Food allergies and intolerances in dogs: signs and what to do

Key points

• An allergy is an immune system reaction, almost always to a protein; an intolerance is a digestive problem that usually depends on the amount eaten.
• The most common signs are itching, paw licking, recurring ear infections and irregular digestion: vomiting, diarrhea, gas or soft stools.
• Introduce new foods one at a time, in small amounts, and watch for 3-4 days before adding another.
• The only reliable way to confirm a food allergy is an elimination diet of at least 8 weeks, designed and followed with your vet.
• Swelling of the face or lips, hives, trouble breathing or repeated vomiting are an emergency: go to the vet right away.

Food allergies in dogs and food intolerances are not the same thing, but they have one thing in common: they affect a particular dog, not every dog. Just as some people can't handle milk and others can't go near a peanut, some dogs eat chicken all their lives without a problem while others start scratching nonstop within a few weeks. A food being safe for dogs doesn't guarantee it agrees with yours.

In this guide we explain how to tell an allergy from an intolerance, which signs to watch for on the skin, in the ears and in digestion, how to introduce a new food without getting muddled, what to do if something doesn't agree with your dog, and why an elimination diet should always be done hand in hand with your vet.

Every dog is unique

At Recetas Caninas, no recipe contains ingredients that could harm a dog. But “safe” doesn't mean “perfect for everyone.” Chicken, beef, eggs, yogurt and whole wheat are healthy foods for most dogs, and yet they are among the ones that most often show up in food allergies, simply because they are what dogs eat most.

That's why it pays to look at your dog, not just the ingredient list: the state of their skin and ears, what their stools look like, whether they eat with appetite, how much energy they have. Your dog's “normal” is your best reference for noticing when something doesn't agree with them.

Allergy and intolerance are not the same

People use the words interchangeably, but they work differently, and that changes what you need to do.

	Food allergy	Food intolerance
What it is	The immune system reacts against a component of the food, almost always a protein.	The digestive system doesn't process a food well. The immune system isn't involved.
Typical examples	Beef, dairy, chicken, wheat, egg or soy proteins.	Lactose in milk, very fatty meals, too much fiber or a sudden change of diet.
Amount	A tiny amount is enough: one cookie or a few crumbs can keep the problem going.	Usually dose-dependent: a little is tolerated, a lot is not.
Main signs	Mostly skin and ears (itching, ear infections); sometimes digestive too.	Mostly digestive: gas, soft stools, diarrhea, vomiting.
When it appears	Usually with foods the dog has eaten before, sometimes for years.	It can appear the first time the dog eats it or when the amount goes up.

A clear example of intolerance is milk: many adult dogs digest lactose poorly, while plain yogurt or kefir, with far less lactose, agree with them in small amounts.

Signs that a food doesn't agree with your dog

On the skin and in the ears

• Itching that has nothing to do with the season: scratching, chewing or rubbing against the furniture.
• Constant paw licking, sometimes with the fur between the toes stained reddish brown by saliva.
• Red ears that are warm, smelly or full of dark wax, and ear infections that keep coming back even after treatment.
• Redness in the armpits, on the belly, the face or around the anus.

In digestion

• Vomiting.
• Diarrhea or soft stools on a regular basis, or more bowel movements a day than usual.
• Frequent gas and tummy rumbling.

In general

• Lethargy: less interest in playing or going for walks.
• Less appetite or, on the contrary, being frantic about food if they aren't absorbing what they eat well.

None of these signs is unique to food. Itching can be caused by fleas, mites or pollen; an ear infection, by the shape of the ears or moisture; diarrhea, by a parasite or something picked up on a walk. That's why it's best not to draw conclusions from a single episode.

How to introduce a new food

It's the best way to avoid scares and, if something does happen, to know what caused it.

1. One at a time. Never two new foods at once. If you try sardines and sweet potato for the first time on the same day and your dog gets an upset stomach, you won't know which one it was.
2. Little by little. On the first day, a small amount: a teaspoon for a small dog, a tablespoon for a large one, mixed into their usual food.
3. Watch for 3-4 days. If all goes well, you can gradually increase the amount. If it's a complete change of diet, spread it over 7-10 days, as we explain in how to switch from kibble to homemade food.
4. Look out for the signs in the previous section: skin, ears, stools and mood.
5. Write it down. A note on your phone with the date, the food and how it went saves you a lot of guesswork later on.

Day	What you do
1	A small amount of the new food, mixed into their usual meal.
2-4	The same amount or a little more, and nothing else new. Check stools, skin and ears.
5 onward	If all is well, increase the amount or start on another new food.

Keep in mind that an allergy can take longer to show. If your dog starts scratching weeks after a change of diet, don't rule out the food just because it went well at first.

What to do if signs appear

1. Remove the last new food and go back to what your dog ate before and tolerated well.
2. If there is mild diarrhea or vomiting in an adult dog that is still bright and alert, a bland diet for a few days usually helps; we explain it in what to feed a dog with diarrhea. Always keep fresh water available.
3. Write down what happened: what they ate, when, which signs and how long they lasted. If you can, take photos of the skin, ears or stools. That's far more useful to your vet than “I don't know what's wrong with him.”
4. Book a vet appointment if the signs last more than two or three days, come back every time your dog eats that food, the itching keeps them from resting, or the dog is a puppy, a senior or has another illness.
5. Don't give the food again “to see if that was it” without talking to your vet first.

The elimination diet, always with your vet

There is no blood, hair or saliva test that reliably diagnoses a food allergy in dogs. The test that works is an elimination diet: for at least 8 weeks the dog eats only one protein and one carbohydrate they have never eaten before, or a hydrolyzed prescription diet, and nothing else. If they improve, the previous foods are reintroduced one by one to see which one triggers the reaction.

It sounds simple, but it's easy to get wrong without realizing, which is why your vet needs to design it and follow it with you:

• The protein has to be truly new to your dog. Lamb or rabbit is new for many dogs, but not for all: these days they appear in plenty of kibbles and treats.
• Nothing else for weeks: no treats, no chews, no table scraps, no flavored toothpaste, no meat-flavored chewable medications. A single slip can undo weeks of effort.
• A homemade diet this limited is not complete: to keep it up for that long, your vet needs to adjust the amounts and choose a vitamin and mineral supplement with no proteins that could interfere.
• Itching can take several weeks to improve even when the diet is right. Giving up after three weeks often leads to the wrong conclusions.

Our single-protein recipes can serve as a starting point if your vet thinks they're suitable, but they don't replace their instructions.

Emergency signs

A severe allergic reaction is rare, but you need to recognize it. Go to your vet immediately, or to a 24-hour emergency vet if it's at night, if you see:

• Swelling of the face, lips, eyelids or muzzle.
• Hives or welts that suddenly appear on the body.
• Trouble breathing, unusual panting, or pale or bluish gums.
• Repeated vomiting, especially if they can't even keep water down, or bloody diarrhea.
• Sudden weakness or collapse.

Don't wait to see if it passes, and don't give human medications on your own: some antihistamines and anti-inflammatories you may have at home are dangerous for dogs.

Recipes for dogs with allergies or sensitive stomachs

If your vet has asked you to use a specific protein, or you simply want foods with few ingredients, these recipes are a good starting point:

• Hypoallergenic lamb and potato recipe: a single protein and a single carbohydrate.
• Homemade rabbit recipe for dogs with allergies: rabbit is a protein many dogs have never tried.
• Recipe for dogs with sensitive stomachs, for delicate digestion.

And to know which foods no dog should eat, allergies or not, go through the list of foods dogs should not eat.

Frequently asked questions

What are the most common food allergies in dogs?

The most common culprits are beef, dairy, chicken and wheat proteins, followed by egg, lamb and soy. It's not that these foods are bad: they are simply what dogs eat most, and allergies develop through repeated exposure. That's why a dog can become allergic to something they have eaten for years without any trouble.

How do I know if my dog has a food allergy?

Suspect it if your dog itches all year round, licks their paws a lot, has recurring ear infections or irregular digestion with no other clear cause. The same signs can come from fleas or environmental allergies, so the diagnosis is made by your vet with an elimination diet of at least 8 weeks followed by reintroducing foods.

Do blood, hair or saliva allergy tests work for dogs?

For food allergies, they aren't reliable. Blood tests give many false positives and negatives, and the hair or saliva tests sold online have no scientific basis. The gold standard is an elimination diet guided by your vet. Blood and skin tests can be useful for environmental allergies, such as dust mites or pollen.

How long does it take for a dog with food allergies to improve on a new diet?

Digestive signs usually improve within one or two weeks, but itching and skin problems can take six to eight weeks to clearly ease. That's why an elimination diet lasts at least 8 weeks, and it's important not to stop early or give anything outside the plan during that time.

How often can I introduce a new food to my dog?

The safe approach is one new food every 3-4 days, one at a time and starting with a small amount. That way, if gas, soft stools, itching or vomiting appear, you'll know which food caused it. If you're changing the whole diet, for example from kibble to homemade food, make the transition gradually over 7-10 days.