The Canine Ledger

Food Allergy or Environmental? Why Blood, Saliva and Hair Tests Don't Tell You

A hair and saliva allergy test couldn't tell an allergic dog from a healthy one, or from fake fur. What the evidence says works instead.

Written by thecanineledger

In 2019, two veterinary dermatologists sent a commercial allergy-testing company some samples. There were ten sets of fur and saliva samples from a dog known to have allergies and a healthy dog with none. There were also five samples of fake fur, from a toy, sent with water instead of saliva.

The company tested them for 128 food and environmental allergens and sent back results for all of them. The researchers found that “The distribution of test results from samples obtained from allergic, non-allergic or fake dogs was not different from that expected due to random chance” (Coyner & Schick, J Small Anim Pract 2019). Repeat samples from the same dog didn’t give consistent results either: the study rated the test’s repeatability as “poor to slight.”

Their conclusion: “Hair and saliva testing should not be used to diagnose allergies and is not a substitute for veterinary-directed allergy evaluation and diagnostics.”

While it was one small study of one company’s test, it went to the heart of the problem. These tests promise to tell you what your dog is allergic to, from a few hairs, and there is no good evidence that they can. This page explains what the evidence does support.

1. Why the tests appeal

They are easy and cheap compared with the alternative. An itchy dog is miserable, and so is their owner. A test that arrives in the post and gives a list of foods to avoid sounds like an answer.

The alternative, a strict elimination diet, takes weeks and is hard to stick to. The systematic review we cite below starts from exactly that point, noting that diet trials “are inconvenient and client compliance can be low.” The tests sell because the real method is difficult.

2. Hair and saliva tests

Coyner and Schick’s study is the only one we found that tested a hair and saliva kit directly. The authors note that the companies selling such tests “provide no validation of test accuracy.” In other words, they don’t publish evidence that the test works.

The study was small: two real dogs and a toy, sent to one company. It can’t prove that every hair or saliva test is useless. It does show that the one tested couldn’t tell a dog from fake fur, and that the burden of proof sits with the companies, who haven’t met it.

Our note: Coyner and Schick is the only study we found that tested a hair and saliva kit directly.

3. Blood tests for food allergy

Blood tests are different. They are done through vets and measure real antibodies. For food allergy, though, the evidence is still poor.

A systematic review of every test for food allergy in dogs and cats, published in 2017, looked at blood tests for two kinds of antibody, IgE and IgG, alongside skin tests, patch tests and others (Mueller & Olivry, BMC Vet Res 2017). It concluded:

“Testing for serum food-specific IgE and IgG showed low repeatability and, in dogs, a highly variable accuracy.”

“Low repeatability” means the same sample can give different results on different runs. “Highly variable accuracy” means it can’t be trusted to tell an allergic dog from one that isn’t. The review’s bottom line was that “the best diagnostic procedure to identify AFRs in small animals remains an elimination diet with subsequent provocation trials.” AFR stands for adverse food reaction.

One test did show promise: a patch test, where food is held against the skin. The review said a negative result “could enable a choice of ingredients for the elimination diet in selected patients.” That’s a help in choosing a diet, not a replacement for one.

Our note: The CAT 4 review is from 2017. Two newer studies agree with it. A 2026 systematic review of 59 studies found that “Serological IgG/IgE (and salivary) tests were poorly correlated with clinical outcome”. It concluded that “No alternative test reliably replaces EDT+OFC”, meaning an elimination diet followed by a food challenge. It rated the patch test best of the skin tests, but said its practical value is limited (Morales-Romero et al., J Am Vet Med Assoc 2026). A 2026 study of 12 dogs found that the performance of blood IgE, prick and patch tests for food “was poor” (Sofou et al., Vet Dermatol 2026). We could read only the abstracts of both.

4. Blood and skin tests for environmental allergy

For environmental allergies, such as dust mites and pollens, allergy tests do have a proper use. It just isn’t diagnosis.

The international committee of veterinary dermatologists says that both skin tests and blood tests “are not recommended as screening tests and should only be used to confirm the clinical diagnosis of canine AD” (Hensel et al., BMC Vet Res 2015). AD is atopic dermatitis.

The Merck Veterinary Manual explains why. Allergy testing measures antibodies, but “alone, allergy testing is not diagnostic but rather reflects exposure” (Merck, Atopic Dermatitis in Dogs). A dog can show a reaction to something on a test without that being what makes them itch.

So vets diagnose atopic dermatitis first, from the dog’s history and examination and by ruling out other causes. Only then do the tests come in. Merck says “The primary reason to pursue intradermal or serological allergy testing is to identify the offending allergens in an individual animal and to formulate allergen-specific immunotherapy.” That is a treatment made up from the specific things a dog reacts to. Even then, Merck adds, “Test results are important only if the offending allergens identified are compatible with the history or seasonality of pruritus.”

5. What does work: the elimination diet

For food allergy, the answer hasn’t changed in years. It is a strict diet trial, then a challenge with the old food.

The 2015 treatment guidelines say “An 8-week restriction-provocation dietary trial should permit the diagnosis of food allergy in most dogs” (Olivry et al., BMC Vet Res 2015). Why eight? A separate review found that by five weeks more than 80% of dogs with food allergy had improved, and that “Increasing the diet trial duration to 8 weeks leads to a complete remission in more than 90 % of dogs and cats” (Olivry, Mueller & Prélaud, BMC Vet Res 2015).

Then comes the part people skip. Once the itch has settled, the old food goes back in. If the itch returns, food is the likely cause. If it doesn’t, the improvement may have been something else, such as a change of season.

How long to wait? A review of nine studies found that half of food-allergic dogs flared within five days of the old food going back in, and 90% within 14 days. Its conclusion was that vets “need to wait for 14 and 7 days for more than 90% of dogs and cats with a skin-manifesting FA to have a flare of clinical signs, respectively” (Olivry & Mueller, BMC Vet Res 2020). FA is food allergy. For dogs, that’s two weeks.

Use a diet your vet chooses. The diet must contain proteins your dog hasn’t eaten before, or proteins broken down so the immune system doesn’t recognise them. Ask your vet which one. → The Itchy Dog: Allergies, Atopic Dermatitis, and What Actually Helps

6. If you’ve already done a hair or saliva test

That’s all right. Lots of people have. The test won’t have harmed your dog.

Don’t rely on the results. Avoid the trap of cutting out a long list of foods. It makes a proper diet trial harder later, and can leave a home-made or restricted diet unbalanced. → Why Most Homemade Dog Food Isn’t Complete

Take your dog to the vet instead, and mention that you’ve done the test. The work-up for an itchy dog starts with fleas, mites and infections, not with allergies.

Our note: The test itself is harmless. Cutting foods on its results could cause problems.

7. What we could not verify

Commonly saidWhat we found
“A hair or saliva test shows what my dog is allergic to”No evidence it can. In one study, a test gave results for fake fur no different from chance.
“A blood test can diagnose food allergy”Not reliably. A systematic review found low repeatability and highly variable accuracy in dogs.
“An allergy test diagnoses atopic dermatitis”No. Tests are used after diagnosis, to choose immunotherapy. Merck: testing “reflects exposure.”
“A few weeks on a new food is enough”Eight weeks is the guideline. More than 90% of food-allergic dogs settle by then.
“These tests are validated”The companies haven’t published evidence. Coyner & Schick: the companies “provide no validation of test accuracy.”

Sources

Always confirm with your vet before acting on anything on this page.