Allergy.”

Journal of Feline Medicine and Surgery: “Food Allergy in the Cat: Diagnosis by Elimination.”

Critical Reviews in Food Science and Nutrition: “Food Allergy in Dogs and Cats: A Review.”

American College of Allergy, Asthma, and Immunology: “Wheat Allergy.”

Gut: “Dietary modulation of gluten sensitivity in a naturally occurring enteropathy of Irish setter dogs.”

8th World Congress of Veterinary Dermatology, Bordeaux, France 2017: “Inaccuracy of Hair and Saliva Test in for Allergies in Dogs.”

Reviewed by Amy Flowers, DVM on September 02, 2020

This tool does not provide medical advice. See additional information.

THIS TOOL DOES NOT PROVIDE VETERINARY ADVICE. It is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional veterinary advice, diagnosis or treatment and should not be relied on to make decisions about your pet’s health. Never ignore professional veterinary advice in seeking treatment because of something you have read on the WebMD Site. If you think your pet may have a veterinary emergency, immediately call your veterinarian.