Hôpital Vétérinaire de L'Île-Perrot Inc.


Seasonal Atopic Dermatitis

August 31, 2017

Your pet is scratching, biting or excessively licking his skin. Did you know that he could be suffering from allergies?

There are many types of allergies : seasonal or annual atopic dermatitis, food allergies, allergies to insect bites and contact dermatitis.


When allergies are caused by an abnormal reaction by the immune system towards allergens present in the environment, we refer to them as atopy. It is caused by contact of the allergens with the skin and is the principal cause of allergies in dogs and cats.

These allergens vary : pollen from trees, plants, and weeds, dust mites, mould, feathers, fur, etc. Depending on the type of allergen, the allergic reaction could have a seasonal cycle (pollen) or may persist the entire year (as in the case of dust, fur or dust mites).

Seasonal atopy coincides with a specific time of the year, appearing after the snow has melted and disappearing after the first snows of winter, only to reappear again the following year at the same time.

In humans, the most common symptoms of seasonal allergies (”hay fever”) include nasal congestion and sneezing, but in animals the symptoms manifest themselves through the skin.



In Quebec, pollens are present in the air during three distinct periods :

  • In spring due to the pollen from trees and bushes.
  • At the beginning of summer due to common herbs such as grass.
  • At the end of July until the beginning of autumn due to ragweed.

In this article we will focus on seasonal allergies.


What are the symptoms?

The most common symptom is itchiness. The pet will scratch, lick and bite, particularly in the areas of the paws, armpits, abdomen, flanks, face, and ears. Basically, the regions that come in contact with pollens.

The dog or cat that develops seasonal allergies will remain allergic all his life. It is a recurring, chronic illness. However, the intensity of the symptoms may vary from year to year depending on the amount of pollen in the air.

Inflammation and damage to the skin caused by scratching can be intense, causing complications such as secondary infections. The micro-organisms (bacteria or yeast) normally present on the skin may increase abnormally, penetrate the surface of the skin, and cause an infection. A pet with atopy is not contagious, even if the skin is infected with bacteria or yeast.

Your pet could present other symptoms as well :

  • Redness
  • Spots or pimples
  • Scabs
  • Loss of hair
  • Oily fur, bad odour
  • Pigmentation and thickening of skin
  • Hives that are red and oozing, or pimples on the lips (in cats).
  • Excessive grooming (in cats).
  • Ear infections
  • Runny eyes, conjunctivitis
  • Nasal secretions

How is Atopy diagnosed?

The diagnosis will be established during a physical exam. The symptoms, the location of lesions, the presence of a seasonal pattern, the age of the pet, the breed of animal and the response to previous treatment all help to guide the diagnosis. The veterinarian may need to perform several tests in order to arrive at a conclusion and to rule out other possible causes of itchiness such as skin parasites, infectious illness, or food allergies. Your veterinarian may recommend skin scrapings, cytologies, fungal cultures or a trial with a hypoallergenic diet for a period of several weeks.

Atopy develops most commonly in young adults aged 1 to 3 years. The origin of Atopy is genetic and often hereditary. Skin allergies are reported to be more frequent in the breeds of dogs listed below, but other breeds are implicated as well.

  • Golden Retriever
  • Labrador
  • English, French Bulldog
  • American Staffordshire Terrier
  • Boxer
  • West Highland Terrier
  • Yorkshire Terrier
  • Lhassa Apso, Shih Tzu
  • Setters
  • Fox Terrier

How to treat Atopy

It is important to consult a veterinarian as soon as itchiness or lesions are present. The risk of infections and lesions increases if the symptoms are not addressed.
Successful management of seasonal allergies is possible with a broad approach.

Treatment of symptoms

A variety of medications exist that help to control itchiness and reduce inflammation of the skin of your pet during allergy season. These include antihistamines, cortisone, and cyclosporine. The veterinarian will make a choice of medications based on the severity and intensity of the inflammation. The dosage will be adjusted accordingly.
It is important to note that these medications do not cure the animal of his allergies, but simply help to control the most uncomfortable symptoms. If the treatment is stopped, the symptoms quickly redevelop if pollens causing the allergy are still circulating in the environment.

Antihistamines diminish the effect of histamine that is liberated in the body at the time of an allergic reaction and is responsible for the symptoms. Used alone, antihistamines are sufficient to control only light to moderate allergy symptoms. If a more powerful treatment is necessary, antihistamines will be used simultaneously with cortisone, ence reducing the dose of cortisone needed to control the symptoms.

Certain antihistamines sold under prescription are more effective in treating the symptoms of dogs and cats than over-the-counter remedies. Please note that 2nd generation antihistamines (Reactine, Aerius, Claritin) have little to no effect on cats and dogs.

Cortisone (prednisone, prednisolone, Vanectyl P*) is a more effective medication than antihistamines for controlling allergies since it is essentially an anti-inflammatory for the immune system. This medication can only be purchased by prescription. A physical exam is required in order to ensure there are no contra-indications for using these medications. Often, a combination of cortisone and antihistamines is recommended. These medications working together, permit the administration of less cortisone, reducing the incidents of side effects associated with cortisone.
Cortisone is available in pill-form but is also available in ointment, spray, or shampoo. Topical cortisone treatments may reduce the need for oral cortisone, thereby reducing the possibility of side-effects.

