If your dog has been itching for months, or their stomach has never quite settled, somebody will eventually say the word allergy. And then somebody else will suggest a blood test, or a hair test, or a swab you post off in an envelope.
Here is the uncomfortable truth, and it is worth knowing before you spend any money: there is no blood test, saliva test or hair test that reliably diagnoses a food allergy in a dog. The only method that actually works is an elimination diet, also called an exclusion diet or a diet trial. It is free, it is slow, and it is almost entirely down to you.
This guide walks through how to run one properly.
What an elimination diet actually is
You feed your dog one protein they have never eaten before, and nothing else at all, for 8 to 12 weeks. If the symptoms improve, food was involved. If they do not, food probably was not, and you have saved yourself from chasing it any further.
That is the whole method. The difficulty is not in understanding it. The difficulty is in the words nothing else at all.
Before you start: talk to your vet
This is a diagnostic procedure, not a shopping decision. Book a conversation with your vet first, for three reasons.
- Itching has causes other than food. Fleas, mites, and environmental allergies such as pollen and house dust mite are all far more common than food allergy, and a diet trial will not touch any of them. Ruling those out first saves you three wasted months.
- Secondary skin and ear infections need treating alongside the trial, or the itching continues regardless of what is in the bowl and you cannot read the result.
- Puppies, pregnant dogs, seniors and dogs with existing medical conditions need the diet checking for nutritional adequacy before they go on it.
A vet may also suggest a hydrolysed prescription diet rather than a novel protein. Both are legitimate. The novel protein route described here is the one most owners can run at home with ordinary food.
Step 1: work out what your dog has already eaten
The whole method rests on finding a protein with no history. So before you choose anything, write down everything your dog has eaten in their life as far as you can remember. Every food, every treat, every dental stick, every training reward, every table scrap, every flavoured wormer.
Most UK dogs have eaten chicken, beef, lamb, salmon, turkey, duck, pork and white fish by the age of two, usually without the owner realising, because those proteins appear in almost every mainstream food and treat. That is precisely why they are the usual suspects. A sensitivity is a learned immune response, so it develops to things the body has met repeatedly, not to things it has never seen.
Check the ingredients panel on the bag you are currently feeding as well. Phrases like "meat and animal derivatives" or "with chicken" mean you genuinely do not know what is in there.
Step 2: choose a genuinely novel protein
Novel means new to your dog. For most British dogs, the realistic options are ostrich, kangaroo, horse, goat or venison.
Our single-protein range is built for exactly this job. Every Happy Dog Pure recipe is one named protein and nothing else, with no soy, no grain and no vegetable additives, which is the only way you can be certain what you are testing.
- Pure Kangaroo Wet Dog Food (Australia), 100% kangaroo, from £4.19 for a 400g tin. Naturally lean, and about as far from a British dog's usual diet as it is possible to get.
- Pure Ostrich Wet Dog Food (Africa), 100% ostrich, from £4.69 for 400g. Rarely eaten in the UK and low in fat.
- Pure Sensitive Horse Wet Dog Food (Montana), 100% horse, from £3.79 for 400g. This is usually where owners end up when chicken, beef, lamb and fish have all been tried already.
If your dog prefers dry food, or you want to feed both, the matching kibbles keep the diet to one protein throughout: Happy Dog Africa is ostrich (£8.29 for 1kg, £32.29 for 4kg, £64.69 for 12.5kg) and Happy Dog Montana is horse (£8.29 for 1kg, £59.19 for 10kg). Pairing a Pure tin with its matching kibble is the tidiest way to run a trial, because the protein in the bowl never changes.
A note on the two most common mistakes here. Fish is not novel for most dogs, because salmon and white fish are everywhere in "sensitive" foods. And "grain free" is not the same thing as novel protein. Grain-free chicken is still chicken, and chicken is far more likely to be the problem than wheat.
Step 3: buy a 1kg bag or a few tins first
Before you commit to a 12.5kg sack, buy the smallest size and find out whether your dog will actually eat it. Ostrich, horse and kangaroo taste different to what they are used to, and a small number of dogs turn their nose up at the first bowl. Every Happy Dog Pure recipe is available as a single 400g tin, and every dry recipe comes in a 1kg bag, precisely so you can test before you stock up.
Once you know they will eat it, buy enough for the whole trial in one go. Running out in week six and feeding "just a few days" of something else resets the clock.
Step 4: transition over about a week
Swap gradually across roughly seven days, mixing a little more of the new food in each day. A slow change is kinder to a stomach that is already unhappy, and it makes any reaction easier to attribute to the right thing.
Loose stools during the changeover are common and are not, on their own, evidence that the new food has failed. Give it the week.
Step 5: the 8 to 12 weeks. This is where trials fail
From the first full day of the new food, your dog eats that food and drinks water. That is the entire list.
