Allergies in Pets: Diagnosis and Management

Do your pets have trouble with itchy skin? Ever noticed your dog chewing at his feet? How about infected ears or inflamed skin, or even diarrhea? These can all be manifestations of allergies in dogs and cats. Allergies in pets are a common problem, and it can be complicated and frustrating to figure out what works. The very first tool you need to fix your pet’s allergies is a good understanding of the problem. Let’s begin…

Food or Environment?

There are two main categories of allergies. An animal (or person) may be allergic to food, or to environmental factors such as pollen, dust mites, or mold. Certainly they may be allergic to both categories, but we are often able to narrow it down to just one. In the northeast, among dogs with clinical signs of allergies, about 85% have
environmental allergies and only 15% have food allergies. Food allergies are much more common in cats; about 40- 50% of cats with clinical signs of allergy have a food allergy.

Diagnosing & Treating Food Allergies

Determining if an animal has a food allergy is more complicated than many owners expect. “But I changed his diet, it didn’t help!” many owners exclaim. If you changed the brand of food but both types included chicken as an ingredient, and your dog happens to be allergic to chicken, of course it didn’t help. You’d have no way of knowing that chicken was the problem food, either. That is the type of information that is needed, and the way to find out is by doing a food trial. While blood tests for allergies exist, the blood test results for food allergies are generally not very accurate. Instead, we demonstrate that a specific ingredient is a problem by excluding it from the diet and looking for an improvement in allergy symptoms. If the food is then reintroduced, symptoms will return.

Food allergies are to a specific protein ingredient in the food: chicken, beef, lamb, fish, egg, whey, rice, soy, wheat, corn, barley, etc. (notice it is NOT just the grains we are blaming!). No need to worry about the vitamin and mineral supplements (with names like “calcium iodate” or “niacin”) that also appear on the ingredient list – they are not at fault.

Here are the steps to follow for a successful food trial with results that can be trusted:

Find a new diet that does not include ANY of the same major ingredients as what you are currently feeding, or have fed in the past. This requires you to read the whole ingredient list on the back of the bags, not just the description of the diet on the front of the bag (a diet called “Lamb and Rice Sensitive Skin” surely includes many more ingredients than just lamb and rice). You may be able to find a kibble that works, or you may have an easier time preparing a home cooked limited ingredient diet. This can get complicated, we know, and we don’t expect you to figure it out on your own. If you’re uncertain of how to proceed, don’t guess – talk to your veterinarian.
Eliminate any other foods you are currently feeding, as these may also contain the allergen at fault. This means NO TREATS, NO TABLE FOOD, no rawhides or marrow bones, and no flavored medications (such as Heartgard or Rimadyl). “No treats!? But Barkey will be so sad!!” Barkley will also be sad if we don’t get his allergies under control… But fortunately, if you follow the same rules for choosing a new diet, you can find an appropriate treat to offer. For example, if Barley’s previous diet did not include duck as an ingredient, you can safely use a freeze-dried duck liver treat. If he has never had carrots before, you can offer this as a treat. Several of the limited-ingredient diets aimed at allergy management also make a treat to “match” the diet, so this may be an option as well. And for the flavored medications we need to exclude, your veterinarian can help you find safe alternatives to use during the food trial.
Continue this new limited-ingredient diet for 8 weeks, and watch for an improvement. If you do not see an improvement and are certain you did everything right, the problem is not a food allergy. It’s as simple as that.
Continue the limited-ingredient diet, or try adding in other ingredients one at a time and watch for a reaction. You can continue the limited-ingredient diet forever if it is practical to do. If you are using a home-cooked diet, though, you will need to make sure it is nutritionally complete before we decide to continue it forever – your veterinarian may suggest you contact a university nutrition service to get it exactly right.

Diagnosing & Treating Environmental Allergies

Sometimes it is important to determine exactly what in a pet’s environment they are allergic to, while at other times it is not going to change what we do to make things better. For example, you can potentially control allergies to any sort of pollen or mold just by giving a daily antihistamine. On the other hand, if the dog’s allergies are caused by flea bites, of course you need to discover the dog’s flea problem so you can get rid of it and not rely on daily medication. Here are the general steps we take to treat environmental allergies WITHOUT a specific diagnosis.

Remove the allergen, if possible. Check for fleas, and if found, get rid of them for good. Is pollen the problem? Giving your pet a bath regularly (perhaps weekly) during allergy season will physically remove it from their fur. Any shampoo will clean away allergens, but your pet may benefit even more from a medicated shampoo that also treats yeast or bacteria causing irritation to the skin.
Address any infection of the skin that has developed as a result of allergies. Ear infections and skin that has developed “hot spots” or has become raw, inflamed, and infected from scratching need to be addressed, usually with an oral antibiotic and a steroid. It is ideal to avoid using a steroid long-term, but your pet may need to rely on one initially to reduce severe inflammation.
Try giving a daily antihistamine and/or fish oil supplement.. Antihistamines work best when they are given daily as a PREVENTATIVE, rather than as a response to an allergy flare-up. Allergy medications sold for human use (such as Benedryl or Zyrtec) are generally safe for pets, but please talk to your vet about the best kind and appropriate dose for your pet. Some can be given once daily, others require higher or more frequent doses for pets than people. NEVER give an antihistamine that also contains a decongestant or anti-inflammatory ingredient to your pet. Generics, however, are less expensive and no less effective than the corresponding brand name drug. Fish oil has the potential to reduce inflammation and moisturize the skin, but remember, if fish is on our list of foods to avoid, a fish oil supplement is not an option.
Consider an immune-modulating medication. In some cases, allergies are so problematic for an animal that your vet must consider a drug using a drug that alters how the immune system works. Granted, the immune system is important to prevent infectious disease and we’d rather not mess with it! Fortunately, newer drugs are better targeted to controlling allergies while leaving other aspects of immune function nearer to normal. Your vet may discuss these types of drugs with you if the need arises.
Consider allergy testing and immunotherapy (allergy shots). This is the most advanced and most specific tool we have against allergies in pets. It gives is the opportunity to “re-teach” the immune system to ignore allergens while leaving its disease-fighting function completely intact. Remember, allergy testing is useful against environmental allergies, NOT food allergies. We hope you’ll consider this approach as your best option for a pet with severe environmental allergies that cannot be adequately controlled by antihistamines or reducing allergen exposure.

Allergies in pets are a complex problem, and regardless of the cause, it can take some persistence to find the best solution. This article is meant to set you off on the right path, and your veterinarian is ready to guide you along the way.

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Copyright Bolton Veterinary Hospital / Michelle K Pesce, DVM

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