Allergies in Dogs and Cats

Updated: 8/3/23
Dog in the grass scratching


The immune system is the body’s defense against anything that is foreign such as bacteria, viruses, or parasites. Allergies occur when a dog or cat’s immune system overreacts to a substance that isn’t a health threat. Those substances are called allergens.

Atopic dermatitis, also known as atopy, refers to allergies to things in the environment such as dust mites, pollen, mold, trees, grass, fleas, or even another pet. The condition occurs when a pet encounters an allergen either by inhaling it or through direct contact with the skin. Direct contact with the skin explains, in part, why the feet and face can be so itchy — these are the parts of a dog or cat’s body that are most in contact with allergens. Environmental allergies may be either seasonal or year-round depending on if the allergen is seasonal like pollen or present year-round like dust mites.

Food allergies are much less common in pets than environmental allergies. When they occur, the dog tends to be allergic to common ingredients in food such as beef, chicken, milk, soy, or eggs. The foods that cats are most often allergic to include fish, beef, chicken, and milk products.

Much as they are for humans, allergies in pets are itchy, irritating, frustrating, and sometimes painful. On top of this, the itching, scratching, and licking can lead to infections.

Risk Factors


Most allergic dogs begin to show signs when they are between six months and three years old. Any dog can develop environmental allergies, but the condition is more common in the following breeds:

  • Boston terriers
  • Boxers
  • Dalmatians
  • Golden retrievers
  • Labrador retrievers
  • Lhasa apsos
  • Scottish terriers
  • Shar-peis
  • Shih tzus
  • West Highland white terriers
  • Wirehaired fox terriers

Any dog can develop food allergies, but there may be an increased risk for the following breeds:

  • Cocker spaniels
  • Labrador retrievers
  • West Highland white terriers


Most allergic cats begin to show signs before they are five years old. Any cat can develop allergies, but the condition is more common in purebred cats, particularly the following breeds:

  • Abyssinians
  • Devon Rex
  • Maine Coon
  • Ocicats
  • Persians
  • Siamese
  • Somali cats



  • Itching
  • Scratching: The feet, face, ears, front legs, and abdomen are most often affected, but scratching all over the body is also common.
  • Scratching can lead to secondary signs of wounds, scabbing, skin and ear infections, hair loss, and scaling.
  • Licking or chewing the paws
  • Rubbing the face and eyes

Signs of food allergy are similar to those of environmental allergies except there is little variation from one season to another. Gastrointestinal signs such as chronic vomiting, diarrhea, belching, and frequent bowel movements also may occur.


  • Overgrooming
  • Scratching and licking
  • Excessive scratching and licking may lead to sores and other skin conditions, including hair loss, scaling, crusting, and inflammation
  • Inflammation of the nasal passages (rhinitis)
  • Asthma (sneezing, coughing, and wheezing) may also occur.
  • A variety of skin eruptions that can appear just about anywhere on a cat’s body may signal the onset of a condition referred to broadly as eosinophilic granuloma complex (EGC).

Signs of food allergy are similar to those of environmental allergies except there is little variation from one season to another. Gastrointestinal signs such as chronic vomiting and diarrhea may also occur.


Keeping a detailed history of your dog or cat’s itching problem will be useful for the diagnosis. This means monitoring the signs, when the signs occurred, what happened before the onset of the signs, and response to any treatments.

Allergy testing can be very effective in identifying the underlying cause of atopic dermatitis, However, it cannot be used to determine whether or not a patient has atopic dermatitis. Atopic dermatitis must first be diagnosed based on history, clinical signs, and the exclusion of other skin diseases.

Allergy testing for atopic dermatitis typically takes one of two forms: intradermal skin testing or blood (serum) testing. 

skin patch test dogs

Skin patch test on a dog

The standard method for determining if food is the cause of the allergy is a diet elimination trial. Elimination diets contain a limited number of ingredients and protein sources not typically found in common pet food — and not previously fed to your pet. An elimination diet requires determination on the part of the owner to tough out six to eight weeks of strict dietary control. If the itching resolves on the diet elimination trial, additional foods slowly may be added to the diet while your pet is monitored for itching.


It is not possible to cure environmental allergies, but they can be managed. An effective treatment plan may involve several different approaches:

Reduce Allergens  For dogs, simply wiping their face and paws when coming in from outside will help reduce the allergens and thus the chewing and licking. If your dog is itchy all over, a nice soothing bath will help calm the skin.

Parasite Control  One of the top causes of allergies in pets stems from a reaction to flea saliva. A flea bites your dog or cat, setting off an allergic reaction. Fortunately, numerous options for controlling fleas are available. Your veterinarian can help you determine which product best fits your pet’s needs.

Medication A variety of drugs can be used to turn off the allergic reaction underlying the itch-scratch cycle in your pet.

  1. Antihistamines Over-the-counter antihistamines are sometimes used to treat mild clinical signs of allergies.
  2. Steroids Prednisone and other steroids can relieve itching and the resulting inflammation; however, their side effects (increased water drinking, increased urination, and increased appetite) limit long-term use in allergy management.
  3. Prescription allergy medications More commonly, veterinarians use prescription medications to help manage allergies. Some of the drugs are human medications, but one dog-specific treatment, oclacitinib (brand name: Apoquel), inhibits the pathway inside the cell responsible for turning on the itch-scratch cycle. There is also a monthly monoclonal antibody for dogs called lokivetmab (brand name: Cytopoint) that is given by injection.

Immunotherapy Retraining the immune system to turn off the triggered response has been used in allergy management for decades in the form of “allergy shots.” Allergy shots contain a small amount of the trigger substance and, when given at regular intervals, teach the immune system to ignore the trigger.

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AMC's Dermatology Service has a breadth of experience in recognizing, diagnosing, and treating diseases of the skin of animals, including the ear, hair, nail, hoof, and mouth.

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