Updated October 11, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: An elimination diet trial is the only reliable way to diagnose food allergy in dogs and cats. Your pet eats only a prescription hydrolyzed diet or a carefully chosen novel-protein diet for about 8 weeks, with no other foods, treats, or flavored medications. If signs improve, you reintroduce the old food. If signs return, food allergy is confirmed.
Step 1: choose the diet with your vet
- Hydrolyzed diets: proteins broken into pieces too small to trigger the immune system
- Novel-protein diets: a protein your pet has never eaten
- Prescription diets are preferred because over-the-counter “limited ingredient” foods are often contaminated with other proteins
Step 2: feed only that diet for about 8 weeks
- No treats, table food, chews, or dental treats unless made from the same diet
- Ask your vet about unflavored versions of medications, including heartworm and flea preventives
- Tell everyone in the household
- Prevent access to other pets’ food, garbage, and hunting
Step 3: track signs
- Keep a weekly log of itching, ear problems, and stool
- Treat skin and ear infections during the trial so they don’t confuse results
Step 4: rechallenge
- If signs improve, feed the old diet again
- If signs return within about 2 weeks, food allergy is confirmed
- Your vet may then test single proteins to identify triggers
What to avoid
- Blood, saliva, or hair “food allergy tests,” which aren’t reliable
- Stopping the trial too early
Sources
- Olivry T, Mueller RS. Critically appraised topics on adverse food reactions of companion animals: duration of elimination diets. BMC Vet Res. 2015
- Mueller RS, Olivry T, Prélaud P. Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC Vet Res. 2016
- Merck Veterinary Manual: Food allergy in small animals
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.