Hypoallergenic Diets in Dogs and Cats: 2026 Update

Food allergy affects up to 33% of atopic dogs and 22% of pruritic cats. The elimination diet remains, in 2026, the only validated diagnostic tool for confirming food allergy, as no serological or salivary test can confirm it. Discover in this comprehensive article the immunopathological mechanisms and current diagnostic strategies, from the choice of hypoallergenic food to long-term management. Grain-free or insect-based diets, particularities of these diets in cats, the role of the provocation test, and much more.

PART I — NOSOLOGICAL FRAMEWORK AND EPIDEMIOLOGY

Chapter 1 — Definitions and Classification of Adverse Food Reactions

1.1 — Adverse Food Reaction (AFR): General Nosological Framework

The term adverse food reaction (AFR) constitutes a nosological framework encompassing all abnormal clinical responses following the ingestion of a food or food additive. This definition, adopted by international consensus, encompasses heterogeneous pathophysiological mechanisms distinguished by the nature of the biological response involved (Gaschen 2011). AFRs are subdivided into two broad categories: immunological reactions (true food allergies) and non-immunological reactions (food intolerances, food poisoning, pharmacological reactions to biogenic amines). The exact prevalence of AFRs remains difficult to establish precisely, owing to the variability of diagnostic criteria used across studies and the low owner compliance with provocation challenge protocols. Data compiled by Olivry and Mueller (2017) indicate that 1 to 2% of dogs presenting in general practice are affected, a figure that rises to 9 to 40% among pruritic dogs (median: 18%) and 9 to 50% (median: 29%) in dogs displaying a clinical phenotype of atopic dermatitis. In cats, the prevalence among animals presenting with cutaneous signs ranges from 0.22 to 6% depending on the populations studied (Olivry 2017).

1.2 — True Food Allergy vs Food Intolerance

True food allergy is defined by a specific immunological response directed against one or more dietary proteins, involving the adaptive immune system. This response may be mediated by immunoglobulin E (IgE) via a type I hypersensitivity according to the Gell and Coombs classification (Pucheu-Haston 2020), or by T lymphocytes via a type IV hypersensitivity (Jackson 2023). Food intolerance, by contrast, does not involve the adaptive immune system. It results from non-immunological mechanisms such as enzymatic deficiencies (lactase deficiency), pharmacological reactions to biogenic amines (histamine, tyramine contained in certain fermented products), or direct toxic effects (Mueller 2018). The distinction between these two entities is of major clinical importance: true allergy generates reactions reproducible at sometimes minute doses of the allergen, whilst intolerance is often dose-dependent. In clinical veterinary practice, however, this distinction remains difficult to establish without a standardised provocation challenge, as the cutaneous and digestive manifestations are often superimposable.

1.3 — Cutaneous Adverse Food Reaction (CAFR): Definition and International Terminology

The term CAFR designates specifically the dermatological manifestations secondary to the ingestion of a food (Olivry 2019). This terminology has been updated to harmonise nomenclature across different publications. CAFR is distinguished from environmental atopic dermatitis (EAD) by its alimentary aetiology, although both entities share a comparable clinical phenotype — notably non-seasonal pruritus affecting the extremities, ear pinnae, and flexural areas. In dogs, 94% of CAFR cases manifest with pruritus as the dominant sign (Olivry 2019). In cats, the term Feline Atopic Syndrome (FAS) also encompasses feline EAD, reflecting the difficulty of dissociating them without a dietary exclusion regimen.

Labial lesions are frequently present in cases of food allergy

1.4 — IgE-Mediated and Non-IgE-Mediated Mechanisms

The immunopathological mechanisms underpinning canine and feline food allergies involve two main pathways. The IgE-mediated pathway (type I) relies on the production of specific IgE directed against dietary glycoproteins with a molecular weight between 10 and 70 kDa (Cave 2006). Upon re-exposure, these IgE fixed to FcεRI receptors on tissue mast cells provoke mast cell degranulation and the release of histamine, leukotrienes, and prostaglandins, giving rise to erythema, pruritus, and localised oedema. The T-cell pathway (type IV), non-IgE-mediated, involves helper T lymphocytes (Th1 and Th2) and manifests in a delayed manner, between 24 and 72 hours after ingestion. In vitro data (Masuda 2020) indicate that enzymatic hydrolysis, even when generating peptides of very low molecular weight (1 to 3.5 kDa), does not completely suppress the epitopes recognised by T lymphocytes. T lymphocyte activation was detected in approximately 28.8% of dogs tested. However, this cellular recognition remains overwhelmingly below the threshold of clinical reactivity (only approximately 2% of patients reach the lymphocyte activation threshold of 1.2% correlated with symptoms). Consequently, high-quality hydrolysed diets retain remarkable clinical efficacy in vivo and represent an option of choice for the exclusion diet, although very rare residual T lymphocyte-mediated reactivity (type IV) may explain certain refractory failures. This observation underlines that protein hydrolysis, even when extensive, does not completely suppress the T-cell immunogenic potential of dietary proteins.

Chapter 2 — Epidemiology and Prevalence of CAFRs

2.1 — Prevalence in the General Population and Among Pruritic Dogs

The epidemiological data compiled in the series of Critically Appraised Topics published by Olivry and Mueller between 2015 and 2020 provide the current reference framework. The prevalence of CAFRs in the general canine population lies between 1 and 2% (Olivry 2017). This figure increases significantly when considering selected populations: among dogs presenting with chronic pruritus, the median prevalence reaches 18% (range: 9 to 40%), and among those with allergic dermatitis, it rises to 29% (range: 9 to 50%). In cats, data are less abundant but converge towards a prevalence of 12 to 22% among subjects presenting with allergic cutaneous signs and 0.22 to 6% in the general population. These figures justify the systematic integration of the exclusion diet in the investigation of any non-seasonal pruritus in the companion animal.

2.2 — Bimodal Distribution of Age of Onset

The age of onset of CAFRs displays a bimodal distribution. The first age group corresponds to young dogs under one year of age: 38% of cases declare before the age of 12 months and 22% before the age of 6 months (Olivry 2019). The mean age of onset is 2.9 years (range: 1 to 13 years), with a second peak in dogs over 7 years of age. In puppies, this particularity necessitates consideration of food allergy from the first manifestations of pruritus, even before contemplating environmental sensitisation, which typically develops progressively. In cats, the age of onset is more variable, with cases reported from 3 months to 11 years. The bimodal distribution in dogs suggests two distinct sensitisation windows: one early, linked to the immaturity of the intestinal barrier and the gut-associated lymphoid tissue (GALT), and one late, possibly linked to an acquired breakdown of oral tolerance.

2.3 — Breed Predispositions

Several breeds are over-represented in studies on CAFRs. In dogs, the West Highland White Terrier (WHWT) is distinguished by a clinical phenotype marked by generalised pruritus, severe facial erythema, and recurrent pyodermas localised to the ventral trunk and limbs. The Labrador Retriever and Golden Retriever develop chronic bilateral pododermatitis, recurrent ceruminous otitis, and interdigital erythema that progressively extends to the flexural areas. Their response to elimination diets is generally satisfactory, with notable clinical improvement between 4 and 6 weeks. The Boxer presents a cutaneous profile dominated by periocular and perioral erythema, with a frequent digestive component (flatulence, soft stools). The German Shepherd is characterised by severe perineal and ventral involvement, often complicated by deep pyodermas. The Cocker Spaniel develops chronic proliferative external otitis, with secondary Malassezia dermatitis resistant to topical treatments. In cats, the Siamese breed shows a predisposition with a clinical expression predominantly facial and cervical (Olivry 2019). Unlike Labrador ichthyosis (PNPLA1 mutation), no specific susceptibility gene for CAFRs has been identified to date, which constitutes a major gap in the understanding of the genetic determinism of this condition.

 

2.4 — Co-sensitisation and Poly-allergenicity

Food and environmental co-sensitisation represents a frequent clinical reality. A significant proportion of dogs with environmental atopic dermatitis (EAD) simultaneously present a CAFR: estimates vary from 13 to 33% depending on the studies (Jackson 2023). This pathological concurrence complicates the diagnostic approach, as partial improvement under an elimination diet may be masked by the persistence of pruritus linked to the environmental component. Concomitant gastrointestinal disorders (diarrhoea, vomiting, increased defaecation frequency) are reported in 20 to 30% of dogs and cats with CAFR (Mueller 2018). In dogs, animals with an AFR present essentially diarrhoea, 2% isolated vomiting, and 5% both signs combined. In cats, the proportion of vomiting (38%) is higher than in dogs, reflecting more frequent involvement of the upper digestive tract and stomach (Mueller 2018).

