Signs of food allergy

Merck notes that food allergy signs are similar to airborne allergies, "except there is little variation in the intensity of itching from one season to another."[2] Look for:

  • Itching, especially of the face, paws, ears, armpits and rear end
  • Repeated ear infections
  • Paw licking and red, stained fur between the toes
  • Skin infections that keep coming back
  • Sometimes soft stools, gas or vomiting

Not every itch is a food allergy

Many Frenchies with itchy skin actually have environmental allergies (pollen, dust mites), flea allergy, skin fold infections or mites. These need different treatment. Your vet will usually rule out fleas and infections before starting a food trial.

How food allergy is diagnosed

Merck explains that food allergies are diagnosed "by feeding a limited foodstuff (elimination or hydrolyzed) diet and seeing if the itching resolves."[2]

  1. Choose the trial food with your vet. Either a prescription hydrolyzed-protein diet, where proteins are broken down so small the immune system does not react, or a diet with a protein your dog has never eaten.
  2. Feed only that food. Merck stresses this includes "treats and anything the dog eats besides its regular food (including table food, flavored medications, and toothpaste)."[2]
  3. Keep going long enough. Merck says the trial diet "should be fed for up to 3 months."[2]
  4. Challenge. If itching improves, the old food is reintroduced. Signs usually return "between 1 hour and 14 days," which confirms the allergy.[2]

Why blood, saliva and hair tests do not work

Many companies sell at-home "food sensitivity" tests using blood, saliva or hair. Merck is clear: "Blood and skin tests are not reliable for diagnosis" of food allergy.[2] These tests can lead owners to cut out foods unnecessarily while missing the real cause.

Tips for a successful food trial

  • Tell everyone in the household, and visitors, not to give any other food.
  • Use pieces of the trial food as treats.
  • Ask your vet about unflavored versions of any medications.
  • Keep a weekly diary of itching on a 1 to 10 scale.
  • Pick up food bowls of other pets and keep trash secured.

Living with a food-allergic Frenchie

Once the trigger is found, most dogs do well on a diet that avoids it. Read labels carefully, since many foods contain several protein sources. If itching returns, see your vet: dogs can have more than one allergy at a time.

Sources and references

  1. O'Neill DG, Packer RMA, Francis P, Church DB, Brodbelt DC, Pegram C. French Bulldogs differ to other dogs in the UK in propensity for many common disorders: a VetCompass study. Canine Medicine and Genetics. 2021;8(1):13. doi:10.1186/s40575-021-00112-3.
  2. White SD, Moriello KA. Allergies in Dogs [Internet]. Merck Veterinary Manual; 2018 Jun [updated 2024 Sep; cited 2026 Nov 3].

Last reviewed November 3, 2026. Educational information only. This guide does not replace advice from your veterinarian.

Sources checked November 3, 2026. This guide has not been reviewed by a veterinarian and is not a substitute for veterinary advice.