Immunotherapy (Allergy Shots) For Cats

What is immunotherapy?

Also known as allergen immunotherapy (AIT), allergen-specific immunotherapy (ASIT) or allergy shots, immunotherapy is a safe and effective treatment for airborne allergens (atophy) in cats. The immune system is responsible for defending the cat against infection from viruses, bacteria and other disease-causing organisms. An allergy is an inappropriate immune response to a harmless substance (known as an allergen). Some allergies can be managed by avoiding the allergen (such as flea bite hypersensitivity or food allergies). Immunotherapy can be of use for cats with atophy. Common triggers for atopic dermatitis include grass and tree pollens, dust mites, storage mites and mould spores.

The goal of immunotherapy is to administer increasing doses of known allergens to train the cat’s immune system to ignore perceived allergens. Treatment can lead to partial or complete remission of allergies with a success rate of 60 – 78%. Traditionally, treatment for atopic dermatitis was aimed at managing clinical signs with glucocorticoids and immunosuppressants.  Immunotherapy can be administered via subcutaneous injection or oromucosal spray formulations.

Symptoms of allergies

Allergies in cats typically affect the skin, common symptoms include:

  • Pruritis (itchy skin)
  • Excessive grooming
  • Hair loss with red and inflamed skin
  • Secondary bacterial or fungal infection


Immunotherapy (allergy shots) should be explored for cats whose symptoms are not adequately controlled by medications or avoidance measures if the side effects of medications are unacceptable or for caregivers who want to reduce the long-term use of medications.

Diagnosing the cause

Before immunotherapy can be started, it is necessary to rule out other potential causes such as mites or fungal infection as well as determine the allergen. This will include the following:

  • Skin scrapings: A skin scraping test uses a scalpel blade to gently scrape along the surface of the skin which is then evaluated under a microscope to look for the presence of mites.
  • Food elimination trial: A food trial is a diagnostic test to determine if a cat has a food allergy. During the 8 to 12-week trial, the cat will be fed a novel source of protein while monitoring for a reduction in clinical signs. The cat is then challenged by resuming the former diet to see if allergic symptoms return.
  • Blister biopsy: A tissue sample is collected by a punch tool to penetrate all the layers of the skin and examined under the microscope to rule out pemphigus.
  • Flea treatment: Diligent flea treatment of all pets in the household as well as the home to rule out flea allergy.
  • Skin prick test: Once it has been determined that the cat has an allergy, it will be necessary to determine the allergen. A sedative will be administered and the cat’s lateral thorax (side) is shaved and marked with a series of dots. The clinician applies each allergen to the marked spot and gently pricks the skin with a sterile lancet so that a small amount of the allergen penetrates the skin. The first two substances are a positive histamine control which produces a raised, red wheal, and a negative control which is a saline solution the allergens are suspended in.


Allergen doses are measured in units called PNU (protein nitrogen units). The first vials will be at the weakest possible dose (1,000-2,000 PNU per ml), and over time, the cat will receive a higher concentration of the allergen, followed by a maintenance dose which is typically given every two to four weeks. The concentration and frequency of administration will be tailored for your cat. Typically, the induction period lasts for four weeks to four months followed by the maintenance dose every three to four weeks.

Your veterinarian may choose to administer the medications or will show you how to do so if you are comfortable with the idea. The cat should be observed for 30 minutes after the injection to watch for side effects which can range from mild to severe.

If the cat experiences mild side effects, the veterinarian may recommend a dose of antihistamines 1-2 hours before the injection can help. Always notify your cat’s veterinarian of any side effects, no matter how mild.

Side effects:

The most common side-effect is itchiness during the induction phase which can last 24-48 hours post-injection.


  • Anaphylaxis
  • Localised swelling at the site of the injection
  • Pruritis

Moderate to severe

It can take up to one year to see an improvement, with an average timeframe of 3 – 8 months. While allergy shots usually won’t cure the allergy, they can significantly reduce symptoms. Allergen avoidance (where possible), along with immunotherapy and managing symptoms with antihistamines, fatty acids, low-dose glucocorticoids and ciclosporin can greatly improve the cat’s quality of life.

Frequently asked questions

How much do allergy shots cost?

Allergy shots cost in the range of $100 per week, but this can vary depending on the number of allergens in the shot.

How long will the cat receive allergy shots?

Most cats will require allergy shots for life, although it may be possible to discontinue allergy shots after two to three years to see how the cat responds.


  • Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio