Food-induced hypersensitivity reactions are an important cause of cutaneous signs, especially pruritus, in cats and dogs.
Etiology and Pathophysiology of Cutaneous Food Allergy
Hypersensitivity reactions are manifestations of an exaggerated immune response to otherwise innocuous items that should be tolerated. In the case of food allergies, the allergen is a component of the patient's diet (see the table Sources of Food Allergens in Dogs and Cats). In dogs, the most common food allergens are beef, dairy products, chicken, wheat, and lamb. In cats, the most common food allergens are beef, fish, and chicken. Food allergens can be found not only in commercially available diets or table food but also in less obvious sources, such as flavored medications, supplements, and treats.
It is unknown why food allergens trigger cutaneous signs.
Sources of Food Allergens in Dogs and Cats
Species | Common Food Allergens | Less Common Food Allergens |
|---|---|---|
Dogs | Beef, dairy products, chicken, wheat, lamb | Soy, corn, egg, pork, fish, rice |
Cats | Beef, fish, chicken | Wheat, corn, dairy products, lamb |
In addition to true hypersensitivity reactions (IgE mediated or otherwise), food-induced diseases can be categorized as follows:
metabolic syndromes (eg, lactose intolerance in humans and small animals)
pharmacological reactions (eg, GI and neurological disturbances after ingestion of methylxanthines in chocolate or hypoglycemia after ingestion of xylitol)
toxic reactions (eg, reactions to mycotoxins, renal failure from exposure to melamine in pet foods or from exposure to tartaric acid and potassium bitartrate in grapes)
Together, these conditions are broadly characterized as "adverse food reactions."
Food allergies have been best characterized in small animals. Although it is likely that large herbivores also have spontaneous food-induced hypersensitivity reactions, identification of food allergy in large animals is complicated by the difficulties associated with completely controlling food intake in animals not housed in confinement.
Some information is available about cutaneous food allergies in horses; however, most of it is anecdotal material presented in book chapters. A very small number of individual case reports describing food allergy in horses have been published in reviewed journals (1, 2).
Epidemiology of Cutaneous Food Allergy
A literature review of 28 high-quality manuscripts found that the reported prevalence of food allergy varied depending on the specific population evaluated (3). For example, 1–2% of dogs and < 1% of cats receiving any form of veterinary care were found to have some form of food allergy. This percentage increased considerably in pets with any form of dermatitis (0–24% of dogs; 3–6% of cats) or pruritus (9–40% of dogs; 12–21% of cats).
The most common food allergens often correspond with the most commonly fed food sources. Therefore, they vary somewhat depending on geographical differences in food sources and current feeding trends. A review of manuscripts published worldwide listed the most common food allergens reported in dogs and cats (see the table Sources of Food Allergens in Dogs and Cats) (4).
Animals can demonstrate hypersensitivity to more than one food source.
In contrast to environmental allergen–associated atopic dermatitis (in which most patients initially demonstrate clinical signs at 1–3 years old), the age of onset of food allergy is highly variable. Although both cats and dogs with food allergy typically also develop clinical signs in young adulthood (1–4 years old), the age of onset in dogs has been reported to range from < 6 months to 13 years, and in cats, from 4 months to 15 years. Thus, food allergy might be a particularly likely differential diagnosis in patients that initially develop skin disease at either a very young or a very advanced age (5).
There does not appear to be a clear sex-related predisposition to food allergy in either cats or dogs.
Breed predispositions to food allergy vary somewhat, depending on local breed prevalence. In most Western countries, however, German Shepherd Dogs, Labrador Retrievers, French Bulldogs, and West Highland White Terriers appear to be overrepresented. There is no clear breed predisposition to food allergy in cats (5, 6).
Clinical Findings of Cutaneous Food Allergy
The clinical signs associated with food allergy are highly variable.
The most commonly reported cutaneous clinical sign in dogs is pruritus (see dog images).
Courtesy of the LSU School of Veterinary Medicine Dermatology, Ear and Allergy Service.
In dogs, the distribution of pruritus can be focal, multifocal, or generalized. Areas typically affected include the pinnae, feet, ventrum, and (less commonly) perianal and perigenital skin. In dogs, pruritus associated with food allergy can be as severe as that caused by scabies (5).