2.5 — Epidemiological Data: Emerging Trends and New Studies

Recent data confirm an apparent upward trend in the prevalence of CAFRs, likely multifactorial. The multicentre prospective study by Lewis et al., involving 57 pruritic dogs, reports a CAFR diagnosis rate of 44.7% (21/47 dogs who completed the study), a figure higher than historical data (This rate, higher than historical data, must be interpreted within the context of a highly selected population of patients referred for suspected allergic dermatitis, which introduces a major selection bias (Lewis TP 2025). It cannot be directly extrapolated to the general canine population). This increase could reflect an improvement in diagnostic protocols, greater practitioner awareness, or a genuine modification of allergenic exposure linked to the evolution of commercial dietary formulations. The diversification of protein sources in companion animal foods (increasing use of exotic animal proteins, insects, legumes) modifies the antigenic exposure profile and could explain the emergence of new sensitisations (Villaverde 2024).

PART II — IMMUNOPATHOLOGY AND ALLERGENS

Chapter 3 — Immunopathological Bases of Food Reactions

3.1 — Oral Tolerance and GALT

Oral tolerance relies on CD103+ dendritic cells of the intestinal lamina propria, which capture luminal antigens (through epithelial junctions, and via macrophages presenting trans-epithelial extensions) and migrate to the mesenteric lymph nodes (Jackson 2023). In these lymph nodes, they induce the differentiation of naïve T lymphocytes into regulatory T lymphocytes (Tregs) expressing the transcription factor FoxP3. These Tregs secrete immunosuppressive cytokines — principally IL-10 and TGF-β — which maintain a state of non-reactivity towards dietary antigens. The stability of this mechanism depends on the integrity of the intestinal epithelial barrier, the composition of the intestinal microbiome, and the maturation of the digestive system. In puppies, the immaturity of the GALT (Gut-Associated Lymphoid Tissue) and the increased intestinal permeability create a window of vulnerability that explains the frequency of early sensitisations.

3.2 — Breakdown of Tolerance

Among the proposed mechanisms for the breakdown of oral tolerance is the release of TSLP by damaged enterocytes, well documented in human medicine and in mice. Direct data in dogs and cats are still limited in the literature, and this pathway is currently extrapolated from human models of food allergy.

3.3 — IgE Isotype Class Switching

Isotype class switching towards IgE represents the critical step in allergic sensitisation. Under the influence of IL-4 and IL-13 produced by Th2 lymphocytes, B lymphocytes perform genetic recombination at the level of the Sε switch region of the immunoglobulin heavy chain gene, leading to the production of allergen-specific IgE. These IgE then bind to high-affinity FcεRI receptors expressed on the surface of cutaneous and intestinal tissue mast cells. This overexpression lowers the mast cell degranulation threshold and explains clinical hypersensitivity to low doses of allergens. Upon re-exposure, the simultaneous cross-linking of two adjacent membrane-bound IgE molecules by a multivalent allergen triggers the degranulation cascade, with release of histamine, tryptase, and prostaglandins, responsible for the characteristic pruritus, erythema, and oedema.

3.4 — Non-IgE-Mediated T-Cell Mechanism

The T-cell component of CAFRs constitutes a rapidly expanding area of research. Lymphocyte blastogenesis studies conducted by Fujimura et al. demonstrated significant T lymphocyte proliferation in response to food allergens in dogs with confirmed CAFR (Fujimura 2011). Masuda et al. refined these results using flow cytometry to analyse peripheral blood mononuclear cells (PBMCs) from 316 dogs suspected of food allergy (Masuda 2020). The results show that extracts from hydrolysed diets contained proteins or peptides with a molecular weight between 1 and 3.5 kDa, capable of stimulating CD25low helper T lymphocytes. The rate of positive lymphocyte response to hydrolysed extracts reached 28.8% (91/316 samples) for the first diet tested and 23.7% (75/316) for the second. Among the 186 samples also reactive to avian antigens, these rates rose to 38.7% and 29.6% respectively. However, it is erroneous to conclude that hydrolysed diets present a failure rate of nearly 30% linked to T-cell stimulation. Indeed, this activation only reaches the threshold of clinical relevance (capable of triggering a dermatological relapse in vivo) in approximately 2% of cases. The risk of clinical failure due to T lymphocyte stimulation is therefore very low and confined principally to animals already presenting severe cellular hypersensitivity to the source protein of the hydrolysate (e.g. feather hydrolysate in a dog highly allergic to chicken). Extensively hydrolysed diets consequently remain a highly reliable first-line diagnostic tool.

3.5 — Cross-Reactivities

Cross-reactivities between food allergens represent a major clinical challenge for the selection of novel protein elimination diets. Bexley et al. demonstrated by ELISA significant IgE cross-reactivity between chicken and fish proteins in dogs (Bexley 2019): among canine sera presenting elevated anti-chicken IgE, 97% also reacted with turkey and duck extracts (Olivry 2017). The study by Olivry et al. on 40 canine and 40 feline sera showed that anti-chicken IgE recognised turkey meat (97% of dogs, 84% of cats) and duck meat (97% of dogs, 97% of cats), confirming extensive cross-reactivity within the Galliformes family (Olivry 2017). Beef-lamb cross-reactivity, linked to conserved epitopes among Ruminantia proteins (notably bovine serum albumin Bos d 6 and its ovine homologues), is documented less systematically but must be anticipated when selecting an alternative protein source. However, its actual clinical incidence in canine and feline CAFRs remains insufficiently documented in the veterinary literature to precisely quantify the risk. The pollen-food syndrome, well described in human medicine, is suspected in atopic dogs sensitised to certain grass pollens cross-reacting with cereal proteins (wheat, maize).

Chapter 4 — Principal Food Allergens According to Studies

4.1 — Mueller et al. 2016 Systematic Review (1985–2015): Methodology and Results

The systematic review published by Mueller, Olivry, and Prelaud (2016) constitutes the methodological reference for the identification of food allergens in veterinary medicine. This analysis compiled data from 297 dogs and 78 cats whose CAFR diagnosis had been confirmed by elimination diet followed by individual provocation challenges between 1985 and 2015. The methodology rested on strict inclusion criteria: only studies reporting clinical improvement under an exclusion diet followed by documented recurrence upon re-introduction of the implicated food were retained. Provocations had to be performed with individual ingredients to allow specific identification of the responsible allergen. This methodological rigour explains the relatively limited number of subjects included despite the analysis period spanning 30 years.

4.2 — Principal Allergens in Dogs: Beef (34%), Dairy Products (17%), Chicken (15%), Wheat (13%), Lamb (5%)

In dogs, the hierarchy of food allergens established by Mueller, Olivry, and Prelaud places beef in first position with 34% of positive reactions during provocation challenges, followed by dairy products (17%), chicken (15%), wheat (13%), and lamb (5%). Soya, maize, and egg each represent less than 5% of confirmed sensitisations. These data contradict the popular perception that cereals constitute the principal canine food allergens: in reality, animal proteins (beef, dairy products, chicken, lamb) account for more than 70% of sensitisations. The high frequency of beef as an allergen reflects its near-ubiquitous presence in commercial kibble and food for dogs, confirming the correlation between prolonged dietary exposure and the risk of sensitisation. Wheat, although less frequently implicated than animal proteins, represents the most allergenic carbohydrate source, with reactivity linked to the gliadins and glutenins contained in gluten.

4.3 — Principal Allergens in Cats: Beef (18%), Fish (17%), Chicken (5%)

In cats, the allergenic profile differs appreciably from that of the dog. Beef represents 18% of confirmed sensitisations, followed by fish (17%) and chicken (5%) (Mueller 2018). The position of fish in second place reflects the high proportion of fish proteins in commercial feline food, particularly in wet foods and recipes based on tuna, salmon, and white fish. Dairy products and wheat are reported in fewer than 5% of feline cases. Lamb and egg feature among the minor allergens. Data specific to cats remain limited, however, by the reduced number of subjects having benefited from individual provocation challenges in published studies (78 cats in the Mueller 2016 meta-analysis), and must be interpreted with caution. The emergence of new diets based on insects (Hermetia illucens, Tenebrio molitor) for the feline species could modify this profile in coming years, although allergenic data on these protein sources are still limited.

