Skin Allergies and Reactions in Dogs

The number of dogs with allergies has increased dramatically in recent years. It is now estimated that one in seven dogs suffer from allergic symptoms. According to Veterinary Pet Insurance, skin allergies are now the most common reason dog owners take their dog to the veterinarian. Heredity plays a role. Although certain breeds appear to be more allergy prone, all breeds and their mixes can be affected.

An allergy is in an unpleasant reaction caused by exposure to a food, inhalant, or something in the dog's environment. What the dog is exposed to is called the allergen. The way in which the dog's immune system responds to the allergen is the allergic or hypersensitivity reaction.

Before a dog can have an allergic reaction, she must be exposed to the allergen at least twice. The first exposure causes the immune system to manufacture antibodies to the allergen. A later exposure triggers an allergen-antibody reaction that releases histamine, the chemical mediator responsible for the reaction.

While humans tend to experience upper respiratory symptoms when an allergy is triggered, the target organ in dogs is usually the skin, with intense itching being the principal sign. Dogs with allergies often scratch continuously and are miserable, snappish, and generally unpleasant to be around.

There are two kinds of hypersensitivity. The immediate type occurs minutes after exposure and usually produces hives. The delayed response occurs hours or days later and causes intense itching. Anaphylactic shock is a severe hypersensitivity reaction of the immediate type, accompanied by diarrhea, vomiting, weakness, difficulty breathing with stridor, collapse, and, if untreated, death.

Canine allergies fall into four categories:

  • Those caused by fleas and other biting insects (flea allergy dermatitis)
  • Those caused by inhaled allergens such as dust mites, grasses, molds, and tree and weed pollens (canine atopy)
  • Those caused and by foods and drugs (food allergies)
  • Those caused by irritants that have direct contact with the skin (contact allergies)

Hives

Hives are an allergic reaction characterized by the sudden appearance of raised, circular, itchy wheals on the skin of the face and elsewhere. The hair sticks out in little patches. Frequently, the eyelids will also swell. Hives generally appear within 30 minutes of exposure and disappear within 24 hours.

Insect bites are a common cause of hives. Hives can occur after a vaccination. Penicillin, tetracycline, and other antibiotics can produce hives. Topical insecticides and soaps are other causes. Hives that come and go usually are caused by an allergen in the dog's environment.

Treatment: When possible, identify the allergen and prevent further exposure. When a food allergy is suspected, modify the dog's diet. When hives appear shortly after a shampoo or application of a topical insecticide, bathe the dog and rinse thoroughly to remove the chemical from the dog's coat and skin.

Hives usually respond well to an antihistamine such as Benadryl. Cortisone may be needed to control a severe case. Consult your veterinarian.

Flea Allergy Dermatitis

This is the most common allergy in dogs. It is caused by a hypersensitivity reaction to one or more substances in the saliva of fleas. Flea allergy dermatitis is an allergic reaction of both the immediate and delayed type; itching begins immediately and tends to persist long after fleas have been eliminated. One bite is enough to trigger this reaction. Symptoms are worse in midsummer during the flea season. However, dogs who live in the house may suffer all year long if fleas are present.

Flea allergy dermatitis is characterized by severe itching with inflamed skin and red papules found where fleas are heavily concentrated-over the rump and base of the tail, under the legs, and on the groin and belly. Dogs chew and rub at these areas. Hair falls out and the skin becomes dry and scaly. In some cases the skin breaks down and develops raw areas that become crusted and infected. In time, the skin becomes thick and darkly pigmented.

The diagnosis can be suspected by finding fleas on the dog and seeing the characteristic skin rash. Check for fleas by standing your dog over a sheet of white paper and brushing the coat. White and black grains of sandy material that drop onto the paper are flea eggs and feces. An allergic response to flea saliva can be confirmed with an intradermal skin test.

Treatment: The majority of dogs with flea allergy dermatitis can be cured by eliminating fleas on the dog and controlling fleas in the environment. All pets in the household, even those who are not affected, must be treated simultaneously to eliminate fleas. Antihistamines and/or corticosteroids may be required for two to three days to control itching. A medicated bath may also help to make your dog more comfortable. Pyoderma requires topical and oral antibiotics. Seek veterinary attention for these problems.

This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.