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Diseases That Commonly Affect Dogs: Allergies

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Whiskers, Paws and Love Inc. Team

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    Allergies are caused by an inappropriate immune reaction to allergens usually triggered by both the dog’s genetic make-up and the environment. His immune system determines that a harmless substance is dangerous, so his antibodies try to get rid of the foreign invaders as if they were a virus or bacteria. Part of the immune response is to release histamine, which disrupts the normal protective skin barrier and results in inflammation, causing redness and itchiness, especially on the face, paws, armpits, and lower belly. Because dogs tend to scratch and chew on those itchy spots, bacteria or yeast comes into contact with the irritated skin resulting in secondary infections, painful sores or “hot spots.” Allergies occur from exposure through the skin, through inhalation, and through direct skin contact; and rarely (in just 0.2 % of dogs) are they caused by an ingredient in his food. The list of potential environmental allergens is long. Many common allergens are found in the home; they include dust, dust mites, pollens (from trees, grasses, weeds), molds, dander, fabrics, feathers, medications, cleaning solutions, et cetera. Over the past ten years there has been a 30.7% increase in environmental allergy cases in dogs. The signs usually start when a dog is 1 to 5 years old. The most common food allergens are proteins, especially those from beef and chicken, but eggs, dairy, lamb, soy, corn, or wheat gluten can also cause allergic reactions. Each time your dog eats food containing these substances, the antibodies react with the antigens and symptoms occur. If your dog has a food allergy, it may be a reaction to just one ingredient, or several. And new food allergies can develop over time. Certain dogs can also be allergic to carbohydrates, preservatives, or food dyes. Although there is no cure for your dog’s allergies, the condition can be treated (meaning that it can be managed).


    The list of symptoms is long and frequently overlaps. Canine allergies generally don’t affect the respiratory system, but they are included here because they are a possibility. The list includes: red or itchy skin that flakes (especially on the paws, belly, groin, armpits, head, face, and ears), hair loss or bald patches, skin infections, chronic ear infections, head shaking, excessive licking and biting of the paws, hives, face rubbing, scooting their rear end on the floor, eye issues (red, itchy, puffy, or watery eyes or discharge), bumps, rashes (or swellings on the skin), skin wounds (referred to as “hot spots” and usually caused by persistent scratching), coughing or wheezing, sneezing or runny nose, diarrhea, vomiting (or other gastrointestinal symptoms), and the most serious - anaphylactic reaction, which may include facial swelling, sudden vomiting or diarrhea, difficulty breathing, collapse, and even death. Fortunately, it is uncommon for a dog to have an anaphylactic reaction due to seasonal, flea, or food allergies. If you ever notice anaphylactic symptoms in your dog - especially after a bee sting, vaccine, or new medication - bring your dog to a vet immediately!

    If any of the above symptoms occur often, you should suspect allergies. It is vital to find out the cause because different types of allergies require different treatments. Since food allergies are rare, other causes of skin conditions should be investigated first (but it is still important to consider them when trying to determine the cause of your dog’s allergies).Themaindifferences between environmental allergies and food allergies are that those caused by the environment may come and go with the seasons, while those caused by food can also cause gastrointestinal issues that include chronic gas, diarrhea, or vomiting. If your dog is itching only at certain times of the year, it’sprobably a seasonal allergy; but it’s important to remember that seasonal symptoms may worsen over time and become year-round.


    It is almost impossible for owners to determine what is causing your dog’s symptoms, so a vet visit is a necessity. Your vet will usually rule out other medical or emotional conditions that could cause similar symptoms first. Testing for other conditions is likely to start with a skin or ear swab/scrape to look for bacteria, yeast, mites, or other abnormalities. For example, microscopic skin mites cause skin symptoms that look like allergies (but some allergy treatments will make skin mites much worse); and an anxious or bored dog may lick or chew his skin. After that, blood work will probably need to be done (for example, to rule out a thyroid condition) as well as other diagnostic tests.

    There are two techniques for diagnosing environmental allergies in dogs: blood allergy testing and intradermal skin testing. Blood allergy testing means measuring antibody levels that your dog has formed against allergens in a sample of blood. The downside is that the results are not always accurate. Intradermal skin testing involves injecting a small amount of a pure allergen under the skin and measuring the allergic response. Dogs are typically sedated, and a section of their coat is shaved to monitor the injection sites for a reaction. Intradermal skin testing is the gold standard when it comes to diagnosing environmental allergies; however, it is not 100% reliable because it relies on subjective interpretation.

    A food trial is the best method to test for food allergies. This is a strict diet (for 1-3 months) that does not contain any ingredients your dog has eaten in the past - including treats, foods, or supplements. Randomly changing your dog’s diet can do more harm than good, and a true “hypoallergenic” diet can be obtained ONLY from a veterinarian, which is why food trials should be done under your veterinarian’s supervision.


    Your vet is likely to prescribe an anti-allergy medication and treatment for secondary skin infections with antibiotics, antifungals, and/or ear medications. Allergic responses like itching can be reduced with antihistamines, steroids, or other immune-modulating drugs. Fatty acid supplements may be helpful for mildly affected dogs or in conjunction with other treatments.

    Your vet may also suggest desensitization therapy for environmental allergies. These are weekly injections which are customized for your pet after allergy testing (oral administration of immunotherapy has become available recently). The downside of desensitization therapy is that it can take many months to work and up to half of the dogs treated will not see a significant change in their symptoms. However, it is worth trying for dogs with severe symptoms.

    Other ways you can help your dog who is suffering from an environmental allergy are: 

    • Avoid keeping your dog outside for too long when pollen counts are high
    • Wipe your dog’s paws and belly with a clean cloth or pet wipe after walks
    • Bathe your dog regularly with pet allergy shampoos, such as aloe and oatmeal, or with medicated shampoos (antibacterial and antifungal) and conditioners
    • Keep the home clean by dusting and vacuuming more thoroughly and changing air filters regularly
    • Clean your dog’s bedding more often
    • Give your dog skin and allergy supplements (omega fatty acids or probiotics)
    • Use vet-approved skin ointments or creams for flare ups
    • Use antihistamines such as Benadryl (check with your vet for which product to use and never buy products that also contain decongestants or other ingredients)

    Food allergies are typically addressed by changing your dog’s diet to limit the ingredients they consume. A limited ingredient diet might involve feeding them a protein your dog has never eaten before, such as rabbit or venison, and/or another carbohydrate source, such as green peas. Your dog must stay on a strict diet with a food that you know does not cause allergy symptoms. Sadly, that usually means common treats, table scraps, and even flavored medications are not allowed. Your vet can help you find alternative medications and a hypoallergenic diet that may be better tolerated. Changing your dog to a new type of food needs to be done gradually to minimize gastrointestinal distress. It can take up to three months for symptoms to resolve themselves after changing your dog’s diet.


    Contact allergies affect some dogs. An example of this might be when your dog has an allergy to your laundry detergent and develops a skin rash after lying on his freshly washed dog bed. Usually, the only parts of the body that will be affected are the parts that touched the allergen; and some pets may suffer from reactions to other inhaled substances like perfume or smoke. Anaphylactic reactions are possible from those types of allergies.

    Last but not least, you should consider food intolerance as a reason for your dog’s symptoms. Difficulty digesting or processing a certain ingredient may be the cause. Food intolerance is different from a true allergy because the immune system is not involved, so allergy treatments are unlikely to help.