Other common signs of food allergy in dogs include otitis externa (with or without secondary infection) and relapsing infections by Staphylococcus spp or Malassezia. Secondary infections can even occur in patients with food allergy that are pruritus-free when infections are controlled.
Less common cutaneous manifestations of food allergy include urticaria, angioedema, or pyotraumatic dermatitis.
As in dogs, the most common clinical sign associated with food allergy in cats is pruritus, which can manifest as scratching, rubbing, or self-removal of fur (self-inflicted alopecia).
Pruritus of the face, ears, and neck is very common in cats with food allergy (see cat image); pruritus can also occur on the ventrum, feet, or in a more generalized distribution.
Courtesy of the LSU School of Veterinary Medicine Dermatology, Ear and Allergy Service.
Other signs of food allergy in cats include lesions of the eosinophilic granuloma complex, miliary dermatitis, nonpruritic cutaneous nodules, and plasma cell pododermatitis (5, 6).
Both dogs and cats can simultaneously demonstrate both cutaneous and noncutaneous signs of food allergy. GI disease is the most frequently reported comorbidity. Although GI signs can include obvious abnormalities such as vomiting and diarrhea, more subtle signs include increased frequency of defecation (> 3 times per day); soft, formed stool; tenesmus; flatulence; and borborygmus. Patients can demonstrate varying degrees of weight loss.
Less commonly reported comorbidities of food allergy include anaphylaxis, asthma or respiratory distress, conjunctivitis, hypersalivation, hyperactivity, and nasal discharge (7).
Regardless of the appearance, clinical signs of food allergy are typically nonseasonal. However, waxing and waning disease can occur in patients not consistently receiving the same diet. Nonseasonal signs with seasonal exacerbations can occur in patients with both food allergy and environmental allergen–induced atopic dermatitis.
Diagnosis of Cutaneous Food Allergy
Dietary elimination trial
For diagnosis of food allergies in dogs and cats, dietary elimination trials remain the reference standard (8).
Other diagnostic tests include Western blot–based serological analysis, analysis of salivary IgA and IgM, and patch or combined patch and prick testing (9, 10, 11). Numerous other diagnostic methods have been investigated (and in some cases marketed), including ELISA-based serological testing to detect anti-food IgE, intradermal testing, and hair analysis. However, none of these methods reliably give consistently accurate results (ie, correlation with clinical reactivity).
One study evaluating the efficacy of a commercially available Western blot serological assay for canine IgE against certain foods found that the assay can help identify some foods that the patient does not tolerate (and thus should be avoided in dietary elimination trials); however, negative results did not necessarily correlate with clinical tolerance (12).
A study incorporating quantification of putative food-specific serum IgE, salivary IgA, and salivary IgM found that none of these modalities were consistently able to prove or disprove clinical food allergy in naturally allergic dogs, or to distinguish food-allergic dogs from healthy laboratory dogs (11).
Patch testing with raw and cooked food extracts has also been demonstrated to aid in the selection of foods for a potential elimination diet (13). In this case, negative results typically correspond to foods that the patient does not tolerate (and thus can be selected for use in dietary elimination trials); however, positive results were not necessarily associated with clinical intolerance. A related study using a combination of patch and prick testing demonstrated greater specificity (80%) than analysis of either modality on its own (10).
Western blot assay and patch testing can aid in the selection of an elimination diet, but neither technique on its own is sufficient to diagnose food allergy. Similarly, although the results of combined patch and prick testing can help to guide the selection of foods suitable for use in dietary elimination trials and food challenges, they are unlikely to be of use as stand-alone diagnostic tests.
Dietary Elimination Trials to Diagnose Cutaneous Food Allergy
Food allergy dietary elimination trials are typically conducted using novel protein diets (whether commercially available or home-cooked), hydrolyzed diets, diets containing both novel and hydrolyzed proteins, or elemental diets.