4.4 — Molecular Characterisation of Epitopes

The molecular characterisation of food allergens by Component-Resolved Diagnostics (CRD) opens new perspectives for understanding sensitisation mechanisms. Bovine serum albumin Bos d 6 (molecular weight: 67 kDa) constitutes one of the principal beef allergens identified in dogs. Its tertiary structure, conserved among mammals, explains the cross-reactivities observed between beef, lamb, and venison. Ovomucoid Gal d 1 (28 kDa), the principal allergen of hen’s egg, presents thermal and enzymatic resistance that maintains its allergenicity after cooking and gastric digestion. Parvalbumin (Gad m 1, ~11.5 kDa) represents a major allergen of fish, with conserved homologues in salmon, trout, and cod (Bexley 2019). Enolase (Gad m 2, ~47-50 kDa) is an additional allergen with a lower prevalence of sensitisation. These molecular data allow anticipation of cross-reactivities when choosing a novel protein for the elimination diet and could, in time, improve the precision of in vitro diagnostic tests.

4.5 — Food Additives and Biogenic Amines

The role of food additives (colorants, preservatives, flavourings) and biogenic amines (histamine, tyramine, putrescine) in AFRs of dogs and cats remains marginal in the scientific literature. Available studies report only rare cases of reactions attributed to specific additives, and no robust evidence supports their frequent involvement in CAFRs (Mueller 2018). Biogenic amines, present in variable concentrations in fermented or poorly preserved foods, can provoke dose-dependent reactions (vasodilation, pruritus) via a direct pharmacological mechanism involving H1 and H2 histamine receptors, without involvement of the adaptive immune system. These reactions constitute food intolerance and not true allergy. The distinction is important in clinical practice, as these reactions do not recur during provocation challenges performed with fresh ingredients of good quality.

4.6 — Comparative Table: Dog vs Cat Allergens

The allergenic profile of dogs and cats presents similarities (predominance of animal proteins, low involvement of cereals) but also notable differences. Beef dominates in both species, with 34% in dogs versus 18% in cats. Fish occupies second place in cats (17%) whilst remaining a minor allergen in dogs (<5%). Chicken represents 15% of canine sensitisations versus 5% of feline sensitisations. Dairy products, frequent in dogs (17%), are rarely reported in cats. Wheat constitutes the third canine allergen (13%) but remains anecdotal in cats. These differences reflect the dietary exposure profiles specific to each species and the typical composition of commercial kibble and wet foods available in the United Kingdom.

4.7 — New Implicated Protein Sources

The rapid evolution of the petfood market is modifying the antigenic exposure profile of dogs and cats. The democratisation of diets based on duck, venison, kangaroo, and salmon in mainstream (OTC) ranges is progressively reducing the repertoire of “novel” proteins for a given animal. Grain-free kibble based on legumes (peas, lentils) and potato, very popular since 2018, introduces new potential allergens whose incidence in CAFRs has not yet been systematically documented.

The question of the cardiovascular safety of these grain-free diets has moreover arisen since the alert published by the FDA in 2018, which recorded 1,100 reports — including 560 cases of dilated cardiomyopathy (DCM) — in dogs of breeds not normally predisposed (Golden Retriever, Labrador Retriever, Bulldog), in association with prolonged consumption of grain-free diets rich in legumes (Freeman 2018). The proposed mechanisms include a taurine deficiency linked to reduced bioavailability of lysine and methionine in formulations with high legume content, an interaction between plant lectins and the intestinal mucosa, and the presence of antinutritional compounds reducing the absorption of sulphur amino acids (Adin 2019). Although the FDA’s 2022 update clarified that causality had not been formally established, this vigilance is warranted when prescribing prolonged grain-free legume-based diets, particularly in at-risk breeds such as the Golden and Labrador Retriever.

The increasing use of insect proteins (black soldier fly meal, Hermetia illucens; mealworm, Tenebrio molitor) in animal food formulations constitutes an emerging trend. The study by Majewski et al. (2021), published in Animals (Basel), demonstrated in atopic dogs the binding of canine serum IgE to proteins extracted from Tenebrio molitor, with identification of 17 allergenic proteins including tropomyosin, α-amylase, and cuticular protein Tm-E1a — all three recognised as cross-reactive allergens with storage and house dust mites (Dermatophagoides farinae, Tyrophagus putrescentiae). Rodríguez-Pérez et al. completed these data with an in silico mapping of B and T epitopes of tropomyosin, confirming the phylogenetic conservation of this molecule across all arthropods and the bidirectional nature of cross-reactivity: an animal sensitised to mites may react to insects, and vice versa (Rodríguez-Pérez 2024). These data call for caution in the use of insect-based diets in any dog or cat with documented sensitisation to mites. In the absence of controlled provocation studies in canine and feline species, these diets should not be used as elimination diets in atopic animals sensitised to mites, pending clinical validation of this risk.

PART III — CLINICAL EXPRESSION

Chapter 5 — Clinical Manifestations in Dogs

5.1 — Non-Seasonal Pruritus

Non-seasonal pruritus constitutes the cardinal sign of CAFRs in dogs, reported in 94% of subjects in the systematic review by Olivry and Mueller (2019). This pruritus is characterised by its persistence throughout the year, independent of pollen seasons, in contrast to the pruritus of strictly environmental EAD, which presents marked seasonality in temperate regions. The intensity of pruritus, assessed by the Pruritus Visual Analogue Scale (PVAS, 0-10), typically lies between 5 and 9 in dogs with untreated CAFR. The diagnostic value of the non-seasonal character of pruritus is, however, relative: approximately 30% of atopic dogs sensitised to mites also present perennial pruritus. Therefore, the non-seasonal character points towards CAFR but does not confirm it. An incomplete clinical response to glucocorticoids is frequently reported in CAFRs and constitutes an indirect clinical indicator pointing towards a food component. However, no quantitative response threshold (such as 50%) has been validated by a controlled diagnostic study. This criterion must be interpreted in conjunction with other clinical indicators (non-seasonal character, digestive signs, age of onset) and can in no way substitute for the elimination diet.

5.2 — Topographical Distribution

The topographical distribution of cutaneous lesions in canine CAFRs is superimposable upon that of EAD, rendering clinical distinction impossible without an exclusion diet. Recurrent bilateral external otitis constitutes one of the most frequent manifestations of canine CAFRs, reported in 24 to 80% of cases depending on the studies, with a median of approximately 50-60% (Olivry and Mueller, 2019). This sign is, however, also very frequent in environmental EAD and does not present sufficient diagnostic specificity to differentiate between the two aetiologies. Pedal involvement manifests as an erythematous interdigital pododermatitis, with marked pruritus of the palmar and plantar interdigital spaces. The axillary, inguinal, and perineal regions present diffuse erythema with skin thickening (lichenification) in cases of chronic evolution. The ventral abdomen and the inner aspect of the thighs, from the inguinal region down to the inner aspect of the hocks, are frequently affected. The coat may present a brownish colouration due to chronic licking, visible in dogs with a pale coat. The skin of the flexural areas (elbows, carpi, tarsi) shows hyperpigmentation and lichenification attesting to the chronicity of the pruritus.

5.3 — Primary and Secondary Lesions

Primary lesions of canine CAFRs include erythema (diffuse or localised), papules, and, more rarely, urticaria. Erythema represents the earliest lesion, observable within the first hours after allergen exposure during provocation challenges. Papules, of small size (2-5 mm), are dispersed over the ventral trunk and limbs. Secondary lesions result from self-trauma and opportunistic superinfections. Superficial pyoderma caused by Staphylococcus pseudintermedius constitutes a frequent complication of allergic dermatitis, including CAFRs, although the exact rate of occurrence specifically in CAFRs is not quantified separately in the literature. The high prevalence of these secondary superinfections requires their detection and treatment before and during the elimination diet. Malassezia dermatitis (proliferation of Malassezia pachydermatis) aggravates pruritus and generates a greasy, malodorous erythema, predominating in the skin folds, ear canals, and interdigital spaces. These secondary superinfections must be treated before and during the elimination diet, as their persistence may mask the clinical improvement attributable to dietary allergen exclusion and simulate a diagnostic failure.

