Allergies can occur in any breed of dog or cat. While some breeds are heavily represented, approximately 1 of every 5 dogs has an allergy of some type. An allergy can be defined as the body’s immune reaction to a substance it comes in contact with. These substances, called allergens, are usually proteins and can contact through the respiratory tract, the digestive tract, food allergies, and/or the skin, contact allergies. Environmental allergies account for 90% of all allergic reactions while food allergies and contact allergies are relatively uncommon. The most common contact allergy is flea bite allergies which is discussed under Fleas and Flea Preventative. Food allergies are discussed under Food Allergies.

Environmental Allergies
Environmental allergies affect dogs and cats at a young age, sometimes beginning as early as 6 months of age. Occasionally, older pets can develop environmental allergies. An environmental allergy reaction begins by the dog or cat inhaling the allergen into the lungs. Once there, the allergen stimulates the immune system which then goes into action by sending out chemical messengers to the body which trigger histamine release. The symptoms and signs of allergy are expressed where the greatest number of histamine containing cells are found. In humans, these areas are in the eyes, nasal passages, and sinuses. In dogs and cats, the areas most affected include the ears, the feet, and the skin. Dogs will differ between individuals with some having horrible ear problems while others will chew and lick at their feet excessively. When the skin is involved, hair loss occurs and as the dog bites and scratches at an area, it will commonly develop a “hot spot”. A hot spot is an acute infection, usually brought on by the dog licking, chewing, and/or scratching at a particular part of the body which allows bacteria to penetrate deep into the skin. While there are many different substances that can become antigens, the most common can be found in four groups: Molds, Grasses, Trees, and Fall Weeds. Molds are the most common antigen and mold counts will elevate any time there are cool moist evenings followed by warm days. They usually cause problems in Spring and Fall, but can happen any time the conditions are favorable. The second most common allergen is the pollen of fall weeds, Ragweed, and Cockleburr. These reactions will start in late summer/early fall and continue until late fall after a sustained cold spell. Next would be the grass pollens which start in late spring/early summer and continue through the summer. Tree pollens cause less problems because trees usually produce pollen for only a short time, then are done until next year.
Most allergies are only to one group of allergens, however, some dogs will develop reactions to two or more groups. In addition to these four groups, there are inhalant allergies to House Dust, Dust Mites, Kapoc (the stuffing in furniture), and a few other substances.
Allergies are diagnosed based on a patient having typical clinical signs and eliminating other skin or ear problems such as fleas, bacterial infections, mange, or ear mites. What a patient reacts to can be estimated based on when the reaction starts and stops. A patient that is thought to have allergies can be tested either by a blood test or by skin tests to determine what allergens are causing the reaction. This is only done if the owner is committed to going on to desensitization injections.
Treatment for allergies can be frustrating. Ideally, it would be great if the insulting agent could be taken out of the pet’s environment, but removing Ragweed from the Midwest, or Grass pollens from anywhere is not an option. Treatment is targeted at reducing clinical signs of itching.

Antihistamines Work Fast Only effective 25% of the time Benadryl
Inexpensive Must be dosed 2-3 times daily Chlorpheniramine
Few side effects

Essential Fatty Acids No side effects Only effective 25% of the time Fish Oils
Improves haircoats Takes 6 to 8 weeks to work Flax Seed Oil
Not a drug

Corticosteroids Provides immediate relief Serious side effects Prednisone
Over 90% effective Requires prescription Triamcinolone
Cannot give too often

Cyclosporine Provides relief from Suppresses the allergies, Atopica
the itching without does not “cure” them
the use of corticosteroids.

Allergen Testing/
Desensitization Eliminates the allergy More expensive Individualized to
Done in the home Effective 75% of the time the pet.
Can eventually stop Can take up to 1 year to work

In all allergy cases, successful treatment will use a combination of the above treatments, not just relying on one. Successful management of allergies requires a cooperative effort between the pet owner and the veterinarian to select the course of treatment that is most effective and has the least side effects for the patient.