Novel protein diets must be carefully selected to avoid previously fed ingredients. The selection of an appropriate novel protein can be complicated by the potential for allergenic cross-reactivity. Thus, it might be prudent to avoid selecting diets that contain species similar to those previously fed (eg, lamb in diets for patients previously fed beef or milk).
Some experimental evidence suggests serological cross-reactivity between chicken, whitefish, and salmon (14). A moderate to marked similarity in the amino acid sequence for several common allergenic proteins has been demonstrated, between meat sources as disparate as chicken, alligator, horse, and rabbit. Although these results suggest the possibility of cross-reactivity, the clinical relevance of these findings is not yet clear (15).
In hydrolyzed diets, the constituent proteins are broken into smaller fragments, which are more difficult for the immune system to detect and react to. These diets can be categorized as partially hydrolyzed (generally < 5 kilodaltons) or extensively hydrolyzed (generally < 3 kilodaltons, but some extensively hydrolyzed diets are broken into fragments of ≤ 1 kilodalton).
Partially hydrolyzed diets might be broken down enough that they are tolerable to an animal sensitized to their source protein; however, some sensitized animals still react to these diets. Extensively hydrolyzed diets are less likely to cause clinically appreciable food allergy responses, even in animals sensitized to their source protein.
Elemental diets incorporate a mixture of synthetic amino acids to meet the patient's protein requirements. The likelihood of clinically appreciable food allergy responses to these diets is generally expected to be extremely low, but not zero.
For diagnosing food allergy, ultrahydrolyzed and elemental diets might be better suited than diets incorporating partially hydrolyzed proteins. However, once the diagnosis has been made, patients can be evaluated to determine whether they will tolerate a partially hydrolyzed or novel protein diet.
Regardless of the diet format chosen for a dietary elimination trial, the patient should be fed that diet exclusively for the whole trial period. Recommendations for the duration of elimination diets vary. A literature review found that a minimum of 10 weeks might be required to identify 95% of food-allergic patients (16).
The duration of an elimination diet might be able to be shortened to as few as 4 weeks if the diet is started concurrently with a 2- to 3-week course of prednisolone at anti-inflammatory doses (17, 18). Patients demonstrating relapse upon steroid withdrawal can be placed back on prednisolone for a longer period before the next attempt at discontinuation.
Shortening the duration of the diet trial might increase pet owner compliance.
Potential Pitfalls of Elimination Diets to Diagnose Cutaneous Food Allergy
Although the selection of an appropriate elimination diet is critical for diagnosing food allergy, the elimination of other sources of food proteins is equally important. Clients should be made aware that any food-based item must be avoided, including rawhide chews, pill pockets, table food, flavored vitamin and mineral supplements, some oral arthritis supplements, and flavored toys.
Pearls & Pitfalls
|
During a dietary elimination trial, either patients should be fed separately from other animals in the house, or all animals should be fed the same diet. There is also potential for cross-contamination if pets share a water bowl. Patients with a tendency to eat the feces of other animals should be prevented from doing so.
Chewable or flavored heartworm preventatives or flea medications generally contain beef, pork, or soy protein, regardless of whether this ingredient is listed on the label. Unflavored, injectable, or topical products should be used instead.
Medication capsules might be made of beef or pork gelatin. If medications in capsule form must be given, it might be optimal to have the client open the capsule and empty the contents onto the patient's food.
Miscellaneous Considerations for Diagnosis of Cutaneous Food Allergy
Secondary infections (by Staphylococcus spp or Malassezia) are common in food-allergic patients, and the discomfort associated with these conditions can complicate an accurate assessment of the patient's baseline level of pruritus—ie, the amount of pruritus associated with the allergy alone. Furthermore, a client might find it overwhelming to administer multiple medications and topical products while also instituting a very restricted diet. In these cases, it might be appropriate to treat the patient's secondary infections before beginning the elimination diet.
The pruritus and discomfort associated with food allergies can be severe, leading to extensive self-trauma. This trauma can itself contribute to an inflammatory response and help to perpetuate pruritus. For this reason, food-allergic patients can receive any antipruritic medication necessary to control their signs during a dietary elimination trial.
