Your dog is itching. Your vet mentioned a possible food allergy. You've started Googling and now you're deep in a rabbit hole of "food allergy vs food sensitivity vs food intolerance" and none of the explanations quite agree with each other.
Here's the practical version — what the terms actually mean, why the distinction matters for how you investigate, and what symptoms to watch for in each case.
The most important takeaway upfront: whether your dog has an allergy or a sensitivity, the diagnosis method is the same — a strict elimination diet with careful tracking. No blood test, saliva test, or hair test can reliably diagnose either one in dogs. The mechanism differs. The path to finding the answer doesn't.
The Three Categories of Adverse Food Reactions in Dogs
Veterinary dermatologists use the umbrella term "adverse food reaction" (AFR) to cover all forms of abnormal response to food, then subdivide based on mechanism:
1. True Food Allergy (IgE-Mediated)
A true food allergy involves the immune system's IgE antibodies. On first exposure to an allergen, the immune system produces IgE antibodies specific to that food protein. On subsequent exposures, these antibodies trigger mast cells to release histamine and other inflammatory mediators — producing the classic immediate allergy response.
In dogs, true IgE-mediated food allergy can produce:
- Rapid-onset facial swelling or hives (urticaria) — typically within minutes to two hours of eating
- Vomiting or diarrhoea starting soon after a meal
- In severe cases, anaphylaxis — a dangerous, life-threatening reaction requiring emergency veterinary care
Genuine anaphylaxis from food is rare in dogs, but it exists. If your dog ever develops sudden facial swelling, collapses, has difficulty breathing, or shows extreme distress shortly after eating, treat it as an emergency.
The critical point: true IgE-mediated food allergy is uncommon in dogs. It represents a minority of adverse food reactions. Most dogs with food-related symptoms have one of the categories below.
2. Food Sensitivity (Non-IgE Immune Reaction)
Food sensitivity — sometimes called food hypersensitivity in veterinary literature — involves immune mechanisms other than IgE. T-cell mediated reactions, IgG antibody responses, and other inflammatory pathways drive a slower, sustained inflammatory process that doesn't produce the dramatic acute allergy symptoms.
This is by far the most common form of adverse food reaction in dogs. Reactions are:
- Delayed — typically appearing 3–7 days after exposure, not immediately
- Chronic — the symptoms persist as long as the trigger food is in the diet
- Systemic — affecting primarily the skin and ears, sometimes the gut
- Cumulative — small amounts may be tolerated short-term; daily exposure over weeks produces clear symptoms
Because there's no immediate reaction to observe, food sensitivity is extremely difficult to identify without systematic tracking. The owner feeds chicken every day, the dog itches every day, and the connection remains invisible — because everyone is looking for a sudden change that never comes. Humans experience the same invisible pattern — learn more about food sensitivities in humans.
3. Food Intolerance (Non-Immune)
Food intolerance doesn't involve the immune system at all. It's a digestive problem — the inability to properly process a specific food component, usually because of enzyme deficiency or direct chemical irritation.
The classic example in dogs is lactose intolerance: insufficient lactase enzyme means lactose isn't broken down, bacteria ferment it in the gut, and digestive symptoms follow — gas, loose stools, discomfort. No immune activation, no skin symptoms.
Other examples include reactions to high-fat foods that can trigger pancreatitis in susceptible dogs, sensitivity to food additives or preservatives, and intolerance to certain fibre types.
Food intolerance typically produces primarily gut symptoms. If your dog has skin symptoms alongside digestive issues, a food sensitivity rather than a simple intolerance is the more likely mechanism.
Why the Distinction Matters in Practice
For diagnosis purposes, the mechanism matters less than you might think — because the elimination diet is the gold standard for all three categories. But the distinction helps you understand:
How quickly to expect a reaction during reintroduction. If testing a reintroduced food, an IgE-mediated allergy might produce symptoms within hours. A food sensitivity reaction might take 5–7 days of daily feeding before symptoms appear. Food intolerance reactions are usually seen within 24–48 hours and are primarily digestive.
If you reintroduce a food for three days, see no change, and conclude it's safe — but your dog actually has a sensitivity — you've drawn a false conclusion. One to two weeks of daily feeding per reintroduced food is the recommended testing period.
Whether blood allergy testing is useful. Serum IgE testing in dogs has been studied for environmental allergens and has moderate reliability in that context. For food allergens, serum IgE testing — and all other blood, saliva, and hair tests — has been shown in multiple independent studies to be unreliable. The tests cannot accurately distinguish between clinical food sensitivity and normal immune exposure to food proteins. This is why veterinary dermatology guidelines consistently recommend against using these tests for food sensitivity diagnosis.