The things that quietly break a trial, in roughly the order they happen:
- Treats. Every single one. Training treats, dental chews, the biscuit at the groomer, the corner of toast.
- Other people. Tell everyone in the house, and anyone who walks the dog or looks after them. One well-meaning grandparent with a bit of ham can cost you eight weeks.
- Flavoured medication. Many wormers, joint supplements and flea tablets are flavoured with chicken or beef liver. Ask your vet for unflavoured versions for the duration.
- Flavoured toothpaste. Same problem, same solution.
- Other animals' bowls. The cat's food is the single most common hidden variable in a multi-pet house. Feed separately, and lift the bowl afterwards.
- Walks. Dogs who scavenge need a lead and, if necessary, a basket muzzle for three months. It is not forever.
If you need something to reward your dog with, use a portion of their trial food. Dry kibble works as training treats straight from the bag. Wet food can be spread thinly and baked into small pieces, or simply spooned onto a mat and licked off. It counts as part of the day's ration, not as an extra.
Keep a diary. A line a day is enough: what went in, how the stools looked, how much scratching you noticed, whether the ears were bothering them. Itching improves gradually and memory is unreliable, so without notes you will genuinely not be able to tell in week ten whether things are better than week two.
Step 6: reading the result
Skin takes longer to respond than the gut. Digestive symptoms often settle inside two to three weeks. Itching and ear inflammation can take the full 8 to 12 weeks, because the skin has to recover from months of irritation.
Three broad outcomes:
- Clear improvement. Food is involved. Go to step 7.
- Some improvement, not enough. Common when there is both a food component and an environmental one, such as pollen alongside a protein sensitivity. Worth discussing with your vet rather than abandoning.
- No change at all, with the rules genuinely kept. Food is very probably not the cause. That is a useful answer, not a failed experiment, because it stops you changing the food every six weeks for the next two years.
Be honest with yourself about whether the rules were kept. A trial with three slip-ups in it tells you nothing either way.
Step 7: the challenge, which most people skip
If your dog improved, you have not yet learned which protein was the problem. You have only learned that one particular diet suits them.
The way to find out is to reintroduce the old foods, one at a time, and wait. Add a single protein back, keep everything else identical, and give it up to two weeks. If symptoms return, that protein goes on the avoid list and you return to the trial food until things settle again. Then test the next one.
It is tedious, and it involves deliberately making your dog itchy again, which nobody enjoys. But the alternative is a lifetime of avoiding eleven foods when only one of them was ever the culprit, which makes everything from choosing a treat to boarding your dog harder than it needs to be.
Plenty of owners decide not to challenge at all, and simply stay on the food that works. That is a completely reasonable decision, as long as the food is complete and balanced for long-term feeding. Every Happy Dog Pure recipe is.
Frequently asked questions
How long does a dog elimination diet take?
Between 8 and 12 weeks for the trial itself, plus around a week to transition onto the food. Digestive symptoms often improve within two to three weeks, but skin and ear symptoms usually need the full period. Adding the reintroduction challenges afterwards can take a further two to three months.
Can I use a grain-free food instead?
No. Grain is rarely the trigger. True food allergies in dogs are usually to a protein, most often beef, chicken or dairy. A grain-free chicken recipe still contains the most common culprit.
What can my dog have as treats during the trial?
Only their trial food. Use kibble from the bag as training rewards, or a spoon of the wet food, counted as part of the daily ration. No chews, no dental sticks, no human food.
Do hair or blood allergy tests work for dogs?
Not for food allergy. Published studies have found that these tests return positive results for foods the dog has never eaten, and even for samples taken from stuffed toys and distilled water. Veterinary dermatology guidance is consistent on this point: the elimination diet is the diagnostic standard.
Is ostrich or kangaroo actually better for dogs?
Not nutritionally. They are useful specifically because they are unfamiliar. A protein your dog has never encountered gives the immune system nothing to react to, which is the entire basis of the method.
My dog will not eat the new food. What now?
Try a different novel protein rather than adding anything to make the current one tastier, because anything you add becomes part of the test. Warming wet food to room temperature usually helps, as does mixing a little of the matching wet recipe through the dry.
Can I run a trial on a puppy?
Only with your vet's guidance. Growing dogs have specific nutritional requirements and a restricted diet needs checking for adequacy before it starts.
Where to start
If you are ready to begin, pick one protein your dog has never eaten and buy the smallest size to test acceptance. The full single-protein range sits in Wet Dog Food and Dry Dog Food.
If you are still working out whether food is the problem at all, start with our guide to the best dog food for itchy skin in the UK, or, if the trouble is at the other end, the best dog food for sensitive stomachs. If you are weighing up tins against kibble more generally, wet versus dry dog food covers the trade-offs.
Free UK delivery on orders over £30.
This article is general information, not veterinary advice. Always speak to your own vet before starting a diet trial, particularly if your dog is a puppy, is pregnant, is elderly, or has an existing medical condition.