Allergies in Dogs and Cats

Terrier with severe atopy

Terrier with severe atopy

Just like people, dogs and cats can develop allergies when their immune system becomes ‘hypersensitive’ and recognises everyday, harmless particles as dangerous. The immune system then mounts an inflammatory response against these substances, manifesting as gastrointestinal upsets, respiratory irritation or skin problems such as itching, redness, scaling and hair loss. Virtually everything can potentially become an allergen and there are therefore many types of allergies.

 Flea hypersensitivity

One single flea is enough to make your pet very itchy if it has flea hypersensitivity. This is because flea saliva contains many allergens, which are injected directly into the blood when a flea takes a bite of your pet. It is therefore important to be vigilant with flea control even if you’ve never seen any fleas on your pet. There are many products on the market, including spot-ons and tablets. Treat all of your pets because fleas can jump from one animal to another. But treating you pets is only 5% of the job done. This is because 95% of the flea population, including eggs, larvae and pupae, live in the environment. Pay special attention to dark and cool areas and places that your pet rests and sleeps. Flea bombs alone are not sufficient as they cannot reach under solid furniture where it is perfect for flea larvae to hide.  Instead, use sprays specifically for fleas every 6 months to treat the environment.


Atopy is an allergy to environmental allergens such as pollen, moulds, insects and dust mites. They are often airborne and absorbed through the skin or the mucosa of the respiratory tract. It commonly causes itchy skin and sometimes respiratory signs such as asthma and nasal discharge. To diagnose atopy, other conditions such as skin parasites, flea and food allergies and hormonal diseases must first be excluded. This may include a skin scrape, flea treatment, food trial and blood tests. Once all the other differentials are ruled out, an intradermal test or a blood test (allergen specific IgE ELISA- dogs only) can then be performed to identify the allergens. Exposure to allergens in the environment should be minimised but complete avoidance is often difficult. Immunotherapy, sometimes called ‘allergy vaccine’, can be used to reprogramme the immune system to respond appropriately to the allergens in the environment. However, response to immunotherapy varies greatly and a complete cure is not always possible.

Contact allergy

Contact allergy commonly occurs on paws, muzzle, abdomen and sparsely haired areas where allergens can directly contact the skin. Common allergens include rubber, resins, cleaning products and cement. They can be identified by testing suspected allergens on bare or shaved skin. Once identified, contact with the allergen should be avoided either by removing the allergen or covering the skin with clothing or bootees.

 Food allergy

Dogs and cats with food allergies may suffer from diarrhoea as well as skin problems. There is no direct test for food allergies and the condition can only be diagnosed with an elimination diet. This involves feeding your pet a hypoallergenic diet, either a prescription or home cooked diet, for 6 weeks. As 90% of food allergies are caused by proteins, a home cooked diet should be made with a novel protein source e.g. kangaroo or rabbit with a suitable carbohydrate source, e.g. potato. Prescription diets such as Hill’s z/d diet contain hydrolysed proteins with particles so small that they are not surveyed by the immune system and therefore cannot cause an allergic reaction. The idea is to remove the offending food ingredient which is causing the allergy, and so remission of clinical signs should be observed at the end of the diet. The original food is then reintroduced for 2 weeks and recurrence of clinical signs confirms a diagnosis of food allergy.

Following diagnosis of food allergy, a food trial can be carried out to identify the food allergen. Add a food item each week to the prescription or home cooked diet to identify the ingredient that causes a relapse. By eliminating the food allergen from the pet’s diet, long term resolution can often be achieved.

Diagnosis and management of allergies are complicated and often challenging. Luckily there are many things that we can do to help your pet cope with their allergies. Apart from specific treatments for different kinds of allergies mentioned above, symptomatic treatment can help relieve discomfort and itchiness. These include antihistamines, steroids and immunosuppressive drugs.  Antibiotics are often warranted to treat secondary bacterial infections. Products that enhance the skin’s natural barrier such as fish oil supplements, shampoos (e.g. Allermyl) are also often useful. It is important to develop a plan that suits your pet to find the best solution for your pet’s allergies.