The Itchy Dog: Nutritional Management of Canine Allergic Dermatitis

Is there anything worse than watching your furry friend itch themselves raw? As a human who has suffered from allergic dermatitis, I can tell you that in my opinion that when it is severe, there is not much worse. There have been times that I couldn’t even think of anything other than itching until I had no skin left. So, let’s discuss the ways to help prevent our pets from suffering the same fate.

The first things to consider are the underlying causes of allergic dermatitis. The main causes are contact allergies, insect allergies, environmental allergies, or food allergies. Contact allergies arise from skin contact with an allergen. Although this is rare in dogs, the irritant could be something like a laundry detergent that was used on the dog’s bed, a floor cleaner that they laid on, or a shampoo or topical spray. Environmental allergies can be seasonal or non-seasonal and could be due to a reaction from tree pollen, grasses, dander, dust, or food storage mites. When we talk about environmental allergies which result in allergic dermatitis, we call it atopic dermatitis. Examples of insect-related allergic dermatitis could be a flea bite allergy or even an allergic reaction to a fly bite. Food allergic dermatitis occurs when a food allergen induces an immune-mediated reaction in the body. This typically occurs after the dog has been exposed to the allergen, usually protein, over time (years) and the most typical complaint is itching. Food allergies are non-seasonal and in 20-30% of the cases, there is another concurrent allergy such as flea allergic dermatitis, or atopy.¹

Identifying the cause

The first step to management is identifying the underlying cause. Contact allergies typically have an obvious pattern where the skin that touched the offending substance is only affected, or there was a known recent exposure such as trying out a new shampoo.

Environmental allergies can be tested for with a blood test or a skin test. Insect-related allergies can be identified by the type of lesion, known exposure, or visualizing the tiny offenders. However, this can be easier said than done. For example, with flea bite allergies it only takes one bite for the dog or cat to become insanely itchy so even if there is not a flea infestation, a flea bite allergy can still occur. In addition, people with poor eyesight sometimes overlook obvious flea infestations which are visible to others. This happened enough in practice, that I swore I should keep reading glasses in my lab coat just so some owners could see the fleas I would pull off their pets as they insisted their pet could not have fleas since it was primarily or fully in the house. Those little buggers can get inside!

Food allergies can only reliably be diagnosed with an elimination food trial which results in the resolution of allergic signs, followed by the reintroduction of the problem food and a return of the allergic signs. Final confirmation comes from the re-resolution of allergy with the reintroduction of the elimination food. Determining which food(s) is(are) the specific problem requires testing individually to see the allergic response. Although blood tests do exist for food allergies as well, they are woefully inaccurate.^2-4

Nutritional Management of Allergic Dermatitis

Food allergies are both identified and treated with an elimination diet trial. This diet trial will hopefully eliminate all potential allergens which would resolve the itching and skin irritation allowing us to identify food as the cause. These diet trials use either a novel diet or a hydrolyzed diet.

Novel diets use one protein source and one carbohydrate source which the pet has hopefully not been exposed to in the past therefore, the body won’t recognize the proteins in the carbohydrate or protein source as an allergen and will not mount an allergic response. Alternatively, a hydrolyzed diet can be used. These diets use a protein source that has previously been enzymatically broken down into short amino acid chains which the body shouldn’t be able to recognize as an allergen. Since these are short amino acid chains and no longer recognized as an allergen the initial protein source could theoretically be anything. For instance, even if a dog has a chicken allergy, a hydrolyzed chicken diet could be used to manage the allergy because the hydrolyzed chicken is no longer identified by the body as chicken. Hydrolyzed diets also typically use a novel carbohydrate source but only the starch portion which should be devoid of protein and again, not mount an allergic response.

These diets often use other supporting ingredients and nutrients to help repair the skin barrier and reduce skin inflammation. Important fatty acid such as linoleic acid is needed to help maintain skin cell health as well as the anti-inflammatory omega-3 fatty acids EPA and DHA which come from marine sources. Since these fats should be free of protein, the source should not induce an allergic response from the pet.

These diets should be used alone (no treats, table foods, flavored medications, etc.) for up to 12 weeks to identify if a food allergy is the cause of the pet’s itching. Thereafter assuming resolution, many pet owners choose to keep their pets on this hypoallergenic diet rather than attempting a switch back to a typical maintenance diet and risking the recurrence of the itching. However, if identifying the inciting cause is desired, trials with the reintroduction of alternative ingredients need to be performed.

Although environmental allergies cannot be treated with diet alone, there are diets that help support skin health and can help to reduce skin irritation, itching, lesions, and the use of medications, in atopic dogs. These diets also use fish or algae oils to provide EPA and DHA as well as provide sufficient linoleic acid to support skin health. Some diets also contain bioactive ingredients and phytonutrients to help support skin health and reduce itching. Studies have shown that when dogs with atopic dermatitis are fed this type of diet, they have significant improvement over time. For instance, one study's diet which contained turmeric extract and licorice extract as well as high vitamin E and lutein supplementation resulted in significantly reduced itching after 3 months.⁵

In general, assuming there are ongoing discomfort or skin lesions having an environmental allergy test performed for your pet and then managing with diet will help to improve the dog or cat’s comfort or can completely resolve the issue. This is great because no pet should have to live with allergic dermatitis.

References

1. Verilinden, A. Hesta, M. Millet S., Janssens GPJ. 2006. Food allergy in dogs and cats: a review. Crit Rev Food Nutr. 46(3):259-73.
2. Mueller RS, Olivry T. 2017. Critically appraised topic on adverse food reactions of companion animals (4): can we diagnose adverse food reactions in dogs and cats with in vivo or in vitro tests? BMC Vet. Res. 13:275.
3. Vovk LU, Watson A, Dodds WJ, et al. 2019. Testing for food-specific antibodies in saliva and blood of food allergic and healthy dogs. Vet. J. 245:1-6.
4. Bernstein JA, Tater K, Bicalho RC, Rishniw M. 2019. Hair and saliva analysis fails to accurately identify atopic dogs or differentiate real and fake samples. Vet .Dermatol. DOI: 10.1111/vde.12716.
5. Watson, A. Rostaher, A. Fischer, NM. Favrot, C. 2022. A novel therapeutic diet can significantly reduce the medication score and pruritus of dogs with atopic dermatitis during a nine-month controlled study. Vet. Dermatol. 33(1):55-e18

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About the Author

Renee Streeter is a Doctor of Veterinary Medicine and a Diplomate of the American College of Veterinary Internal Medicine (Nutrition). She obtained her Bachelor's degree in Animal Science from Cornell University and served as a farm animal nutritionist for a major feed company before attending veterinary school at Ross University. Her clinical rotations were done at Cornell University’s college of veterinary medicine, where she stayed on to do her Clinical Nutrition residency. While working in a large general practice and doing clinical nutrition consultation, Dr. Streeter also founded her own veterinary nutrition consulting company and currently helps industry clients through her position as the Nutrition Practice Principal at BSM Partners.