Many dogs experience skin conditions throughout their lifetime, and the bulk of these are caused by allergies. Canines react to many of the same allergens as humans, specifically flea bites, dust and dust mites, trees, grasses, weed pollens, milk and dairy products, foods and food additives (usually meats, grains, and chemical preservatives), rubber and plastic materials, and fabrics like nylon and wool.
Exposure to an allergen causes the affected dog's immune response to kick into gear, in an attempt to protect the dog. It does this by producing a protein known as IgE, which in turn attaches itself to "mast cells," which are disease-fighting white blood cells located in the animal's skin. This process also releases chemicals like histamine, which create many of the irritating symptoms of an allergy, including a runny nose.
Allergic symptoms in dogs include: scratching, mutilated skin, hair loss, rubbing their face on the carpet, chewing the feet, and recurrent ear infections. These symptoms remain consistent regardless of whether the animal's allergy is in response to a food, an inhalant (like pollen) or an insect bite. The foot-chewing occurs because the only places a dog has sweat glands are on its feet, and these glands become inflamed during an allergic reaction. Finally, the ear infections appear because wax-producing glands inside the dog's ear overproduce in response to the allergen. These wax deposits in turn often play host to colonies of bacteria and yeast that flourish and create chronic infections.
Dogs with allergies often scratch until their skin is raw, bleeding, and/or scarred. Depending upon the dog, the skin also may become oily, reddened, or dry and crusty. Often the wounds inflicted by a scratching dog end up leading to bacterial infections in the skin, creating irritation on top of initial allergic reaction. Patchy hair loss usually accompanies the skin irritation.
About 80 percent of all canine allergies develop when the dog is between one and three years old, although they have been known to develop in dogs as old as six to eight. Animals that are diagnosed as young dogs often develop allergies to additional substances as they age. Or, their existing allergy (to tree pollen, for example) can suddenly become more severe.
In most cases a dog must be exposed to the allergen for a period of months or even years before a full-fledged allergy develops. (The exception to this is an insect bite; it may only take a few bites before a vulnerable animal develops an allergic reaction.) The allergic response also can be "learned" by a dog's immune system and then passed along genetically to its offspring. Inherited allergies are seen frequently in breeds like Dalmatians, English Bulldogs, English and Irish Setters, Llasa Apsos, Miniature Schnauzers, Pugs, and all types of Terrier, especially Cairn, Scottish, West Highland White, and Wire-Haired Fox Terriers.
Allergies in pets are usually diagnosed through skin or blood testing, and by eliminating different allergens from the dog's environment until the culprit is isolated. Once identified, the pet must be kept away from the allergen as much as possible, which usually means significant lifestyle changes for both owner and pet. Your veterinarian can advise you on appropriate steps to take to minimize the effects of allergies and make your pet more comfortable.