Dog's Itchy Skin Can Indicate Allergy

By: Kim Marie Labak
University of Illinois College of Veterinary Medicine

Just like people, dogs can suffer seasonal skin allergies to environmental allergens such as pollen, dust mites, and insect bites. According to Dr. Karen Campbell, Chief of Specialty Medicine at the University of Illinois Veterinary Teaching Hospital in Urbana, there are effective ways to diagnose and treat skin allergies.

Allergic reactions occur when the immune system overreacts or responds inappropriately to an otherwise innocuous substance. Often there is no sign of allergy the first time an animal is exposed, but after that first exposure, the immune system builds up a reserve of antibodies to react to that particular allergen. The next time the animal encounters the same allergen, the immune system reacts strongly.

Predisposition to skin allergies is inherited, and many breeds, such as terriers, Dalmatians, golden retrievers, schnauzers, and poodles, are more prone to allergies. Some geographical regions also predispose both humans and dogs to allergies, since certain environments harbor a wider variety of allergens.

Dr. Campbell explains that immune systems are more prone to developing allergies in the first three or four years of life. Animals that develop allergies when they are very young (e.g., less than one year old) are likely to develop more as they get older. "However," Dr. Campbell says, "after two or three seasons of exposure to allergens, a dog won't get too many new allergies unless it moves to a new geographical location with a new environment and new allergens."

Many things in the environment can cause allergies, and combinations of allergens can result in an additive effect; for example, a dog reacting to a food allergy plus a dust mite allergy plus a ragweed allergy will have more severe symptoms than a dog allergic to only one substance.

Skin allergies usually show up as problems involving the ears, feet, face, armpit, and genital regions that have thin skin or a lot of contact with the environment. Skin reactions involve inflammation, itchy irritation, and moist secretions.

This moist, inflamed skin attracts many microorganisms, so often a skin allergy can lead to bacterial infections. Smelly yeast infections in the ear are commonly associated with allergies. Scratching can also lead to rashes or sores that become infected. Once a skin infection sets in, a vicious cycle begins: the infection causes more inflammation, which attracts more bacteria, which causes more inflammation, and so on.

A very common source of skin allergies is flea or mite bites. Saliva and other secretions from these parasites can cause itchy hypersensitivity reactions; the surrounding skin releases histamine and other substances that cause itching and inflammation.

Parasites, both internal and external, can contribute to development of new allergies. As the immune system creates antibodies to the parasites (such as fleas, mites, intestinal worms and heartworms), it may also develop sensitivities to other otherwise harmless environmental substances. Keeping dogs free from parasites, especially while they are puppies, is an essential step in preventing allergies.

An itchy dog can be tested for allergies through blood tests; high amounts of a certain antibody, called IgE, usually indicate an overreaction to an allergen. Also, veterinarians can perform skin tests, similar to those performed on people, by exposing small areas of skin to different allergens and observing how the skin reacts to each allergen. Interestingly, dogs are often sensitive to allergens similar to the ones that affect people, but dogs react differently because the route of exposure and biochemistry of the reaction is very different.

Once an allergy is diagnosed, there are several strategies for treatment. Avoidance of a specific allergen may be difficult, but some household changes are feasible, such as keeping a dog away from down pillows if it is allergic to feathers. Since environmental allergens are usually absorbed through the skin, weekly bathing can prevent itchiness, washing allergens away before they get a chance to penetrate the skin.

If an allergen cannot be washed away or avoided, fatty acid supplements in the diet can help reduce skin problems. Many drug treatments, such as antihistamines, anti-inflammatory corticosteroids, and immunosuppressive drugs, can reduce the symptoms, but these drugs generally come with side effects. Another option is immunotherapy, which involves desensitization to the allergen by a series of allergy shots.

For more information about environmental skin allergies, contact your local veterinarian.

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