*Vanectyl-P contains both an antihistamine and prednisolone

How to use cortisone
The goal is to use the smallest possible dose to control symptoms thereby reducing the occurrence of side effects.
Cortisone is administered every day at the start of treatment in order to resolve inflammation and other symptoms. The dosage is gradually diminished until the smallest effective dose, administered every 48 hours, is determined. Administering cortisone every 48 hours as opposed to every day diminishes the risk of atrophy (diminished size and functioning) of the adrenal glands of the patient.
If symptoms begin to reoccur while gradually lowering the dose of cortisone, this indicates that the new dose is not sufficient in controlling the allergy symptoms and the last efficient dose should be used as the smallest possible dose. Unlike antibiotics, we must adapt the dosage to the needs of the pet without giving more than the recommended dosage as indicated by the veterinarian.

Side effects of cortisone
Many people have expressed their concerns for prescribing cortisone to their pets. These worries are based on personal experience or that of someone they know who has used this class of medication. Happily, cortisone is much better tolerated by cats and dogs than by humans. The side-effects are often temporary and disappear rapidly over the course of treatment, especially with the diminishing of the dose.

  • Increase in the production of urine (larger loss of water by the kidneys) which causes an increase in thirst to compensate for dehydration. The severity of this side effect varies from one patient to another. Some dogs will need to be taken outside more often to avoid accidents in the house. Because cortisone does not directly cause thirst, but is implicated more in the loss of water by the kidneys, restriction of water is never recommended as a means to control this side effect.
  • Increase in appetite. Cortisone itself will not cause weight gain unless you permit your pet to consume more calories. The control of calories is essential in avoiding weight gain during the course of treatment.
  • Panting.
  • Lethargy and lack of endurance during physical exercise.
  • If your pet must take cortisone for a prolonged period of time, other problems may surface (diabetes, predisposition to infection, development of Cushing disease, atrophy of the adrenal glands, etc), particularly if the medication is administered every day at a high dose.
  • Because cortisone causes a reduction in the immune defense system it is important to advise your veterinarian of any signs of infection (eyes, ears, skin, respiratory system, etc). If your pet has a reduced appetite, vomiting, or diarrhea, stop the administration of cortisone and contact your veterinarian as soon as possible.

Cyclosporine (Atopica) is an immunosuppressant that has been used successfully in recent years to control symptoms of atopy. It is an effective medication, without the side-effects of cortisone, but is used sparingly due to its elevated cost compared to other treatments.

Apoquel and Cytopoint: Revolutionary products for treating atopy in dogs

Essential fatty acids (Omega 3’s) are considered an aide to treatment. These fatty acids contain natural anti-inflammatory properties.

How to treat atopy – Treatment of secondary infections

Inflammation of the skin caused by allergies affects the skin’s natural defense mechanisms. This results in a higher risk of secondary infections. These infections are also favored by the physical trauma a pet inflicts on his skin by scratching, biting, licking, and rubbing. Like a vicious circle, these infections exacerbate the itchiness caused by the allergies. The infection must be addressed correctly or the treatment for allergies will fail.
Skin cytologies guide the veterinarian in selecting the ideal medication to treat these infections which could be bacterial or fungal in origin and require different medical approaches. Treatment could be in oral, cream, spray or shampoo form.

How to treat atopy – Treatment by desensitization

Desensitization consists of administering to the patient the allergens to which they have reactions in increasing doses. The objective is to induce a long-term level of tolerance to pollens to which there is an allergic reaction.
Due to the costs associated with this type of treatment and the effort required on the part of the owner, this option is reserved for particular patients: Those with seasonal allergies lasting more than 2 – 3 months, those who present with very severe, difficult to control symptoms despite the usual treatments, or those for which the usual medications are contra-indicated.
Once the diagnosis is established, the patient is referred to a specialist in veterinary dermatology to begin the process of desensitization. The specialist will administer tests to identify the specific allergens in the environment to which the pet is allergic.

There are two types of tests used in determining allergens:
1) The first is called an intradermal allergy test which consists of carefully observing the patient’s skin for reaction after specific allergens are injected under the skin. This test may only be used when the skin is not irritated or infected. The patient must not have taken cortisone for at least 3 weeks and antihistamines for at least 10 days prior to the administration of the test.
2) The second is a blood test (serology) in which antibodies against different allergens in the environment are detected in the blood stream during the period of active allergies.
The consensus in dermatology is to proceed with the skin test first which is more reliable.

Once the allergens are identified it is possible to start desensitizing the immune system of the pet with the aid of injections administered at home. At the beginning, injections are given once per week in increasing doses. The dermatologist adjust the schedule and dosage given the reaction and tolerance of the patient. Therapy may continue for several months to several years. This treatment rarely causes side effects. In fact, about 70% of animals will benefit from this type of therapy.

How to treat atopy – Decontaminate the environment and control access

  • Keep your pet away from freshly mowed grass. Collect cuttings and dead leaves immediately.
  • During allergy season avoid taking your pet for walks in fields or open spaces, especially if the pet has shown an exacerbation of his allergies after previously been there.
  • Remove ragweed from your yard as soon as it appears. Ragweed is responsible for most cases of allergies diagnosed in clinic from the end of July to end the end of August.
  • Regular bathing helps to remove pollens from the skin and fur. Consult your veterinarian for advice on which type of shampoo would be best for your pet.
  • Administer a veterinarian recommended flea protection every month during the summer. Dogs that suffer from atopic dermatitis may also be very sensitive to flea bites.


Seasonal allergies are a common problem amongst our four-footed friends.
Veterinarians estimate that about 14.4% of dogs are affected. About two-thirds of these are chronic cases according to studies presented by Novartis Animal Health Canada.
Pets affected by seasonal allergies require specific care. Consulting your veterinarian as soon as possible could help to soothe your pets discomfort and avoid secondary infections.
Our veterinarians will take the time to guide you in finding a convenient solution to this annual annoyance.

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