The Symptoms: What Food Reactions Look Like in Dogs
One of the most important things to understand about food reactions in dogs is that the skin speaks first, and loudest. Unlike food reactions in humans, which often manifest primarily as gut symptoms, dogs show adverse food reactions predominantly through their skin and ears.
Primary Skin Symptoms
Constant itching and scratching — typically not seasonal. Dogs with food sensitivity scratch year-round, in all weather, in all environments.
Ear inflammation and infections — recurring otitis externa, often with dark, waxy or greasy discharge, strong odour, head shaking, and pawing at ears. The "ears and rears" pattern — simultaneous ear and perianal symptoms — is particularly associated with food reactions.
Paw licking and chewing — persistent licking of the paws, especially between the toes, producing rust-coloured staining from saliva.
Facial rubbing — rubbing the face on furniture, carpets, or against legs. Redness or inflammation around the muzzle, chin, or eyes.
Red, inflamed skin — especially in skin folds, the groin, armpits, and around the tail base.
Secondary yeast (Malassezia) overgrowth — identifiable by the characteristic musty or "corn chip" odour, greasy skin texture, and thickened, hyperpigmented skin in chronic cases.
Hot spots — acute, moist dermatitis triggered by self-trauma from scratching or licking.
Recurring bacterial skin infections (pyoderma) — circular lesions with scaling edges, papules, and hair loss.
Gut Symptoms
Gut symptoms are less prominent than skin symptoms in food-reactive dogs, but they occur in roughly 10–30% of cases:
- Soft stools, loose stools, or intermittent diarrhoea
- Increased frequency of bowel movements
- Gas and bloating
- Vomiting — particularly if it occurs consistently after meals
- Mucus in stools
Behavioural and General Signs
- Restlessness and difficulty settling, especially at night
- Irritability or changes in temperament
- Reduced energy or enthusiasm for play
- Scooting — dragging the rear end along the ground
The Timing Pattern That Reveals Everything
The key to identifying a food reaction in your dog is the timing — and this is where tracking becomes essential.
In a dog with food sensitivity, the pattern typically looks like this over a week:
- Day 1: Dog eats trigger protein
- Days 2–3: No obvious change
- Days 4–6: Scratching increases, ears may feel warmer, paw licking intensifies
- Day 7: Owner notices dog "having a bad week" — but the trigger protein was eaten six days ago and has been forgotten
Multiply this over months of daily exposure, and the connection between food and symptoms becomes completely invisible to unaided observation.
This is why tracking works and guessing doesn't. A daily log of food and symptoms, maintained consistently for 8–12 weeks, captures the delay.
When to See a Vet Immediately
Some symptoms require veterinary attention urgently:
- Any sudden-onset swelling of the face, muzzle, or throat
- Hives that appear within minutes to an hour of eating
- Collapse, extreme weakness, or loss of consciousness after eating
- Difficulty breathing
- Persistent vomiting that prevents the dog from keeping water down
- Bloody diarrhoea
A Practical First Step
If your dog has chronic skin or ear symptoms and you suspect food is involved:
- Speak to your vet. Rule out parasites, active infections, and consider a dermatology referral.
- Don't rely on commercial food sensitivity tests. Blood, saliva, and hair tests for food sensitivity in dogs are not validated.
- Start a food diary now. Even before a formal elimination trial, logging food and symptoms daily will reveal patterns.
- Consider a structured elimination diet trial with your vet's guidance. Choose a novel protein your dog has never eaten.
Data Sources
- Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC Vet Res. 2016;12:9.
- Mueller RS, Olivry T. Critically appraised topic on adverse food reactions of companion animals (4): can we diagnose adverse food reactions in dogs and cats with serum IgE and IgG? BMC Vet Res. 2017;13:275.
- Olivry T, et al. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Vet Res. 2015;11:225.
- Tham HL. Elimination Diet Trials: Steps for Success and Common Mistakes. Today's Veterinary Practice. 2024.
- Hensel P, et al. Canine atopic dermatitis: detailed guidelines for diagnosis and allergen identification. BMC Vet Res. 2015;11:196.
- Verlinden A, et al. Food hypersensitivity reactions in dogs and cats: a review. Crit Rev Food Sci Nutr. 2006;46(3):259–273.
- Purina Institute. Diet Elimination Trials. [Serum, saliva, and hair allergy testing are not reliable in dogs and cats.]
- Pali-Schöll I, et al. Immediate type hypersensitivity reactions to food are less frequently diagnosed in companion animals than in humans. Allergy. 2017;72(12):1823–1835.
Disclaimer: This article is for educational purposes only and does not constitute veterinary advice. Always consult with a qualified veterinarian before changing your dog's diet or stopping any prescribed treatments. If your dog displays any sudden-onset symptoms such as facial swelling, hives, collapse, or difficulty breathing after eating, seek emergency veterinary care immediately.