What is an allergy?

An allergy is a state of over-reactivity or hypersensitivity of the immune system to a particular substance called an allergen. Most allergens are proteins.

The allergen protein may be of insect, plant or animal origin. Exposure to the allergen, usually on multiple occasions, sensitizes the immune system, and a subsequent exposure to the same or related allergen causes an over-reaction. Normally the immune response protects the dog against infection and disease, but with allergies, the immune response can actually be harmful to the body.

The immune reactions involved in allergies are quite complex. Most reactions involve an antibody in the blood called Immunoglobulin E (IgE). In an allergic reaction the allergen protein molecules combine with IgE antibody molecules and attach to a type of cell called a mast cell. Mast cells are found in many tissues throughout the body. When the antigen and antibody react with mast cells, the mast cells break up and release potent chemicals such as histamines that cause local inflammation (redness, swelling and itching). This inflammation causes the various signs associated with an allergic reaction.

What are the symptoms of allergies in dogs?

In the dog, the most common symptom associated with allergies is itching of the skin, either localized (in one area) or generalized (all over the body). In some cases, the symptoms involve the respiratory system, with coughing, sneezing, and/or wheezing. Sometimes, there may be runny discharge from eyes or nose. In other cases, the allergic symptoms affect the digestive system resulting in vomiting and diarrhea.

How common are allergies in dogs?

Unfortunately, allergies are quite common in dogs of all breeds and backgrounds. Most allergies appear after the pet is six months of age with the majority of affected dogs over age two.

Are allergies inherited?

Some allergies are inherited. The inherited trait is known as Atopy (see What is Inhalant Allergy or Atopybelow).

What are the common allergy-causing substances (allergens)?

A very large number of substances can act as allergens. Most are proteins of insect, plant or animal origin, but small chemical molecules known as haptens can also cause allergy. Examples of common allergens are pollens, mold spores, dust mites, shed skin cells (similar to “pet allergies” in humans), insect proteins such as flea saliva, and some medications.

What are the different types of allergy?

There are several ways of classifying allergies. Some examples of classifications include:

  • Precipitating allergen – Flea Allergy
  • Route the allergen takes into the body – Inhalant Allergy, Skin Contact Allergy or Food Allergy
  • Time it takes for the immune reaction – Immediate-type Hypersensitivity, also called Anaphylaxis or Shock, and Delayed-type Hypersensitivity
  • Type of immune reaction – Types I through IV Hypersensitivity
  • Clinical Signs – Allergic Dermatitis or Allergic Bronchitis
  • Inherited forms – Atopy or Seasonal Allergies

What is Contact Allergy?

Contact allergy is the least common type of allergy in dogs. It results from direct contact to allergens, such as pyrethrins found in flea collars, pesticides used on the lawn, grasses, materials such as wool or synthetics used in carpets or bedding, etc.

If the dog is allergic to these substances, there will be skin irritation and itching at the points of contact, usually the feet and stomach. Removal of the allergen (once it can be identified) often solves the problem.

What is Flea or Insect Bite Allergy and how is it treated?

Insect bite allergy is the exaggerated inflammatory response to the bite or sting of an insect. Arachnids such as spiders and ticks, and Insects including fleas, black flies, deerflies, horseflies, mosquitoes, ants, bees, hornets and wasps, and arachnids such as spiders and ticks can　cause an allergic reaction in sensitive dogs. Flea saliva is the most common insect allergen. Most dogs experience minor local irritation from fleabites. The allergic dog will react to a single bite with severe local itching. It will bite and scratch itself and may remove large amounts of hair, especially in the tail-base region. A secondary bacterial infection may develop in the broken skin. The area most commonly involved is over the rump in the tail-base region and extending down the hind limbs.

What is Inhalant Allergy (Atopy) and how is it treated?