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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 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.

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