5.4 — Relative Resistance to Glucocorticoids

Relative resistance to glucocorticoids constitutes an indirect diagnostic indicator in favour of a food component. Dogs with CAFR show a significantly lower pruritus response to prednisolone than that observed in strictly environmental EAD. Favrot et al. assessed the usefulness of a short course of corticotherapy (prednisolone, 0.5 mg/kg/day for 14 days) during the initial phase of the elimination diet in dogs with food-induced atopic dermatitis (Favrot 2019). The results show that the addition of a short course of corticotherapy improves owner compliance by reducing pruritus during the first weeks, without compromising interpretation of the elimination diet at its conclusion. Oclacitinib at a dose of 0.4-0.6 mg/kg orally twice daily for 14 days then once daily constitutes an alternative for pruritus control during the initial phase of the diet.

5.5 — Concomitant Gastrointestinal Manifestations

Gastrointestinal manifestations associated with canine CAFRs are reported in 20 to 30% of subjects (Mueller 2018). Among these dogs, diarrhoea is the predominant manifestation, often associated with vomiting, but isolated vomiting is rarely observed (Mueller and Olivry, 2018). The most frequent signs include increased defaecation frequency (>3 stools per day), chronic small intestinal or colonic diarrhoea, borborygmi, flatulence, and, more rarely, vomiting. The use of second-generation diets based on ultra-hydrolysed proteins shows remarkable efficacy in refractory chronic canine enteropathy cases, but requires prolonged compliance. A pilot study (Freiche 2025) demonstrated that the clinical remission rate, initially 61.5% after 5 weeks, progresses significantly to exceed 90% after 10 weeks of strict dietary management. This slow kinetics highlights the importance of maintaining gastrointestinal dietary trials for a minimum duration of 8 to 10 weeks before concluding therapeutic failure. Rodrigues et al. confirmed in a multicentre retrospective study the association between the type of diet used and the therapeutic response in dogs with chronic enteropathy, underscoring the importance of food choice in overall management. Assessment of the digestive system by coprological examination, and if necessary by endoscopy with intestinal biopsies, remains recommended in cases of predominant or resistant digestive signs (Rodrigues 2025).

Chapter 6 — Clinical Manifestations in Cats

6.1 — Feline Atopic Syndrome (FAS): Definition and Place of CAFRs

The Feline Atopic Syndrome (FAS) encompasses all allergic dermatitis in cats, whether of dietary origin (CAFR) or environmental (feline EAD). This classification, proposed by Hobi et al. (Hobi 2011) and taken up in the international consensus, reflects the clinical impossibility of distinguishing these two aetiologies without a dietary exclusion regimen. CAFRs represent a significant proportion of FAS: 12 to 22% of pruritic cats present clinical improvement under an elimination diet confirmed by provocation challenge (Olivry 2017). FAS is characterised by a clinical polymorphism specific to the feline species, with four principal cutaneous patterns that may coexist in the same subject.

6.2 — Clinical Patterns

The clinical expression of FAS of dietary origin borrows from the four classical cutaneous patterns of feline allergy. The eosinophilic granuloma complex includes the eosinophilic plaque (erythematous, raised, erosive plaque, localised to the inner aspect of the thighs and ventral abdomen), the indolent ulcer (upper labial ulcer, non-painful, ovoid in shape), and the linear granuloma (firm, linear nodule, localised to the caudal aspect of the thighs). Miliary dermatitis, characterised by multiple papulo-crusts disseminated over the dorsal trunk and neck, represents the most frequent pattern. Self-induced alopecia, long described as “psychogenic”, results in reality from subtle pruritus and compulsive licking; it predominates on the ventral abdomen and inner aspect of the thighs, generating bilateral symmetrical alopecia without visible skin lesions. Silva et al. reported the benefit of a hypoallergenic diet in the control of eosinophilic oral lesions in cats, confirming the link between CAFR and the oral eosinophilic complex (Silva 2024).

6.3 — Facial and Cervical Pruritus

Facial and cervical pruritus constitutes a suggestive, though not pathognomonic, clinical presentation of CAFR in cats. Facial excoriations, localised to the periocular, temporal, and pretragal regions, are often severe and lead to deep erosions with serosanguineous crusts. Dorsal cervical pruritus (dorsal aspect of the neck and base of the ears) generates linear self-traumatic lesions (claw-mark excoriations) that may be confused with ectoparasitosis. The combination of facial pruritus + cervical pruritus + miliary dermatitis should prompt consideration of CAFR as a priority and justifies implementation of an elimination diet after exclusion of ectoparasites. The severity of facial pruritus has a direct impact on the cat’s well-being and quality of life, justifying the use of an accompanying antipruritic treatment during the initial phase of the diet.

6.4 — Extra-Cutaneous Manifestations

Extra-cutaneous manifestations of feline CAFRs include digestive signs (vomiting in 38% of cases, diarrhoea in 45%, both combined in 18%; Mueller 2018), bilateral conjunctivitis, chronic rhinitis, and, more rarely, respiratory signs (sneezing, wheezing). The high proportion of vomiting in cats (38% vs 2% in dogs) reflects more frequent involvement of the upper digestive tract and stomach. Allergic conjunctivitis, characterised by bilateral chemosis and serous discharge, is reported in approximately 10% of FAS cases of dietary origin. Hyperactive behaviour and increased frequency of vocalisation have been described anecdotally in certain studies.

6.5 — Semiological Differences Between Dogs and Cats

The semiological differences between the two species are fundamental for orienting the diagnostic approach. In dogs, pruritus is the dominant sign in 94% of cases, with a characteristic pedal, auricular, and inguinal topography. In cats, the cutaneous expression is more polymorphic, with a predominance of facial and cervical pruritus, and the absence of significant pododermatitis. Recurrent external otitis, frequent in dogs (50-80%), is rare in cats (<10%). Digestive signs, present in 20-30% of dogs, affect 40-50% of cats. Resistance to glucocorticoids, indicative of a food component in dogs, is less well documented in cats. The optimal duration of the elimination diet is comparable in both species (minimum 8 weeks), but the practical constraints differ considerably due to feline food neophobia and the risk of hepatic lipidosis.

PART IV — DIAGNOSTIC APPROACH AND PLACE IN ATOPIC INVESTIGATION

Chapter 7 — Differential Diagnosis

7.1 — Diagnostic Algorithm for Chronic Non-Seasonal Pruritus

The investigation of chronic non-seasonal pruritus in dogs and cats follows a sequential algorithm whose rigour conditions the reliability of the final diagnosis. The first step consists in excluding ectoparasitoses (sarcoptic mange, demodicosis, cheyletiellosis, flea allergy) by systematic empirical antiparasitic treatment for 6 to 8 weeks. The second step addresses the treatment of bacterial and fungal cutaneous superinfections that maintain pruritus independently of the primary aetiology. The third step, once ectoparasitoses and superinfections have been excluded or controlled, corresponds to the investigation of atopic dermatitis, of which CAFR represents an essential component. The elimination diet is part of this third step and should be conducted before or during the environmental allergological assessment (intradermal or serum IgE tests).

7.2 — Position of the Exclusion Diet in the Atopic Approach

The question of the sequence between the elimination diet and environmental allergological tests is the subject of debate within the veterinary dermatological community. Two approaches coexist. The sequential approach advocates performing the elimination diet first, in order to quantify the dietary component of pruritus before any environmental assessment. The parallel approach proposes conducting the exclusion diet and intradermal/serum tests simultaneously, which reduces the overall duration of investigation but complicates interpretation of results. Hensel et al. proposed clinical criteria for directing the indication of the exclusion diet: non-seasonal pruritus, age of onset under 1 year or over 7 years, recurrent otitis, partial resistance to glucocorticoids, and the presence of concomitant digestive signs. The presence of two or more of these criteria increases the pre-test probability of CAFR and justifies prioritised implementation of the elimination diet (Hensel 2015).

7.3 — Hensel Criteria for Indication of the Exclusion Diet

The criteria published by Hensel et al. provide a structured decision-making framework for the indication of the elimination diet in the investigation of chronic pruritus. These criteria take into account the non-seasonal character of pruritus (sensitivity: 82%), the topographical distribution of lesions (perianal involvement, bilateral auricular involvement), resistance to glucocorticoids, the presence of concomitant gastrointestinal disorders, and age of onset (<6 months or >6 years). The combination of these criteria does not replace the elimination diet but improves the selection of cases most likely to benefit from this approach. The clinical criteria proposed by Favrot et al. and the recommendations of Hensel et al. (Hensel 2015) provide a framework for the diagnosis of canine atopic dermatitis, but do not constitute criteria specifically validated for predicting the probability of a CAFR. Several clinical elements — non-seasonal pruritus, early (<1 year) or late (>7 years) age of onset, recurrent otitis, concomitant digestive signs, suboptimal response to glucocorticoids — clinically orient towards a food component and justify implementation of an elimination diet, but their specific predictive value for CAFR has not been formally calculated.

