Food Allergy in Dogs

Could your itchy dog have a “food allergy”? 

Could your dog that flaps its ears, shakes its head have a “food allergy”?


Food can be a flare factor or direct cause of itch (pruritus) in the dog. The term used for food allergy is adverse food reaction (AFR) as not all reactions are actually allergic.


Dogs with adverse food reaction usually have non-seasonal (not worse in summer or winter), constant itch. Often the itch will respond to treatment with corticosteroids in the early stages but they have less effect with time. The itchy dermatitis usually affects the EARS, feet, face, underarms (axilla), and around the BOTTOM (perineal and anal). Unfortunately this can be the same distribution as occurs in another itchy and often related condition, ATOPY. In atopy, animals are allergic to environmental allergens especially dust mite mould (Def1) and pollens. The areas affected in AFR are not the same as occurs in flea allergy dermatitis- this typically affects the base of tail most.


Food allergy can cause itchy or infected ears and no other signs in the dog!


Onset of AFR occurs at any age; including the very young. Not many other itchy conditions occur in less than 1 year old dogs making AFR the main differential diagnosis for itch in this group.  It can also turn up in old dogs- onset at 14 years old has been recorded.


The itch associated with AFR is usually intense from the onset, compared to many other itchy conditions like atopy and flea allergy that get progressively worse over time. Some dogs with AFR may have gastrointestinal signs as well like vomiting, mucoid diarrhoea, borborygami (grumbling tummy) and gas.


Remember, AFR can affect EARS ONLY. Some suggest involvement of the bottom (perineum- under the tail) in an itchy dog means AFR is likely.


AFR occurs because of specific molecules, in humans these have been identified as glycoproteins usually 10 to 70kd in size.

To diagnose AFR an elimination trial is required. Novel sources (one’s the dog have never eaten before) of protein & carbohydrate need to be fed for 6 to 10 weeks. If the itch stops, suspected food is reintroduced one ingredient at a time and if the reaction recurs AFR is confirmed, this is called provocative re-challenge. Finding a source of protein not previously eaten can be difficult, as can preparing the diet. There are commercial diets available like Hill’s z/d cans & biscuits. These contain proteins that have been denatured (hydrolysed), but with such commercial diets there are a percentage of animals that will still react. If the dog improves on z/d & relapses with re-challenge of old food then AFR is confirmed, however no improvement on z/d does NOT rule out AFR completely.

Itchy dogs often have more than one cause of dermatitis- atopy and AFR and flea allergy can occur in the same animal, then there are often secondary infections involved once the skin is irritated and damaged. A stepwise approach to eliminate possible causes is required. Treating the itch and not the cause can be frustrating and more expensive in the long run. 

Mac Kneipp