The 5 Myths of Food Allergies

In cats and dogs, like us humans, food allergies are on the rise.  Discovery a pet’s long-standing skin, ear, or gastrointestinal problem is due to a single dietary factor, rather than invisible pollen or mystery contact irritant, is often a revelation for a frustrated owner.  During my career, I have received more ecstatic gratitude for recommending an elimination diet, than for any other dermatologic intervention. Fingering an offending ingredient empowers pet owner with an opportunity to take control of their pet’s skin problem, and walk away from the endless treadmill of cortisones, antibiotics and ointments.  The biggest barriers to an owner making this breakthrough are several food allergy myths. Let’s get them cleared up, once and for all.


Commerical foods can contain a Noah’s Ark of species

Myth 1.  Food allergies only cause gastrointestinal symptoms

Sure, weight loss, diarrhoea and vomiting can result from food allergy, but so can skin, ear, and paw problems.

In dogs, there’s no classic set of symptoms, but non-seasonal itchiness or repeated infections, affecting groin, paws, ears and face should raise suspicion. In one study, 30% of dogs with food allergy had ear problems alone.

Given these symptoms can be caused by many other types of more common allergies, such as inhalant (pollens, fungal spores, dust mite etc) and contact (plants, synthetic chemicals), the rushed local vet will sometimes just use a medical remedy (cortisones, antibiotics, cyclosporine) rather than bother with a time-consuming description of an elimination diet, which may only offer a 5% chance of success.

In cats, there’s a more explosive and easily recognisable pattern, that’s often picked-up on first presentation. Often misread by owner as catfight wounds, any sudden outbreak of intense itching of face or neck, scratched raw and scabbing, should prompt an elimination diet. Thinning of the coat or crusting dermatitis anywhere on the body may also be food allergy related.


Myth 2:My pet’s recent skin or tummy trouble can’t be caused by food allergy, as he’s been eating the same food for years without a problem

For vets, convincing pet-owners a new problem could be due to a long-consumed, dietary ingredient is a weekly challenge.

Allergies are diseases of exposure. The more your immune system encounters a potential allergen, the more likely it will develop an allergy to it: surgeons become allergic to latex, gardeners develop allergies to insect bites, and milk drinkers become reactive to lactose. Genetic predisposition plays a part but, more importantly, each time your body reacts to a allergen, be it bee sting, peanuts, or penicillin, it can sensitise the immune system further. Unless steps are taken, avoidance or desensitisation, repeated exposure will often result in progressively worsening allergy.

So, the more addicted a cat or dog to particular food, especially if eaten year-in, year-out, the more likely it contains the allergen. This process of sensitisation can delay the onset of food allergies until middle or later life, however food allergy  can also strike the very young, from 2 months of age.

If looking for a diet least likely to cause an allergic reaction, choose ingredients the patient has rarely, if ever, eaten.


Myth 3: Animals with food allergy will suffer symptoms all year round

Given the symptoms of food allergy persist while an allergen is fed, you would expect the problem to be continuous, all year round.  In reality, it is common to see some variability in intensity of symptoms throughout the year.  An obvious explanation for this is variations in diet, however there are others.

Animals suffering multiple allergies will have superimposed symptoms. A food allergic dog, who also reacts to inhaled pollens, may have mild, food-related ear problems all year round, which only reach sufficient severity in spring for owner to notice.   When controlling airborne pollens is out of the question, testing for contributory food allergens may offer a simple management strategy that reduces severity of a seasonal allergy.

Similarly, the waxing and waning of superimposed secondary fungal and/or bacterial infections, which may be more prevalent during the warmth and humidity of summer, may leave both pet owner and vet with the impression a continuous problem is intermittent or seasonal.


Myth 4: Preservatives and colourings are the most common food allergens

It’s easy to demonise man-made additives, and it’s true these occasionally cause food allergy, but far more commonly the offending ingredient is something more fundamental. Protein is the most common, and given beef and fish are the most common protein sources, it should be no surprise they are your top 2 allergens in dog and cat. Others include, lamb, chicken, dairy, egg, soy, or carbohydrate, such as wheat or corn.

These allergens make up the bulk of ingredients in most commercial foods, so switching brands or flavours is unlikely to give you a good result. What’s more, switching to a home made diet, which eliminates preservatives and colourings but includes beef, or any protein the pet has eaten frequently, is likely to result in failure.

Even using an expensive commercial diet, specifically formulated for food allergic pets and recommended by your vet, may fail to demonstrate an improvement if you’re unlucky enough to select one that has the rare ingredient to which your pet is allergic.


Myth 5: Flavour of pet food, as stated on packaging, describes actual ingredients

Despite the earnest attempts by pet food manufacturers to accurately list ingredients, it’s often difficult for them, or vets and pet owners, to be certain what allergens may be lurking in kibble or tins.  The now ubiquitous warning ‘may contain traces of egg, nuts and soy’ should have already alerted you to the fact that industrial food manufacturing, for man and animal, is not coping well with food allergens.

In reality, much commercial food is a Noah’s ark of protein sources.  If you think your cat may be food allergic, switching from beef and fish flavours, to turkey and lamb, may see an improvement but ongoing itching could be beef contamination.

Commercial pet foods vary markedly in quality and it’s probably true: the more you pay for a premium diet, the greater the confidence in it’s claims. There’s only a handful of commercial foods vets recommend for an elimination diet, usually based on novel proteins (kangaroo, rabbit, duck, venison) or hydrolyzed, non-allergenic protein (Hills z/d, Royal Canin Hypoallergenic HP), but most vet dermatologists admit: a home made, novel protein diet is the only way to be absolutely sure of a good response to elimination diet in the food allergic patient.


  • If you have a pet with any repeated skin problems, even if they seem seasonal, try a proper elimination diet at least once in your dog’s life time. Simply excluding a protein may free you from the treadmill of vet visits, cortisones and other drugs. If it fails to improve the skin, ear or tummy problem, you can refute the vet’s suggestion of a food allergen forever more. If it works, you’ll be thanking me.
  • If you’re doing an elimination diet, do it properly. If your pet has food allergy, and you get the elimination diet wrong, you’ll be tricked into believing  diet offers no hope and cursed with years of chronic allergy.  For 10 years I stoically endured uncontrolled food allergy, misdiagnosed as IBS based on an equivocal biopsy result and no response to a poorly designed food elimination trial. Allergies to common ingredients demand rigorous adherence to a diet for at least 6-8 weeks and may temporarily exclude bones, treats, and flavoured medications.
  • Don’t assume changing brands, or investing time in the most organic and nutritious of home cooked diets, will necessarily get rid of an allergen. Focus on using weird ingredients like potatoes, rice, kangaroo or rabbit. Fish-based diets are a good choice for dogs, as they’re usually loaded with Omega-3’s, but not for cats.

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2 Responses to “The 5 Myths of Food Allergies”

  1. Abram Rotella says:

    What’s Up! Just wanted to leave a comment. I truly was impressed by your post

  2. Lin says:

    I just wanted to add that with cats especially you have to be prepared for them trying to steal forbidden food left, right and centre! We’ve been feeding our allergic cat on expensive rabbit for a few weeks, only to discover she’s been helping herself to dry food from the dog’s food bowl and if we turn our backs, she is on the bench licking plates or pans and trying to grab food out of containers. So I cannot trust the results until we learn to be more strict and make sure she cannot snack on the side! Which is harder than it seems because our kitchen has no doors… But we’ll persist.

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