Pet owners might find it helpful to keep a diary of their pet's responses during the dietary elimination trial. This diary could be as simple as a record of the date and extent of pruritus (or other clinical signs). Unusual events (visitors, trips to dog parks, etc) should also be recorded, because they might help to identify potential breaks in the diet. These diaries are particularly useful to provide relatively objective evidence of improvement in animals that show only partial response to dietary changes.
Dietary Rechallenge to Diagnose Cutaneous Food Allergy
At the end of a dietary elimination trial, the patient should undergo a controlled dietary rechallenge (provocation). The rechallenge has two purposes: to identify problematic food items and to confirm that any improvement is truly associated with the diet and is not coincidental (eg, due to seasonal allergen changes or better flea control) or the result of placebo effects.
In humans, double-blind, placebo-controlled allergen challenges are considered essential to confirm true hypersensitivity versus placebo responses. Although veterinary patients are not expected to respond to placebo treatment, their owners' interpretation of their response can be influenced. Nonetheless, some patients appear to improve during a diet trial but do not relapse upon challenge (19); these patients are not considered to be food allergic.
Dietary rechallenge can be particularly important if the response to an elimination diet is only partial. In this case, relapse of clinical signs upon rechallenge demonstrates the presence of food allergy; however, lack of complete remission suggests that a second problem (environmental allergen–associated atopic dermatitis, flea allergy, etc) is likely also present.
For all of these reasons, food allergy is not considered to be confirmed unless the patient has both improved on the diet and experienced a flare-up on rechallenge.
Usually, the rechallenge is conducted using items that the patient was eating at the start of the elimination trial. The patient's primary diet is generally the initial challenge item. Alternatively, a challenge with other previously fed food sources (kibble, heartworm preventative, etc) may be performed instead.
An increase in itching or other clinical signs is typically evident within days (sometimes hours) after the challenge is started; however, positive challenge responses can take up to 10–14 days to appear (20). Therefore, most clinicians believe that individual food items should not be introduced any more frequently than every 2 weeks, so that there is no confusion regarding the offending item.
A patient that shows relapse of clinical signs upon rechallenge should be placed back on the elimination diet. Once the patient is comfortable again, the challenge can be resumed, using specific ingredients (chicken, beef, etc) or other food-based items (treats, chewable flea preventatives, etc) to pinpoint the allergy source, but individual ingredient challenge is not always practical or necessary.
Before provocative rechallenge at the conclusion of an elimination diet trial, ideally a withdrawal period (generally 2 weeks) of antipruritic agents should be observed so that an accurate assessment of any residual pruritus can be made. However, discontinuation of antipruritic agents might not be possible in patients demonstrating only partial responses to the diet. Longer withdrawal periods might be required in the case of repositol steroid injections or injectable monoclonal antibodies, such as lokivetmab.
Treatment of Cutaneous Food Allergy
Allergen avoidance
Antipruritic therapy
Food-specific allergen immunotherapy (currently under development)
Treatment of confirmed cutaneous food allergies is typically based on allergen avoidance. Some clients might elect to continue the patient on a test diet that their pet did well on (if the diet is balanced for long-term feeding). Alternatively, clients can cautiously experiment with other diets to find foods their pet might tolerate.
Ideally, dietary control alone is sufficient to keep the patient in full or near-full remission. However, food allergy is often accompanied by other hypersensitivity disorders (environmental allergen–induced atopic dermatitis, flea allergy); therefore, perfect control of pruritus and dermatitis might not be possible unless all factors are addressed.
Pruritus is also expected to worsen if the patient develops a secondary bacterial or yeast infection. In these cases, some form of long-term antipruritic therapy might be required for optimal response.
Food-specific immunotherapy is not yet widely available; however, it might become a valuable tool in the management of food allergy in animals. A potential beneficial effect of food-specific sublingual immunotherapy for desensitization in dogs with food allergy has been demonstrated (21). Although this modality is commonly used in humans, investigation into its use is still in its infancy in veterinary medicine. Nonetheless, this approach offers promise for the adjunctive management of food allergies in animals.
Diet-Associated Dilated Cardiomyopathy
Long-term feeding of some diets has been loosely associated with the development of dietary-associated dilated cardiomyopathy.