7.4 — Critique of Diagnostic Tests

Alternative tests to the elimination diet (serum food-specific IgE tests, salivary tests, hair tests, food intradermal tests) do not possess the reliability necessary to diagnose CAFRs (Mueller 2017). The study by Coyner and Schick demonstrated that hair and salivary tests cannot differentiate atopic dogs from healthy subjects (Coyner 2019). Lam et al. confirmed the absence of clinical correlation of food IgE and IgG serum tests in dogs without confirmed allergic reactions (Lam 2019). Vovk et al. assessed the accuracy of commercially available food serological tests in 2024 and concluded that their specificity and sensitivity are insufficient to justify their diagnostic use (Vovk 2024). The information provided by these tests may mislead the practitioner and owner, leading to unfounded dietary exclusions or, conversely, a false sense of security.

7.5 — “Why Are Food Blood Tests Unreliable?”

The detection of serum IgE specific to a food allergen indicates only immunological sensitisation, and not clinical reactivity. A dog or cat may present elevated IgE levels directed against beef or chicken without manifesting the slightest cutaneous or digestive reaction upon ingestion of these proteins. This phenomenon, termed clinically silent sensitisation, is frequent and reflects oral tolerance maintained despite the presence of circulating IgE. Conversely, T-cell (type IV) reactions entirely escape detection by serum IgE tests. Food serological tests (IgE and IgG) present a high rate of false positives, with significant overlap of results between healthy dogs and dogs with confirmed CAFR. This rate varies depending on the commercial platform, the type of immunoglobulin measured, and the allergen tested. The totality of available data (Mueller 2017, Lam et al. 2019, Vovk et al. 2024) converges towards the conclusion that these tests do not possess the reliability necessary to confirm or exclude a CAFR diagnosis. The elimination diet followed by provocation challenge remains the only diagnostic tool validated by scientific evidence.

7.6 — The Exclusion Diet (EDT): The Only Validated Gold Standard

The Elimination Diet Trial (EDT), followed by a provocation challenge, constitutes the only validated diagnostic tool for confirming CAFRs in dogs and cats (Olivry 2015, Mueller 2018, Jackson 2023, Villaverde 2024). The principle rests on the exclusive administration, for a minimum duration of 8 weeks, of a food containing no protein to which the animal has previously been exposed, or containing hydrolysed proteins of sufficiently low molecular weight as to not trigger an immune response. Clinical improvement (pruritus reduction ≥50%, decrease in CADESI-04) followed by recurrence of signs upon re-introduction of the previous food confirms the diagnosis. The absence of provocation permits only a presumptive diagnosis, as improvement under the diet may result from non-specific effects (modification of intestinal flora, reduction of biogenic amines, improved digestion).

PART V — ELIMINATION DIETS: PRINCIPLES AND DETAILED IMPLEMENTATION

Chapter 8 — General Principles of Dietary Exclusion

8.1 — Fundamental Principle: Feeding Without Any Possible Sensitising Antigen

The fundamental principle of the dietary exclusion regimen rests on the total avoidance of any antigen that may have induced an immune sensitisation in the animal. This avoidance must be absolute: the slightest exposure, even in minute quantity, may suffice to maintain the immune response and mask the expected clinical improvement. The diet must contain exclusively protein and carbohydrate sources to which the animal has never been exposed (novel protein), or whose allergenic potential has been reduced by enzymatic hydrolysis below the IgE reactivity threshold (<5 kDa according to Cave 2006).

8.2 — Comprehensive Collection of Dietary History

The comprehensive collection of dietary history constitutes the first operational step of the elimination diet. This clinical history must record all commercial foods (all brands and ranges of kibble and wet food consumed since birth), treats (chews, bones, rewards), table scraps, dietary supplements (omega-3, vitamins, fatty acids), flavoured medications (palatable tablets containing animal proteins such as chicken or beef as an excipient), and topicals liable to be licked (toothpastes, balms). Detailed analysis of the composition of each food (ingredient list on the packaging) allows establishment of the list of proteins to which the animal has been exposed and orientates the choice of a “novel” protein source.

8.3 — Owner Education: The Primary Cause of Failure = Non-Compliance

Owner non-compliance represents the first documented cause of failure of elimination diets. Sources of protocol deviation include administration of unauthorised treats, access to the food of other animals in the household, persistence of flavoured medications, and feeding by third parties (children, neighbours, carers). Owner education must be conducted in a structured manner, with provision of a written document detailing the rules of the diet and the exhaustive list of prohibited items. A telephone follow-up at 2 weeks and a monitoring consultation at 4 weeks are recommended to verify compliance and encourage continuation of the protocol.

8.4 — Involvement of the Entire Household

All persons in contact with the animal — family members, children, carers, dog-sitters, neighbours liable to distribute treats — must be informed of the rules of the elimination diet. Dogs living outdoors or with access to a garden must be monitored to prevent ingestion of waste, faeces from other animals, or accessible food. In cases of cohabitation with other animals, feeding bowls must be separated and meals supervised. The cat’s food must be placed out of reach of the dog, and vice versa.

8.5 — The Three Main Categories of Available Diets

Three main categories of elimination diets are available in clinical veterinary practice in 2026. Novel Protein Diets use a protein source to which the animal has never been exposed (rabbit, venison, kangaroo, duck, trout, goat). Hydrolysed protein diets contain proteins whose molecular weight has been reduced by enzymatic hydrolysis, theoretically below the IgE reactivity threshold. Elemental diets based on free amino acids constitute the most hypoallergenic form, devoid of any peptide capable of provoking an immune response. The choice between these options depends on the animal’s dietary history, the foreseeable owner compliance, the cost of the diet, and the palatability for the species concerned.

Chapter 9 — Duration of the Diet, Monitoring, and Response Criteria

9.1 — Evidence-Based Recommendations

The meta-analysis by Olivry, Mueller, and Prélaud (2015) constitutes the reference for determining the optimal duration of the elimination diet. This analysis compiled data from multiple studies in which the kinetics of clinical response to the diet had been documented. The results show that a duration of 5 weeks allows remission to be achieved in 80% of responding dogs and 85% of responding cats. A duration of 8 weeks raises this rate to 90% in both species. The minimum recommended duration is therefore 8 weeks, with extension to 10-12 weeks in complex cases (concomitant EAD, recurrent superinfections, partial response at 8 weeks).

Analysis of the response kinetics shows that 50% of responding dogs present significant improvement by the third week of the diet, and 80% by 5-6 weeks (Olivry 2015). In cats, the kinetics are comparable, with 85% remission at 6 weeks. The study by Lewis et al. (2025) confirms that more than half of subjects diagnosed with CAFR require more than 4 weeks to show a significant reduction in PVAS score, with a baseline PVAS score of 7.4 reduced by 1.8 ± 2.2 points after 8 weeks.

The 8-week duration raises the remission rate to 90% in both species, a threshold beyond which the marginal diagnostic gain becomes small (Olivry 2015). This 90% milestone constitutes the scientific rationale for the international recommendation of 8 weeks as the minimum standard duration of the elimination diet.

9.2 — Recommended Duration: Minimum 8 Weeks and 10 to 12 Weeks in Complex Cases

The remaining 10% of responders require extension to 10-12 weeks, justified in cases presenting concomitant EAD not yet stabilised, persistent superinfections, or a complex allergenic history. Fischer et al. assessed a shortened elimination diet protocol and showed that diagnostic sensitivity decreased significantly below 6 weeks, confirming that any shortening of the protocol exposes to a risk of false negatives (Fischer 2021).

9.3 — Clinical Monitoring

Clinical monitoring during the elimination diet relies on consultations at regular intervals: week 2 (compliance verification and treatment of superinfections), week 4 (first interim assessment), week 8 (final response assessment). Parameters to be assessed include the pruritus score (PVAS), the cutaneous lesion score (CADESI-04 in dogs, SCORFAD in cats), coat and skin condition, stool frequency and consistency, and the animal’s overall well-being.

9.4 — Objective Assessment Tools: PVAS, CADESI, SCORFAD

The SCORFAD (Scoring Feline Allergic Dermatitis) is a validated score specific to cats, assessing excoriative lesions, miliary dermatitis, self-induced alopecia, and eosinophilic complex lesions. CADESI-04 (0-180) and PVAS (0-10) complete the battery of standardised tools in dogs. The combined use of these scores enables objective, reproducible, and comparative monitoring between consultations.

