Allergies in dogs and cats

Key information on allergies in pets
Written by Mayhew team
Updated 2 years ago

What are allergies? 

An allergy is defined as an abnormal bodily response to a usually harmless substance or ‘allergen’, for example a type of food or dust. Just like in humans, allergies in pets are manageable conditions, but are not curable. 

What are the signs of allergies in pets?

The most common signs of allergies in cats and dogs usually affect the skin and include symptoms such as itching and overgrooming. Occasionally allergies can cause respiratory symptoms such as coughing or sneezing (like people with hay fever). 

What are the most common causes of allergies in pets? 

 There are many causes of allergies in cats and dogs but some of the most common are:

  • Saliva of fleas 
  • Pollen, dust or other environmental allergens
  • Food

 Flea allergies 

Known as FAD, flea allergic dermatitis is thought to be the most common allergy in dogs and cats. All flea bites are itchy, however if your pet has an allergic reaction to flea saliva then it can cause extreme itchiness, hair loss and scabby patches of skin (typically around the flank, thigh, neck and ears). If left untreated, animals can go on to develop secondary skin infections caused by build-up of bacteria or yeast. 

Animals suffering from FAD are often extremely uncomfortable, itching, biting and scratching their skin. They will often have stained and broken fur where they have been overgrooming. 

Animals often first start to show signs of FAD in the summer, when flea populations are at their highest. Dogs and cats can develop FAD at any stage in their life, however it is very uncommon before the age of one.

Treatment of FAD can involve the use of medications such as steroids, but flea prevention is also vital. This can be done with a flea treatment medication supplied by your vet once the condition has been diagnosed; shop bought flea treatments are often not strong enough to kill the fleas. The skin itself may also need treating, for example if your pet has any secondary infections. 

Alongside treating your pet it is also important to treat your home for fleas, your vet will be able to advise you with the best products for this. Once the condition is under control, it is vital that your pet continues with regular flea treatments to prevent any flare ups in the future. 

Environmental allergies

Allergies to substances such as pollen or dust cause a condition known as ‘atopy’ which affects both cats and dogs. Environmental allergies can be categorised as either indoor (examples include dust mites and moulds) or outdoor (for example grasses and pollens).

This is similar to people with hay fever as levels of allergens in the environment can vary seasonally, although the symptoms are often quite different. The signs of atopy or ‘atopic dermatitis’ are actually closer to those of eczema in people, and include red, itchy and flaky skin. Often animals with atopy will be seen chewing at their feet at the skin in between their toes. 

It is possible to diagnose which substance your pet is allergic to in the environment by running allergy screening blood tests. Treatment for atopic dermatitis will be advised by your veterinary surgeon, but can include many different options such as steroids, topical creams and immunotherapy injections. 

Food allergies

Food allergies are estimated to be present in only 1-2% of dogs and less than 1% of cats. They are often confused with food intolerances, which is defined as an adverse reaction to an ingredient which does not involve the immune system (for example a tummy upset after eating a rich meal), which are much more commonly seen in pets. 

Clinical signs of a food allergy can be quite varied; however, the most commonly seen are itchy skin, inflammation and redness inside the ears, and gastrointestinal signs such as diarrhoea and weight loss. Secondary skin and ear infections are also common. Very rarely a food allergy can cause more serious signs such as asthma or anaphylaxis. 

The age at which most animals develop food allergies is between one to four years, however any animal can develop these allergies at any time. Certain dog breeds including German shepherds, French bulldogs, West Highland white terriers and Labrador retrievers are more likely than others to be affected. Common food allergens for both cats and dogs tend to be those that are more commonly fed, such as chicken and beef. Dairy is also a common allergen in dogs. 

Diagnosis of a food allergy is made via a dietary elimination trial that must be done safely under the direction of your vet. Treatment is based on exclusion of the allergen from your pet’s diet. 


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