Allergies   VS Intollerance

A variety of dogs suffer from allergies or intolerance, but many pet owners are confused by the difference. So what is the difference between pet food allergies and intolerance?

Pet Food Allergies

A pet food allergy involves the immune system. This can be triggered by a dog’s response to a certain ingredient such as protein source. For example, cells may release histamine which causes itching.  Generally, food allergies cause skin-related issues in dogs such as inflammation, itching, hair loss and hot spots. There is also the possibility they can develop ear infections that can become a recurring theme once treatment has ended.

A dog that has a food allergy will most likely always suffer from this. However, the severity can change over time.

A common theme for owners is to assume that itchy skin is caused by a food allergy. However, true food allergies in dogs are very rare, making up for only 1% of all skin diseases in dogs.

Pet Food Intolerance

A pet food intolerance does not involve the immune system and is caused when a food doesn’t agree with a dog’s body. This is simply a functional or mechanical issue with digesting a particular food. For example your dog may be sensitive to wheat. Intolerances often mimic food allergies because the body can only demonstrate a problem in so many ways.

It can be challenging to identify what causes food intolerance. Owners can use an elimination diet to take away ingredients that they believe may be the cause of the problem. This works by removing a suspect ingredient for a minimum of 4 weeks from a dogs diet and then reintroducing the ingredient and wait for a return of any physical changes.

Common ingredients that may cause intolerance include grains (i.e wheat and maize), eggs, soya or dairy.

What can pet owners do?

If an owner believes that their pet is suffering from a food allergy or intolerance, there is a number of things they can do.

  1. Feed their pet hypoallergenic food as this helps to avoid common allergens and intolerances

  2. Choose a diet with a single protein source such as meat or fish

  3. Select a diet with novel ingredients

  4. Follow an elimination diet


Thankfully, food allergies in dogs are uncommon. Where they do occur, diagnosis and identification of the cause are difficult and time-consuming. With commercial testing services becoming more readily available, many owners are using these as a quick and simple way to find out what their pet is or may be allergic to.


However, what many pet owners and even veterinarians may not realise is that common commercial blood- and saliva-based allergy tests have not been validated – i.e. there is no evidence to say that a positive result obtained by these tests correspond to any actual clinical signs of food allergy/food intolerance in pets. Equally a negative result does not necessarily mean that an ingredient/food is fine for a pet.

A scientific study (1) published in 2019 found that saliva and blood tests for food allergies do not reliably distinguish between healthy dogs and those with food allergies. Over half (53%) of the healthy dogs showed weak positive reactions on the saliva test while 20-30% of the healthy dogs showed a strong positive reaction to certain food ingredients. Overall, there was no difference in the number of positive reactions to the tests between food-allergic and healthy dogs.

Another study (2) performed in 30 healthy dogs (with no evidence of food allergies) found that between 60-100% of the dogs tested positive for one or more of the foods/ingredients in saliva and blood tests. This highlights how easy it is for a test result to come back positive!

Key messages:

  • Saliva and blood tests for food allergies in dogs do not reliably distinguish between healthy and allergic dogs and should not be used for diagnosis of food allergy.

  • Blood and saliva allergy tests could result in the false identification of lots of common pet food ingredients as allergens.

  • This may push owners to avoid certain diets that include these ingredients when actually there is likely no need to avoid them.

  • Where a pet has shown a genuine adverse reaction to food it has eaten, details of ingredients to be avoided need to be taken seriously and the owner should be advised to consult a veterinarian.


1. Udraite Vovk L, Watson A, Dodds WJ, et al. (2019) Testing for food-specific antibodies in saliva and blood of food allergic and healthy dogs. Veterinary Journal; 245: 1-6.

2. Lam ATH, Johnson LN & Heinze CR. (2019) Assessment of the clinical accuracy of serum and saliva assays for identification of adverse food reaction in dogs without clinical signs of disease. Journal of the American Veterinary Medical Association; 255: 812-816