Food allergies in dogs and cats: signs, triggers and the elimination diet

An itchy dog, a cat that keeps vomiting, a new rescue whose history you don't know: "does my pet have a food allergy?" is one of the most common questions owners ask. Food allergies are real, but they're less common than marketing suggests, and the only reliable way to find one is a proper elimination diet. Here's how that works.

Signs of a food allergy or intolerance

• Skin: itching year-round (not just in pollen season), especially the face, paws, ears and rear end; repeat ear or skin infections.
• Gut: vomiting, diarrhea, soft stools or more frequent bowel movements.

The same signs have many other causes, including fleas, environmental allergies and infections, so see your vet before changing foods.

The most common food allergens

A 2016 review of published studies by veterinary dermatologists Mueller, Olivry and Prélaud counted which foods caused reactions in pets with confirmed food allergies:

The pattern mostly reflects what pets eat most. Animal proteins top the list, and wheat is the only grain near the top for dogs, which is one reason grain-free food isn't a fix for most allergies. See grain-free dog food and DCM.

How vets diagnose it: the elimination diet

1. Pick a diet your pet hasn't eaten before. Usually a prescription hydrolyzed diet (proteins broken down so the immune system doesn't react) or a novel-protein diet. A home-cooked diet can work if a veterinary nutritionist formulates it.
2. Feed only that, strictly, for 8 weeks. About 80% of food-allergic pets improve within 5 weeks (dogs) or 6 weeks (cats), and 8 weeks catches more than 90%.
3. Re-challenge. If signs improve, your vet has you feed the old food again. A flare within days (usually within a week) confirms it. Then you can add single ingredients back one at a time to find the trigger.

Common mistakes that ruin the trial

• Treats, rawhide, flavored toothpaste or supplements.
• Flavored chewable medicines, including some monthly parasite preventives. Ask your vet for unflavored options.
• "Just a little" peanut butter, cheese or a pill pocket.
• Another pet's food bowl in a multi-pet home.
• Over-the-counter "limited ingredient" foods. In one study of 29 such dog foods, 65% contained undeclared chicken DNA and 41% contained undeclared pork.

Skip the allergy tests

Blood, saliva and hair tests for food allergies aren't reliable and can point you at the wrong foods, according to veterinary dermatologists. The elimination diet is still the standard.

After the diagnosis

Once you know the trigger, many pets can move to a regular complete and balanced food without it. Read the ingredient list, not just the front of the bag: a "salmon" food may still contain chicken fat or chicken meal. Our label guide explains the naming rules, and our food grades show recall records and the maker's nutrition standards.

Not veterinary advice. Work with your vet on any elimination diet; cats in particular can become seriously ill if they stop eating.

Questions