9.5 — Management of Secondary Superinfections During the Diet: Do Not Confuse Them with Failure

Management of secondary superinfections (Staphylococcus pseudintermedius pyoderma, Malassezia pachydermatis dermatitis, otitis) during the diet is imperative: their persistence may simulate diet failure and must not be confused with absence of response to dietary exclusion. A targeted antimicrobial treatment for pyodermas and/or an antifungal agent for Malassezia dermatitis must be instituted in parallel with the diet, based on laboratory findings.

Chapter 10 — The Provocation Challenge: Why Is It Indispensable?

10.1 — Definition and Justification

The oral food challenge (OFC) consists of re-introducing the previous food or a specific ingredient after the elimination period, in order to confirm the CAFR diagnosis through recurrence of clinical signs. Remission under the elimination diet without provocation constitutes only a presumptive diagnosis: clinical improvement may result from non-specific effects of the dietary change (modification of the intestinal microbiome, improved digestibility, reduction of biogenic amines). Provocation is the only means of distinguishing a true CAFR from fortuitous improvement and of confirming the diagnosis.

10.2 — Time to Reappearance of Signs: 7–14 Days According to Studies

The time to reappearance of clinical signs after provocation (Time to Flare, TTF) constitutes a key parameter for the interpretation of provocation challenges. In dogs, 85% of positive provocations manifest within the first 7 days, and 95% within the first 14 days. In cats, the delay is comparable, with 80% of recurrences within 7 days and 90% within 14 days. Shimakura and Kawano reported a median TTF of 3 days (range: 1-14 days) in Japanese dogs subjected to individual food provocations (Shimakura 2021).

10.3 — 2020 Data: Meta-analysis on Post-Provocation Flare Delay (234 Dogs, 83 Cats)

The meta-analysis by Olivry and Mueller (2020), involving provocation challenges in 234 dogs and 83 cats, confirms these delays and provides the most robust database to date. Cutaneous reactions (erythema, pruritus) appear on average more rapidly (median: 2-3 days) than digestive signs (median: 5-7 days). This data justifies a minimum provocation duration of 14 days before concluding a negative result.

10.4 — Owner and Practitioner Reluctance: Communication Strategies

Owner reluctance to perform the provocation challenge constitutes a frequent obstacle in clinical practice. After 8 weeks of a demanding and costly diet, the prospect of a deliberate recurrence of itching in their companion is often poorly accepted. The communication strategy must emphasise that provocation is indispensable for confirming the diagnosis, adapting long-term management, and identifying the specific allergens to avoid. The veterinary dermatologist’s advice helps to overcome this reluctance by explaining that the provocation is of short duration and that the signs are reversible.

10.5 — Individual Provocation Challenges by Ingredient: Sequential Methodology

The individual provocation protocol consists of re-introducing a single ingredient (for example: cooked chicken alone) for 7 to 14 days, whilst maintaining the elimination diet as the base. In cases of sign recurrence, the ingredient is withdrawn and the elimination diet is resumed until remission before testing the next ingredient. This sequential approach allows identification of individual allergens and construction of a personalised maintenance diet.

10.6 — Value of Provocation for Distinguishing CAFR from Concomitant EAD

The provocation challenge with complete return to the previous food allows CAFR to be distinguished from concomitant EAD. If pruritus does not recur despite complete re-introduction, the food component is excluded and the diagnosis must be reassessed in favour of strictly environmental EAD. If pruritus only partially recurs, the coexistence of CAFR and EAD is probable — a scenario estimated in 13 to 33% of atopic dogs (Jackson 2023).

10.7 — Practical Provocation Protocol: Duration Per Ingredient, Management of Positive Results

Each ingredient must be re-introduced for 7 to 14 days. Positivity is defined by the reappearance of pruritus (increase in PVAS ≥2 points) or recurrence of cutaneous lesions (increase in CADESI-04 ≥15 points). In cases of positive provocation, the ingredient is immediately withdrawn and the elimination diet is resumed for 2 to 4 weeks before testing the next ingredient. The order of provocations prioritises the most frequently implicated proteins first (beef, chicken, dairy products).

10.8 — Box: “Why Is the Provocation Test Mandatory to Confirm the Diagnosis?”

The provocation test remains mandatory because remission under the elimination diet alone constitutes only a presumptive diagnosis. Clinical improvement may result from non-specific factors: modification of the intestinal microbiome, reduction of biogenic amine intake, improved digestion, or even seasonal fluctuations of EAD. Only the reproducible recurrence of signs upon re-introduction of the previous food confirms the causal link between allergen ingestion and clinical manifestations.

PART VI — HOME-PREPARED VERSUS INDUSTRIAL DIET

Chapter 11 — Home-Prepared Diet: Value, Protocol, and Risks

11.1 — Advantage No. 1: Absolute Certainty of Composition, Absence of Cross-Contamination

The principal advantage of the home-prepared diet lies in the absolute certainty of its composition: the owner controls every ingredient, eliminating any risk of cross-contamination. Unlike commercial foods, no shared production line can introduce undeclared allergens. This certainty is particularly valuable in poly-allergic animals or those who have failed an industrial hydrolysed diet.

The protocol rests on the principle of the single protein/carbohydrate pair: a single protein source associated with a single carbohydrate source, with no other ingredient added (no salt, no flavoured oil, no spice, no sauce). This principle of maximum simplicity maximises diagnostic reliability by limiting dietary variables to two identifiable components.

Selection of the protein source must be guided by the comprehensive dietary history of the animal. Recommended sources in 2026 include rabbit, venison, kangaroo, duck, trout, tilapia, and goat. The choice of a protein never previously ingested by the animal is the absolute prerequisite of the approach.

Permitted carbohydrate sources include white rice, potato, quinoa, and sweet potato. White rice constitutes the safest carbohydrate source from a nutritional standpoint and the best tolerated by the canine and feline digestive system. Quinoa, whilst potentially usable, contains antinutrients and its digestibility is inferior; it is less recommended as a first choice. Potato remains a valid option for an elimination diet of limited duration (8-12 weeks). Cooking is obligatory: thermal denaturation modifies the three-dimensional structure of proteins and may reduce their IgE reactivity, although certain heat-resistant sequential epitopes maintain their allergenicity. The recommended protein/carbohydrate ratio is 1:2 to 1:3 in fresh weight.

11.2 — Obligatory Cooking: Effect of Thermal Denaturation on IgE-Reactive Epitopes

Cooking at a temperature above 70°C for at least 20 minutes causes denaturation of dietary proteins, altering conformational epitopes recognised by IgE. However, linear (sequential) epitopes resist this denaturation and maintain residual allergenic potential. Beef and chicken thus retain significant allergenicity after cooking, as evidenced by the rates of positive provocation challenges reported in the literature.

Prolonged boiling (>30 minutes at 100°C) reduces allergenicity more than rapid high-temperature cooking (grilling or frying), by fragmenting conformational epitopes without generating neo-antigens.

Conversely, dry cooking at high temperature (>120°C — oven, grill, frying, extrusion) provokes the Maillard reaction, a non-enzymatic glycation of proteins that creates new antigenic structures (advanced glycation end-products, AGEs) liable to increase the immunogenicity of cooked foods (Koppelman 2021). Van Broekhoven et al. confirmed that intensive thermal processes modify the cross-reactive allergenic profile of arthropod proteins, with direct implications for insect-based diets (Van Broekhoven 2016). Consequently, boiling in water constitutes the recommended mode of preparation for home-prepared elimination diets, preferable to any dry cooking method for minimising the residual allergenicity of the proteins used.

11.3 — Absolute Prohibitions: Salt, Flavoured Oils, Spices, Sauces, Additives

The prohibitions of the home-prepared elimination diet are absolute: no salt, no flavoured oil, no spice, sauce, condiment, or additive must be added to the preparation. Any deviation, however minor, may introduce hidden proteins (beef stock, chicken flavouring) liable to falsify the diagnostic result. Neutral vegetable oils (rapeseed, sunflower) are permitted in limited quantities as a source of essential fatty acids.

11.4 — Nutritional Risks

The nutritional risks of the home-prepared diet constitute its principal limitation. A diet composed exclusively of one meat and one starchy food is systematically unbalanced in calcium (Ca/P ratio inverted to 1:10-1:20 instead of 1:1-2:1), essential fatty acids (omega-3 and omega-6), fat-soluble vitamins (A, D, E), and trace elements (zinc, copper, iodine). Stockman et al. assessed recipes for home-prepared diets: 95% failed to meet the minimum nutritional standards of AAFCO or FEDIAF (Stockman 2013).

