Merck Manual

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Allergies in Dogs

By

Stephen D. White

, DVM, DACVD, University of California, Davis;


Karen A. Moriello

, DVM, DACVD, Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison

Last full review/revision Jun 2018 | Content last modified Jun 2018

Like people, dogs can be allergic to various substances, including plant particles and other substances in the air or substances in food. These substances are called allergens. Allergens are substances that, when inhaled or absorbed through the skin, respiratory tract, or gastrointestinal tract, stimulate the immune system and the release of histamine and other substances. This results in inflammation, signs of which include reddening of the skin (erythema), swelling (edema), and itching (pruritis).

Airborne Allergies (Atopy or Canine Atopic Dermatitis)

It is thought that dogs are genetically predisposed to become sensitized to allergens in the environment. Both male and female dogs can be allergic to materials in the air. Breeds predisposed to developing allergies include Chinese Shar-Peis, Wirehaired Fox Terriers, Golden Retrievers, Dalmatians, Boxers, Boston Terriers, Labrador Retrievers, Lhasa Apsos, Scottish Terriers, Shih Tzus, and West Highland White Terriers. However, any dog of any breed (or mixed breeds) can be allergic. The age of onset is generally between 6 months and 3 years. Signs are usually seasonal but may be seen all year. Itching is the most typical sign. The feet, face, ears, front legs, and abdomen are the most frequently affected areas, but scratching all over the body is common. Scratching can lead to secondary signs of wounds, scabbing, skin and ear infections, hair loss, and scaling. Other signs of atopy include licking or chewing the paws and rubbing the face and eyes. The skin is the main target of atopic dermatitis, but about 15% of affected dogs also develop inflammation inside the nose (rhinitis) and asthma. Longterm or recurrent ear infections may be the only sign in a small number of dogs.

The diagnosis of airborne allergies is difficult because there are no tests available that can positively identify the condition. Instead, diagnosis is based on age, breed, signs, and disease history (such as age when the signs first started and response to treatment). Other causes of signs must be excluded. Allergy testing cannot diagnose allergies, but it can be used to identify the offending allergens and to formulate a specific immunotherapy treatment program.

Atopic dermatitis is a lifelong disease that requires longterm management and regular veterinary examinations. Treatment involves a number of options: avoidance of the offending allergen(s), controlling the signs of itching, bathing and improving coat hygiene, controlling flare factors (such as fleas or secondary infections), and immunotherapy (for example, an allergy vaccine). A good management plan requires the use of several different treatments, the understanding and reasonable expectations for response from the pet owner, and frequent progress evaluations so that the plan can be adjusted as needed. Treatments used for sudden flare-ups often vary from those used for longterm management. Follow your veterinarian's instructions closely.

Immunotherapy attempts to increase a dog’s tolerance to environmental allergens. It is the preferred treatment of most veterinary dermatologists and allergists. Allergy vaccine (allergy shot) preparation involves selection of individual allergens for a particular dog. The allergen selection is determined by matching the test results with the prominent allergens during the time of year when the dog has signs. Immunotherapy can be administered as injections or as allergy drops. The dog must be cooperative enough to receive allergy injections or drops. If injections are used, you may have to administer some doses yourself. Your veterinarian can provide training and most owners learn to administer the allergy injections very well, while others may need assistance from a capable friend or veterinary staff member. Your veterinarian will determine the frequency of the treatments and the dosage given.

Treatment takes a longterm commitment. You must be willing to follow instructions accurately, be patient, and be able to communicate effectively with your veterinarian. Treatment may initially increase signs. If this occurs, contact your veterinarian immediately. Improvement may not be visible for 6 months, and a year of treatment may be required before you can tell if the immunotherapy is working. The best way to evaluate the treatment is to compare the degree of disease or discomfort between similar seasons. Anti-itch medication and antibiotics are often required during the initial phase of treatment and may be necessary intermittently throughout the year. Do not assume that immunotherapy has failed if signs appear during therapy because they may be due to another cause (such as an infection). Talk to your veterinarian if signs return, change, or do not resolve during treatment.

Allergy shots improve the condition but do not cure the disease. Many animals may still require anti-itch medications during seasonal flare-ups.

Food Allergies

Among pets, food allergies are less common than airborne allergies. Any breed can develop food allergies, but there may be an increased risk for Labrador Retrievers, West Highland White Terriers, and Cocker Spaniels. Signs of food allergy are similar to airborne allergies except there is little variation in the intensity of itching from one season to another. The age of onset is variable. The distribution and intensity of itching varies between animals.

Food allergies are diagnosed by feeding a limited foodstuff (elimination or hydrolyzed) diet and seeing if the itching resolves. Blood and skin tests are not reliable for diagnosis. Your veterinarian should be consulted to develop a specific test plan for your dog. The ideal food elimination diet should be balanced and nutritionally complete and not contain any ingredients that have been fed previously to your dog. Owners often do not understand that if any previously fed ingredient is present in the elimination diet, the dog may be allergic to that one ingredient and the diet trial will be a failure. The key point in any food elimination diet trial is that only novel food ingredients can be fed. This also includes treats and anything the dog eats besides its regular food (including table food, flavored medications, and toothpaste). An alternative to an elimination diet is a prescription diet that contains hydrolyzed proteins. These proteins are broken down into components that your dog's body no longer recognizes. Whichever diet is chosen, dogs should only eat the food and treats recommended by their veterinarian during the duration of the trial.

The trial diet should be fed for up to 3 months. If marked or complete resolution in signs occurs during the elimination diet trial, food allergy can be suspected. To confirm that a food allergy exists and improvement was not just coincidental, the dog must be given the previously fed food ingredients and a relapse of signs must occur. The return of signs is usually between 1 hour and 14 days. Once a food allergy is confirmed, the elimination diet should be continued until signs disappear, which usually takes less than 14 days. At this point, previously fed individual ingredients should be added to the elimination diet for a period of up to 14 days. If signs reappear, the individual ingredient is considered a cause of the food allergy.

The foods dogs are most often allergic to include beef, chicken, eggs, corn, wheat, soy, and milk. Once the offending allergens are identified, control of the food allergy is by strict avoidance. If your dog is allergic to other things (such as plant pollen or fleas), identifying underlying food allergies will be harder. Infrequently, a dog will react to new food allergens as it ages.

For More Information

Also see professional content regarding food allergies or atopy.

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