In 2018, the FDA began an investigation into the possible association between the development of canine nonhereditary dilated cardiomyopathy (NH-DCM) and feeding of grain-free diets in dogs (22). Subsequent investigation suggested that many of the "suspect diets" contained particularly high proportions of legumes, including pulses (peas, chickpeas, lentils, and dried beans). Other suspect ingredients were potatoes and sweet potatoes (but not soybeans).
Since that time, it has become clear that the situation is likely not that simple. Not all diets meeting this description have been necessarily associated with the development of NH-DCM, and patients can develop NH-DCM while eating diets that do not meet this description.
Other factors that might be associated with the development of NH-DCM include prior or concurrent myocarditis, hyperthyroidism, and other types of nutritional imbalances (low levels of taurine, diets with high levels of insoluble fiber, etc) (23).
The predisposition of large-breed dogs to NH-DCM suggests some genetic influence; however, NH-DCM has been reported in a wide range of dog breeds (including toy breeds) and in cats. One analysis suggested that sampling bias was possible (preferred reporting of dogs with NH-DCM cases that had been eating grain-free/high-lentil diets) and that all cases of DCM need to be evaluated to make any clear statements about causality (23).
Significant improvement of echocardiographic parameters and clinical outcomes in dogs switched from grain-free diets to "traditional" grain-containing diets along with other management of their cardiac disease has been demonstrated (24).
In some reported cases of NH-DCM, longer duration of a grain-free diet appeared to be associated with a worse prognosis. Although suggestive, these findings alone are not clear enough to prove a cause-and-effect relationship between diet and NH-DCM. Nonetheless, some sources have suggested it might be prudent to avoid diets that list pulses among their top 10 ingredients, as well as diets that contain multiple pulses (25).
Key Points
The most common cutaneous clinical sign of food allergy in both dogs and cats is pruritus.
In dogs, the most common food allergens are beef, dairy products, chicken, wheat, and lamb. In cats, the most common food allergens are beef, fish, and chicken.
A strict dietary elimination trial and subsequent provocative rechallenge is the only reliable method for diagnosing food allergies.
For More Information
Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (5): discrepancies between ingredients and labeling in commercial pet foods. BMC Vet Res. 2018;14(1):24.
Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (8): storage mites in commercial pet foods. BMC Vet Res. 2019;15:385.
FDA Investigation Into Potential Link Between Certain Diets and Canine Dilated Cardiomyopathy. FDA.
Also see pet owner content regarding food allergies in dogs, cats, and horses.
References
Miyazawa K, Ito M, Ohsaki K. An equine case of urticaria associated with dry garlic feeding. J Vet Med Sci. 1991;53(4):747-748. doi:10.1292/jvms.53.747
Jubb TF, Graydon RJ. Telogen defluxion associated with hypersensitivity causing alopecia in a horse. Aust Vet J. 2007;85(1-2):56-58. doi:10.1111/j.1751-0813.2006.00086.x
Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (3): prevalence of cutaneous adverse food reactions in dogs and cats. BMC Vet Res. 2016;13:51. doi:10.1186/s12917-017-0973-z
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. 2016:12:9. doi:10.1186/s12917-016-0633-8
Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (7): signalment and cutaneous manifestations of dogs and cats with adverse food reactions. BMC Vet Res. 2019;15:140. doi:10.1186/s12917-019-1880-2
Santoro D, Pucheu-Haston CM, Prost C, Mueller RS, Jackson H. Clinical signs and diagnosis of feline atopic syndrome: detailed guidelines for a correct diagnosis. Vet Dermatol. 2021;32(1):26-e6. doi:10.1111/vde.12935