11.5 — Necessity of Supervision by a Veterinary Nutritionist Beyond 4–6 Weeks

Beyond 4 to 6 weeks, supervision by a veterinary nutritionist is recommended to formulate a balanced maintenance diet if the home-prepared diet must be continued long-term. This specialist consultation enables calculation of macro- and micronutrient intakes, adjustment of quantities, and prevention of long-term deficiencies that could compromise the health and vitality of the animal.

11.6 — Systematic Supplementation

Systematic supplementation with calcium carbonate (100-200 mg/kg of fresh food), fish oil rich in omega-3 (EPA/DHA, 50-100 mg/kg/day), a vitamin complex, and zinc is indispensable from the outset of the diet. The benefits of this supplementation extend beyond simple correction of deficiencies: omega-3 fatty acids exert a documented anti-inflammatory effect on the cutaneous barrier (reduction of PGE2 and LTB4 production) which may contribute to the clinical improvement observed during the diet.

11.7 — Inadequacy for Permanent Use Without Balanced Formulation

A home-prepared diet not formulated by a veterinary nutritionist is unsuitable for permanent use. Cumulative deficiencies in calcium, zinc, and fat-soluble vitamins lead to skeletal problems (osteodystrophy in puppies, pathological fractures in adults), cutaneous problems (alopecia, hyperkeratosis), and immunological problems after several months. Consequently, transition to a balanced industrial therapeutic food or the formulation of a complete home-prepared diet by a specialist constitutes an imperative beyond the diagnostic phase.

Chapter 12 — Industrial Diet: Advantages, Disadvantages, and Cross-Contamination

12.1 — Advantages of Industrial Veterinary Therapeutic Diets: Convenience, Tested Palatability, Nutritional Balance

Industrial veterinary therapeutic diets offer major practical advantages: ease of implementation, tested palatability, complete nutritional balance compliant with AAFCO/FEDIAF standards, and factory quality control. Their formulation guarantees adequate provision of nutrients, fats, vitamins, and trace elements, eliminating the risk of nutritional deficiency inherent in the non-formulated home-prepared diet.

12.2 — Caution Regarding OTC Hypoallergenic Diets

Cross-Contamination: Major Problem with OTC Foods

Cross-contamination of commercial OTC (over-the-counter, non-veterinary) foods constitutes, however, a major problem, documented by multiple independent studies using molecular detection techniques (PCR, ELISA, microarray). This phenomenon results from shared production lines, contamination of raw materials, and the absence of validated cleaning procedures between manufacturing runs.

Systematic Review: 40% of OTC Batches Contaminated

Olivry et al. demonstrated that 40% of OTC food batches contained undeclared allergens not listed on the packaging (Olivry 2018). Ricci et al. (2018) analysed 11 limited-antigen dietary wet foods by PCR microarray: 54.5% (6/11) were contaminated by undeclared animal proteins. Horvath-Ungerboeck et al. had reported similar results for dry foods, with beef and pork as the most frequent contaminants (Horvath-Ungerboeck 2017).

PCR/ELISA Data: 100% of Tested Feline Foods Containing Undeclared DNA

Kępińska-Pacelik et al. (2023) confirmed by quantitative PCR that 65% of OTC canine kibble contained undeclared chicken DNA, and 41% undeclared pork DNA. Preckel et al. (2023) detected by 16S rDNA metagenomic analysis up to 19 undeclared animal species in a single sample. For feline foods, Preckel et al. and Kępińska-Pacelik et al. (2023) showed that 100% of tested samples contained DNA from undeclared species (Preckel 2023). These data raise major traceability issues for the petfood industry and call into question the reliability of limited-antigen kibble and wet foods sold in supermarkets.

2022–2024 Data: 27% of Canine Kibble Containing Undeclared Chicken DNA

The extent of contamination documented between 2022 and 2024 confirms that this phenomenon is not anecdotal. The converging data of Kępińska-Pacelik (2023) and Preckel (2023) demonstrate that OTC “limited antigen” foods cannot be considered reliable for an EDT. The sensitivity of current PCR methods (detection of DNA at concentrations of the order of picograms) reveals contaminations invisible to conventional analyses, making visual or chemical verification insufficient.

Contamination Mechanisms: Shared Lines, Contaminated Raw Materials

The contamination mechanisms are multiple: production lines shared between different formulations (manufacturing chicken kibble on the same line as a “chicken-free” diet leaves protein residues), contamination of upstream raw materials (animal meals, fats, flavourings), and cross-contamination during storage and packaging. The absence of regulation requiring systematic PCR control of OTC batches aggravates this situation.

Regulatory Conclusion: OTC Foods Must Not Be Used for an EDT

OTC foods, including those labelled as “hypoallergenic” or “limited antigen”, must not be used for a diagnostic elimination diet. Only veterinary therapeutic foods manufactured on dedicated lines and subjected to quality control by PCR/ELISA offer sufficient reliability to guarantee the absence of cross-contamination (Olivry 2017).

12.3 — Dedicated Veterinary Foods: Quality Control by PCR on Each Batch

Dedicated veterinary therapeutic foods for EDTs are distinguished by specific manufacturing protocols: dedicated production lines or lines cleaned according to validated procedures, quality control by PCR and/or ELISA on each batch before delivery, complete traceability of raw materials. The principal brands integrate these controls into their manufacturing process, achieving compliance ratings in internal quality audits.

12.4 — Comparative Table: Home-Prepared vs Industrial Therapeutic vs OTC

The choice between a home-prepared diet and an industrial therapeutic diet depends on the clinical situation, owner compliance, and logistical constraints. The home-prepared diet offers absolute certainty of composition but requires strict compliance and nutritional supplementation. The industrial therapeutic diet offers complete nutritional balance and ease of use but carries a residual risk of cross-contamination. OTC foods, with a contamination rate of 27 to 54%, are prohibited for any diagnostic EDT.

PART VII — THE DIFFERENT TYPES OF INDUSTRIAL HYPOALLERGENIC DIETS

Chapter 13 — Novel Protein Diets

13.1 — Fundamental Principle: Individual Immunological Novelty

The principle of novel protein diets rests on immunological novelty: an animal cannot develop an allergic reaction to a protein to which its immune system has never been exposed. This notion is individual and contextual: a protein considered “novel” for one animal may be a common allergen for another.

Lamb, long considered a hypoallergenic protein, no longer fulfils this criterion in 2026 due to its frequent presence in mainstream kibble and wet foods. Similarly, salmon and duck, once considered rare proteins, have become common ingredients in mainstream ranges, reducing their utility as “novel” proteins.

Recommended protein sources in 2026 include venison, kangaroo, rabbit, quail, capelin, pollock, trout, and goat. These proteins remain relatively rare in mainstream commercial formulations and offer a high probability of immunological novelty for most animals.

13.2 — Cross-Reactivities to Anticipate During Selection

Cross-reactivities between taxonomically related species must be anticipated during selection: a dog sensitised to beef presents a risk of cross-reactivity with lamb and venison (Ruminantia), and a dog sensitised to chicken will probably react to duck and turkey (Galliformes/Anseriformes), with an IgE cross-reactivity rate of 97% between chicken and duck (Olivry 2017). This cross-reactivity is documented for specific proteins and reflects molecular homologies between taxonomically related species, without necessarily extending to all proteins of these species.

13.3 — Limitations: Increasing Difficulty in Finding a Virgin Source

The increasing difficulty of finding a “virgin” protein source — owing to the diversification of commercial food formulations and the presence of undeclared animal by-products — constitutes a major limitation of this approach. A recent article by Villaverde (2024) underlines that detailed analysis of the animal’s dietary history has become more complex as brands multiply recipes based on exotic proteins. Insect proteins (Hermetia illucens, Tenebrio molitor), often presented as novel hypoallergenic proteins, cannot be considered as such in atopic animals sensitised to mites, owing to the documented IgE cross-reactivity via tropomyosin (Majewski 2021). However, the clinical demonstration that insect ingestion provokes a dietary cutaneous exacerbation in dogs or cats sensitised to mites remains to be established by controlled provocation studies. In the current state of evidence, the use of insects as a protein source in an EDT therefore warrants a degree of caution, and prior assessment of the animal’s allergic status with regard to mites.

