Food Allergies in Dogs: The Only Way to Diagnose Them

True food allergies — or more precisely, adverse food reactions (AFR) — are one of the most mismanaged conditions in dogs. They're frequently diagnosed without proper testing, and equally frequently missed in dogs that actually have them. Here's what the evidence says.

What Are the Symptoms?

• Pruritus (itching) — often involving the paws, face, groin, armpits, and ears. May be non-seasonal or year-round.
• Recurrent ear infections — especially bilateral, repeatedly treated, repeatedly returning
• Skin lesions — hot spots, self-trauma, secondary bacterial or yeast infections
• Gastrointestinal signs — soft stools, increased frequency, mucus, occasionally vomiting
• Onset often in young dogs — though AFR can appear at any age

The Myths First

• ❌ Blood tests don't diagnose food allergy in dogs. IgE panels and hair analysis have no diagnostic validity. They produce impressive-looking lists and lead to unnecessary dietary restrictions.
• ❌ Skin prick tests don't work for food allergy in dogs.
• ✅ The only valid diagnostic test is the elimination diet trial.

The Elimination Diet Trial

An elimination diet feeds the dog only novel proteins and carbohydrates it has never eaten before — or a hydrolysed protein diet where proteins are broken into fragments too small to trigger an immune response.

1. Duration: 8–12 weeks minimum. Less than 8 weeks produces false negatives in a significant proportion of allergic dogs.
2. Strict adherence: no treats, no chews, no flavoured medications, no table scraps. One accidental exposure can invalidate the trial.
3. Novel protein options: kangaroo, venison, rabbit, crocodile — whatever the dog hasn't eaten before. Or a hydrolysed commercial diet.
4. Confirmation: if symptoms resolve, rechallenge with the original diet. Return of symptoms within days confirms the diagnosis. This step is often skipped, but it matters.

Most Common Culprits

Contrary to popular belief, the most common allergens are the most commonly eaten proteins: chicken, beef, dairy, and wheat — not the exotic ingredients. The novel protein principle exists precisely because novelty (not naturalness or grain-free status) is what matters.

After the Diagnosis

Once confirmed, the dog stays on the diet that controlled symptoms. Systematic rechallenge with individual ingredients can identify the specific culprit(s) — useful for choosing commercial foods. Lifelong management, but straightforward once the trigger is known.

Log your dog's diet history, symptoms, and flare patterns in Purzi. The date each food was introduced and when symptoms appeared or resolved is the core data that drives the diagnostic process.