Mueller RS, Olivry T. Critically appraised topic on adverse food reactions of companion animals (6): prevalence of noncutaneous manifestations of adverse food reactions in dogs and cats. BMC Vet Res. 2018;14:341. doi:10.1186/s12917-018-1656-0
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 in vivo or in vitro tests?BMC Vet Res. 2017;13:275. doi:10.1186/s12917-017-1142-0
Maina E, Matricoti I, Noli C. An assessment of a Western blot method for the investigation of canine cutaneous adverse food reactions. Vet Dermatol. 2018;29(3):217-e78. doi:10.1111/vde.12536
Possebom J, Cruz A, Gmyterco VC, de Farias MR. Combined prick and patch tests for diagnosis of food hypersensitivity in dogs with chronic pruritus. Vet Dermatol. 2022;33(2):124-e36. doi:10.1111/vde.13055
Udraite Vovk LU, Watson A, Dodds WJ, Klinger CJ, Classen J, Mueller RS. Testing for food-specific antibodies in saliva and blood of food allergic and healthy dogs. Vet J. 2019;245:1-6. doi:10.1016/j.tvjl.2018.12.014
Favrot C, Linek M, Fontaine J, et al. Western blot analysis of sera from dogs with suspected food allergy. Vet Dermatol. 2017;28(2):189-e42. doi:10.1111/vde.12412
Johansen C, Mariani C, Mueller RS. Evaluation of canine adverse food reactions by patch testing with single proteins, single carbohydrates and commercial foods. Vet Dermatol. 2017;28(5):473-e109. doi:10.1111/vde.12455
Bexley J, Kingswell N, Olivry T. Serum IgE cross-reactivity between fish and chicken meats in dogs. Vet Dermatol. 2019;30(1):25-e8. doi:10.1111/vde.12691
Olivry T, O'Malley A, Chruszcz M. Evaluation of the theoretical risk of cross-reactivity among recently identified food allergens for dogs. Vet Dermatol. 2022;33(6):523-526. doi:10.1111/vde.13110
Olivry T, Mueller RS, Prélaud P. Critically appraised topic on adverse food reactions of companion animals (1): duration of elimination diets. BMC Vet Res. 2015;11:225. doi:10.1186/s12917-015-0541-3
Fischer N, Spielhofer L, Martini F, Rostaher A, Favrot C. Sensitivity and specificity of a shortened elimination diet protocol for the diagnosis of food-induced atopic dermatitis (FIAD). Vet Dermatol. 2021;(32)3:247-e65. doi:10.1111/vde.12940
Favrot C, Bizikova P, Fischer N, Rostaher A, Olivry T. The usefulness of short-course prednisolone during the initial phase of an elimination diet trial in dogs with food-induced atopic dermatitis. Vet Dermatol. 2019;30(6):498-e149. doi:10.1111/vde.12793
Sofou EI, Aleksandrova S, Chatzis M, Samuel Badulescu E, Saridomichelakis MN. Establishment of clinical criteria for the diagnosis of adverse food reactions in dogs with atopic dermatitis. Vet Dermatol. 2024;35(4):418-431. doi:10.1111/vde.13247
Olivry T, Mueller RS. Critically appraised topic on adverse food reactions of companion animals (9): time to flare of cutaneous signs after a dietary challenge in dogs and cats with food allergies. BMC Vet Res. 2020;16:158. doi:10.1186/s12917-020-02379-3
Maina E, Cox E. A double blind, randomized, placebo controlled trial of the efficacy, quality of life and safety of food allergen-specific sublingual immunotherapy in client owned dogs with adverse food reactions: a small pilot study. Vet Dermatol. 2016;27(5):361-e91. doi:10.1111/vde.12358
US Food and Drug Administration. FDA investigation into potential link between certain diets and canine dilated cardiomyopathy. Updated June 27, 2019. Accessed July 8, 2025.
McCauley SR, Clark SD, Quest BW, Streeter RM, Oxford, EM. Review of canine dilated cardiomyopathy in the wake of diet-associated concerns. J Anim Sci. 2020;98(6):skaa155. doi:10.1093/jas/skaa155
Walker AL, DeFrancesco TC, Bonagura JD, et al. Association of diet with clinical outcomes in dogs with dilated cardiomyopathy and congestive heart failure. J Vet Cardiol. 2022;40:99-109. doi:10.1016/j.jvc.2021.02.001
Smith CE, Parnell LD, Lai CQ, Rush JE, Freeman LM. Investigation of diets associated with dilated cardiomyopathy in dogs using foodomics analysis. Sci Rep. 2021;11(1):15881. doi:10.1038/s41598-021-94464-2
