Cat and Dog Allergies

One of the most common medical conditions affecting cats and dogs is allergies. An allergy occurs when your pet's immune system overreacts or is hypersensitive to foreign substances (called allergens). 

Allergens are foreign proteins that the body's immune system tries to remove. Reactions can manifest in the skin, respiratory system, and digestive system. 

Skin allergy, or allergic dermatitis, is the most common type of allergic reaction in cats and dogs, and poses the risk of secondary infection. As your cat or dog scratches, bites, and licks at their itchy skin, they risk opening it up to yeast and bacterial infections that then need treatment.

The most common cat and dog allergy symptoms include rash, constant licking, swelling, sneezing, runny eyes, diarrhoea or vomiting, and itchy skin, eyes, and ears.

Main causes of dog skin allergies and cat itchy ears:


Flea allergy dermatitis (FAD) is the most common allergy in cats and dogs. FAD is when your pet has an allergic reaction to flea saliva after a flea bites them. It causes extreme itchiness, especially at the base of the tail, and their skin may become red, inflamed, and scabby. You may also notice other signs of fleas, such as flea dirt, or even see the fleas themselves.


True food allergies are less common and result in an immune response. The symptoms can range from skin conditions (rash, facial swelling, itchiness), gastrointestinal signs (vomiting and/or diarrhoea), or a combination of both. In some rare cases, a severe reaction resulting in anaphylaxis can occur - similar to a severe peanut allergy in humans

Food hypersensitivity or intolerances are more common. Unlike true allergies, intolerances do not involve an immune response and are instead a gradual reaction to an offending ingredient, usually a protein, in your pet’s food. 

Cats and dogs with food sensitivities can present with several symptoms, including vomiting and diarrhoea, itchy skin around ears and paws, poor skin and coat condition, and chronic ear or foot infections.


Dust, pollen, and mould can cause an atopic allergic reaction or atopy. In most cases, these allergies are seasonal so you may only notice your pet itching or sneezing during certain times of the year. 

The most affected areas are the paws and ears, but these allergens may also affect the muzzle, underarms, groin, around the eyes, and between the toes.


This common invasive weed with dark green leaves and small white flowers during Spring is found in moist shady areas in backyards, parks, and riverbanks. It is a leading cause of contact allergies in dogs, causing an itchy rash on their underbelly, armpits, groin, ears, and face.

Air particles

Allergic bronchitis, or asthma, occurs when a cat or dog’s immune system overreacts to an allergen in the air and causes inflammation and constriction of the airway. 

Cigarette smoke, poor environmental hygiene, dusty cat litter, hair spray, moulds, pollen, powders, household chemicals, and air fresheners are all potential allergens.

Wasp and bee stings

Cats and dogs love to chase bees and wasps, so sometimes get stung, which can cause a sudden (acute) allergic reaction. 

The most common places they get stung are their paws, nose, and mouth. Stings generally cause temporary pain, irritation and swelling which is usually mild and rarely a problem, but some pets can have a more severe reaction.

Treatment of cat and dog allergies

The first focus of treatment is prevention: remove the cause of the allergy where possible, then provide relief from the symptoms. 

A flea allergy is best helped by giving all your pets an effective flea treatment, washing their bedding, and treating your house with a flea bomb. Be aware that fleas have become resistant to some flea treatments, so you may need to change brands.  

A food allergy can be managed by removing the ingredient from your pet’s diet. A dietary elimination trial is the main diagnostic method - it may take two to three months before you notice an improvement in your pet so it is important to persevere. 

A diet trial is usually done in one of two ways:

  • Novel protein diets - remove allergens like beef, chicken, or fish, and instead offer your pet a new protein that their immune system has never experienced and is therefore unlikely to react to. Common novel proteins include salmon, turkey, kangaroo, duck, and venison.
  • Hydrolysed protein diets - contain ingredients that have been broken down into the smallest possible molecular weight so that they do not elicit an immune response.

Avoid environmental allergens by keeping your backyard free of offending plants, walking your dog where there is no Tradescantia, and ensuring their bedding is cleaned regularly.

If your pet’s allergy symptoms are severe, we may also prescribe a medication to help, such as a medicated shampoo or cream for severe itching or an anti-inflammatory, antihistamine, or steroid to help settle the reaction. 

Pets, like people, can go into anaphylactic shock if they have a severe reaction to an allergen. This can be fatal if not treated immediately.

If your pet has a severe allergic reaction, please bring them to us immediately!



The above information is provided as an educational guide only and is not a substitute for advice from your pet’s healthcare professionals. If your pet’s symptoms continue, you are concerned about them or want further information, please don’t hesitate to contact us!

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