Dog: Food Allergy

General information

An allergy is an abnormal reaction of the body to an allergen which is a substance that triggers the allergic reaction. An allergic reaction is a hypersensitivity response occurring when the body’s immune system overreacts to the substance. Unlike people, dogs rarely have respiratory allergies but instead exhibit allergic symptoms as skin or gastrointestinal conditions. A food allergy is an allergic reaction to any substance being fed.


The exact cause of a food allergy is unknown. However, the ingredients most commonly responsible for food allergies are beef, chicken, pork, eggs, milk and diets high in protein. Corn and wheat have also been implemented. Ingredients such as preservatives or dyes are also potential allergens.

Food allergy can start at any age and a change in diet is not necessary for the development. In fact, most affected dogs develop an allergy to a food that they have been fed for a long time. Dogs with atopic dermatitis or flea allergy may have an increased risk for developing a food allergy.

Cardinal symptom



Dogs with food allergy will usually lick, chew, bite or scratch at their feet, muzzle and axillary (armpits). Otitis or inflammation of the ear can occur. As the dermatitis progresses, the entire body may be affected. Other signs include hair loss and red, inflamed skin from self-trauma due to scratching. Dogs can develop a secondary infection due to bacteria (pyoderma) or yeast (Malassezia) resulting in raised papules, pustules and scabbing which further worsens the pruritis (itching). In chronic cases, the skin may become thickened, pigmented and develop a foul odor. Although less common, dogs with food allergy may also develop diarrhea and vomiting.


Diagnosis of food allergy is made from the history, clinical signs, exclusion of other pruritic conditions and a positive response to a food trial. Dogs with food allergy may also suffer from flea allergy dermatitis. Because of this, it is important that any itching dog be carefully examined for signs of flea infestation. A skin scraping should also be performed to rule out ectoparasites such as Sarcoptic mange, Dermodicosis and Cheyletiellosis. Dogs with food allergies tend to not response to corticosteroids and their itchiness is not a seasonal problem.

A food trial involves feeding a diet which has only one source of a new or novel protein and carbohydrate. This diet should be fed for 8 to 12 weeks and the dog watched closely for signs of food allergy. When on a food trial, it is imperative that the dog eats only the trial diet-no treats, no flavored toys, no chewable medications, no human food. A homemade diet can be fed but many pet food companies now offer diets that are additive and preservative free with unusual protein and carbohydrate sources. Good examples of novel diets include venison and potato, fish and potato, duck and pea and kangaroo and potato. Lamb and rice diets were once touted as being hypoallergenic; however, these are no longer thought to be beneficial for food allergy dogs. Most dogs begin to respond (by becoming less itchy) to the food trial by six weeks although some dogs take longer.

To confirm a food allergy, it is necessary to reintroduce the dog’s original diet to see if the allergic reaction returns. Itching usually resumes within 14 days if food allergy is the reason for the itchy skin. It is possible to identify specific offending foods by adding a single source of protein or carbohydrate to the test diet such as cooked chicken or wheat flour or adding a commercial diet. If no itching results after two weeks, the dog is not allergic to that specific component or diet.


Treatment of a food allergy is to avoid feeding foods that cause itching. About 80% of food allergy dogs can be managed with commercial diets. When avoidance is not feasible, corticosteroids and antihistamines may be used to control itching although these medications are less effective for food allergy dogs.


The prognosis is good for resolution of clinical signs in dogs with food allergy providing the dog is strictly maintained on acceptable foods. Deviation from these foods will result in a relapse of clinical signs.


Many dogs with food allergy are also allergic to fleas and inhalants. These dogs are much more sensitive to even a small increase in the amount of allergen. The allergic threshold is the amount or level of allergens at which a dog will show clinical signs of allergies. The lower the allergic threshold, the more sensitive the dog. It is extremely difficult to eliminate all the allergens in a dog’s environment. However, in order to provide relief for your dog, you do not need to eliminate them all. Rather, you only need to prevent the allergens from exceeding threshold. Because fleas are preventable, it is important to prevent a flea infestation in a dog with food allergy.

Abb. GG1ZIZNC: Diagram illustration the allergic threshold.


For treats or variety during the food trial, dry kibble of the trial food can be fed as treats or the canned variety of the trial food can be baked into crunchy dog biscuits.

It is important to keep good records during the food trial. If your dog does sneak a food other than the food trial, a note should be made. This will be important if he continues to have an allergic response.

Update version: 4/24/2014, © Copyright by
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