Dog Allergies

Causes, Symptoms, and Treatments

by Dr. Audrey Harvey, BVSc (Hons)

Dog allergies cause skin inflammation and itching, and an affected dog will scratch constantly to try and relieve their discomfort. This common medical condition can be very frustrating as an owner to deal with.

Allergic reactions are caused by an over-sensitive immune system which has an extreme reaction to a foreign substance.

Commonly Affected Dog Breeds

The tendency for dog allergies to develop is hereditary, and some breeds are more likely to suffer from this annoying condition. Small terriers such as the West Highland White Terrier and the Toy Fox Terrier are often affected, as are small fluffy breeds such as the Lhasa Apso. Larger breeds including the Golden Retriever and German Shepherd also suffer from allergies. Having said that, it is possible for any individual dog to become allergic, whatever their breed.

The first time a dog is exposed to an allergen, they don't usually have any reaction. Their immune system will produce antibodies to that allergen, which attach themselves to a particular white blood cell known as a mast cell. Their troubles start the next time they encounter that allergen. It stimulates the antibody loaded mast cells to release histamine and other chemicals, which are responsible for the red, itchy and inflamed skin reaction.

Symptoms of Allergies in Dogs

Allergic reactions tend to first appear when a dog is between 1 and 3 years of age. They aren't likely to occur in puppies. However, some dog allergies don't develop until well into middle age, but this is less common.

Normal dog skin has a resident bacterial and fungal population, which don't usually cause any problems at all. The inflammation associated with an allergic reaction changes the skin surface and allows these organisms to multiply, causing a secondary infection. This infection can also itch, and adds to the dog's discomfort.

The most frequent symptom of dog allergies is a constant itch. These poor dogs get no peace, and are always licking, scratching or biting at themselves.

Depending on the cause of the allergic reaction, affected dogs may lick their feet (acral lick dermatitis), rub their face on the carpet or sneeze. They may also suffer from frequent eye and ear infections.

Dogs with long or dense coats, such as Labrador Retrievers, Golden Retrievers and Rottweilers, can develop hot spots associated with an acute allergic reaction. These are hairless patches of skin, which become red raw, moist and extremely painful. They appear suddenly, often on the face, and spread quickly.

Common Causes of Dog Allergies

1. Flea Allergy Dermatitis

The most common cause of allergic reactions in dogs is a flea bite. Many dogs are bitten by fleas, and while they may scratch once or twice, they are not seriously affected. However, allergic dogs over-react to the saliva, and will develop a severe itch (flea allergy dermatitis). These poor dogs will bite and scratch themselves until they bleed. In fact, dogs with allergies can end up with worn incisors, because hair is very abrasive. Typical parts of the body affected by flea allergy dermatitis are the lower back, hind legs and down the tail, because they are easily reached with the teeth. This, plus the fact that symptoms are worse during summer, is very suggestive of flea allergy.

2. Atopy (Dust and Pollen)

Dogs can develop an allergy to dusts and pollens in the environment, just like hay fever in ourselves. This is called atopy and initially tends to be seasonal, but over time will become a year-round problem. Symptoms of this type of allergy include sneezing, rubbing their face on the carpet or furniture, and licking and biting at their feet. A diagnosis of atopy is often based on a dog's symptoms, and when they are worse. Allergy testing, where tiny amounts of various allergens are injected into the skin to see if a reaction occurs, will help to identify exactly what your dog is sensitive to.

3. Dog Food Allergies

Food sensitivity accounts for less than 10% of dog allergies. While affected dogs may show gastrointestinal signs such as vomiting and diarrhea, they often have itchy skin and chronic ear infection and inflammation. Food allergies can be difficult to diagnose. Changes in diet do not cause food allergies. Dogs become sensitive to a food ingredient after eating that ingredient for some time, often years. This means that the only way to tell if a food is responsible for a dog's itch is to do an elimination diet: feed them a food they have never had before, for up to 8 weeks, and watch their skin for improvement. If there is a good response, then something in their diet is causing their itch.

4. Contact Allergies in Dogs

Contact allergies are the least common allergy in dogs, and occur when a dog's skin reacts to something they touch. Plants, carpets, and topical skin creams and lotions may cause reddening and itching just in the area that has come into contact with the allergen.

Treatment of Dog Allergies

There are really only two ways of treating allergies in dogs. Firstly, keep them away from whatever they are allergic to, and secondly, stop their reaction to the allergen.

Dog Flea Treatments

The first option works well for some allergies. An effective insecticide that kills fleas and stops them from biting will prevent the severe itch associated with flea allergy. Monthly Comfortis tablets work well, as do the topical spot-on treatments such as Advantage and Revolution. To be effective, any flea control program must break the flea life cycle and prevent eggs and larvae in the environment growing into blood sucking adults. Sentinel tablets given monthly will do this, as will a flea fogger or yard spray which contains the chemical methoprene.

Dog Food Allergy Treatments

When a food allergy has been confirmed, a feeding trial will help to identify the culprit. Your dog should be fed one ingredient for two weeks to see if they start itching. For example, add beef to their dinner bowl and watch for a reaction. If they are fine, then you know that beef is not the problem. Then, try with rice. If you identify a problem ingredient, then this goes on the list of foods never to be given to your dog. You will ultimately end up with a list of safe foods, and a list of banned foods. It is often a long drawn out process, but it does work to eliminate these types of dog allergies.

If you have identified what is causing your dog's contact allergy, it should be fairly straightforward to prevent them coming in contact with it.

Also want to talk to your veterinarian about hypoallergenic prescription dog diets. Three common ones are Royal Canin Veterinary Diet Hypoallergenic HP, Purina HA Hypoallergenic dog food, and Hill's Prescription Diet Z/D Ultra Allergen Free dog food.

Dog Atopy Treatment

It is often difficult to keep dusts and pollens away from atopic dogs. Treatment for these types of dog allergies relies on reducing their body's response to the allergen. There are several ways of doing this. The first line of treatment is often medication. Antihistamines will prevent histamine from affecting your dog's skin. They are very safe, but unfortunately most dogs don't respond to them, so their use is limited.

Common dog antihistamines used in dogs are hydroxyzine, diphenhydramine (benadryl), chlorpheniramine, and amitriptyline.

Corticosteroids such as Prednisolone will suppress your dog's immune system and stop it over-reacting. They are very effective, but can have side effects. Weight gain, Cushing's Disease, and liver problems can also occur with long term corticosteroid use. Antihistamines and corticosteroids are effective in treating allergies of any cause, and are often used together with flea control and in the early stages of a food elimination trial, to give your dog immediate relief.

A product called Temaril-P is a combination of corticosteroid and antihistamine has shown some promising results treating dog allergies.

Cyclosporine (Atopica) is a specific medication which is used to treat atopy. Although it takes longer to have an effect, it seems to have a greater safety margin than corticosteroids.

Dog Allergy Shots

Some allergies respond well to desensitizing injections (immunotherapy). Tiny amounts of allergen is injected into your dog, so their immune system gets used to it, and is less likely to react. These injections are extremely safe, but can take several years to be fully effective, and are usually very expensive.

Immunotherapy for dogs has been show to be helpful in about 70% of dog atopy cases.

In many cases, allergic dogs will need antibiotic or anti-fungal treatment to control the secondary infection on their skin. This may involve washing your dog in medicated shampoo, or giving them tablets by mouth.

There are some natural treatments that can help relieve allergic symptoms. Flax seed oil and fish oil both have a natural anti-inflammatory effect and may reduce itching. Oatmeal shampoos and leave-in conditioners will soothe red irritated skin and make your dog feel so much better.

There is no need for an allergic dog to live with constant itching. The appropriate treatment will make them more comfortable, and they'll be able to enjoy life again.

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