Chapter 14 — Technology and Value of Hydrolysed Protein Diets

14.1 — Biochemical Principle of Enzymatic Hydrolysis

Enzymatic hydrolysis of dietary proteins consists of controlled cleavage of peptide bonds by proteases (trypsin, chymotrypsin, papain), reducing the molecular weight of the resulting peptides. The degree of hydrolysis, defined as the percentage of cleaved peptide bonds, determines the molecular weight distribution of the produced peptides and, consequently, the residual allergenic potential of the formulation.

The critical molecular weight threshold below which a peptide can no longer simultaneously cross-link two adjacent membrane-bound IgE molecules lies at approximately 5 kDa (Cave 2006). Below this threshold, the peptide cannot bridge IgE fixed to FcεRI receptors on mast cells, preventing degranulation and the release of inflammatory mediators.

IgE cross-linking requires an allergen to possess at least two epitopes 5 to 10 nm apart, capable of simultaneously binding to two adjacent IgE molecules on the mast cell membrane. A peptide of less than 5 kDa (approximately 40-45 amino acids) can contain only a single functional epitope, rendering this cross-linking physically impossible. This physicochemical property constitutes the rational foundation of hydrolysed diets.

Standard hydrolysis produces peptides of less than 13 kDa, whilst extensive hydrolysis achieves molecular weights below 1-3 kDa. The study by Olivry et al. (2017) showed that extensively hydrolysed poultry feathers (95% of peptides ≤1 kDa) induced no IgE recognition in the 40 dogs and 40 cats tested, whilst poorly hydrolysed feathers generated a positive IgE response in 37% of dogs. The clinical difference is therefore directly correlated with the degree of hydrolysis.

Bizikova and Olivry clinically confirmed that the extensively hydrolysed feather-based diet did not provoke a pruritic flare in chicken-allergic dogs (0/10 dogs), whilst the hydrolysed chicken liver diet induced a recurrence in 40% of subjects (4/10, p=0.04) (Bizikova 2016). Lewis et al. recently compared in a triple-blind randomised crossover multicentre trial a hydrolysed salmon diet (78.2% of peptides ≤2 kDa) with a hydrolysed feather diet, without significant difference in efficacy between the two formulations (p=0.516 for PVAS, p=0.325 for CADESI-04) (Lewis TP 2025).

14.2 — Persistence of Residual Allergenicity: The Risk of Incomplete Hydrolysis

The persistence of residual allergenicity constitutes the principal limitation of hydrolysed diets. Incomplete hydrolysis (residual molecular weight >5-10 kDa) maintains peptides capable of cross-linking membrane-bound IgE and triggering mast cell degranulation. This phenomenon explains the failures reported with certain commercial hydrolysed diets whose degree of hydrolysis is insufficient.

Masuda et al. (2020) demonstrated that 28.8% of canine sera showed detectable T lymphocyte stimulation in response to hydrolysed diet extracts, confirming that hydrolysis, even when extensive, does not completely suppress T-cell immunogenic potential. Peptides of 1-3 kDa still contain sufficient T epitope sequences to activate CD25low T lymphocytes, a pathway independent of IgE cross-linking.

14.3 — Disadvantages of Food Hydrolysates

Palatability represents an additional challenge: hydrolysis generates small peptides with a bitter taste (due to exposure of hydrophobic residues — leucine, valine, phenylalanine), which may reduce the animal’s acceptance of the diet. Palatability varies according to the protein source (soya and poultry feathers generate different taste profiles) and the degree of hydrolysis (the more extensive the hydrolysis, the more pronounced the bitterness).

Hypo-osmotic diarrhoea, linked to the influx of water into the intestinal lumen provoked by the high osmotic load of small peptides and free amino acids, constitutes a transient side effect (1 to 2 weeks) managed by the addition of soluble fibres (sugar beet pulp, psyllium) to the formulation. This phenomenon must not be confused with a sign of food intolerance to the diet itself.

14.4 — Major Advantage: Implementation Independent of Dietary History

The major advantage of hydrolysed diets lies in their applicability independent of dietary history: regardless of the diversity of previously ingested proteins, extensive hydrolysis theoretically reduces the risk of reactivity. This property makes them the option of choice in animals with complex or unknown dietary history, and constitutes a valuable aid for the practitioner faced with an animal that has consumed multiple ranges of kibble.

14.5 — Prospective Randomised Crossover Multicentre Study

The study by Lewis et al. (2025), involving 57 pruritic dogs distributed across 7 centres, constitutes the first prospective triple-blind randomised crossover multicentre study comparing two hydrolysed formulations (salmon vs poultry feathers). The results show equivalent diagnostic efficacy of both formulations, with a CAFR diagnosis rate of 44.7% (21/47 dogs having completed the study). This study reinforces the validity of hydrolysed diets as a first-line diagnostic tool in industrial EDTs.

Chapter 15 — Elemental Diets Based on Free Amino Acids

15.1 — Definition and Concept: Total Absence of Intact Proteins or Peptides

Elemental diets based on free amino acids represent the most advanced form of dietary hypoallergenicity. These formulations contain no intact protein or residual peptide: the nitrogen source consists exclusively of synthetic amino acids, devoid of any epitope liable to be recognised by IgE or T lymphocytes.

Free amino acids, with a molecular weight between 75 and 204 Da, are too small to constitute a conformational epitope (minimum 1-2 kDa) or sequential epitope (minimum 8-15 amino acids). Consequently, IgE-mediated and T-cell allergenic potential is theoretically nil, conferring on these diets the status of maximum hypoallergenicity standard.

Studies conducted in canine chronic enteropathies and data from Freiche et al. (2025) have shown the efficacy of these diets in dogs refractory to conventional hydrolysed diets, with a clinical response rate of 76% on the CCECAI score. These results support the use of elemental diets as a last-line therapeutic tool in complex cases.

15.2 — Indications: Failures of Conventional Hydrolysed Diets

The principal indications remain repeated failures of hydrolysed and novel protein diets, severely poly-allergic animals, and cases where the dietary history is entirely unknown. These situations, representing approximately 10 to 15% of EDTs in specialist practice, justify recourse to an elemental diet despite its constraints.

15.3 — Limitations: High Cost and Palatability

Limitations include high cost (2 to 3 times the price of a standard hydrolysed diet), sometimes insufficient palatability (requiring progressive transition and strategies to encourage food intake), and use reserved for refractory cases owing to these constraints. Reduced palatability is explained by the taste profile of free amino acids, which differs from that of peptides or intact proteins.

PART VIII — PLACE OF NESTLÉ PURINA DIETS IN INDUSTRIAL ELIMINATION

Chapter 16 — Purina Pro Plan HA Hypoallergenic Diets in Industrial EDTs

16.1 — Positioning of Purina Pro Plan HA in the Industrial EDT Range

Purina Pro Plan Veterinary Diets HA (Hypoallergenic) is positioned within the industrial EDT range as a single-source hydrolysed protein diet. The Purina HA range is distributed exclusively through veterinary channels, ensuring medical supervision of the diagnostic protocol.

The canine formulation rests on a hydrolysed soya isolate as the sole protein source, associated with purified maize starch as the carbohydrate source. Soya constitutes a distinctive choice in so far as this legume is rarely implicated as a major allergen in dogs and cats, although soya sensitisations are documented in approximately 6% of confirmed cases in dogs.

The announced degree of hydrolysis reaches a molecular weight below 11 kDa for the majority of peptides. This threshold lies above the 5 kDa threshold (Cave 2006) but below 13 kDa, placing Purina HA in the category of standard to moderate hydrolysis, distinct from the extensive hydrolysis (<1-3 kDa) offered by Royal Canin Anallergenic.

16.2 — Purina Pro Plan Feline HA (HA St/Ox): Formulation Specificities

The feline formulation (HA St/Ox) incorporates additional urinary health management features (control of struvite and oxalate saturation), adapted to the specific needs of cats. Taurine and arachidonic acid intake is adjusted to meet the requirements of the obligate carnivore, and the quality of the hydrolysed protein source is adapted to feline palatability.

16.3 — Advantages of Purina HA Diets in Clinical Practice

The advantages of Purina HA diets in clinical practice include the presence of a single protein source (hydrolysed soya), a purified carbohydrate (maize starch), and high digestibility favourable to the comfort of the animal’s digestive system. The high digestibility (>90%) contributes to a reduction in colonic fermentation and improves stool consistency, a parameter appreciated by owners in daily life.

Quality control rests on manufacturing protocols including cleaning of production lines between manufacturing runs and traceability of raw materials. Purina protocols provide for regular analyses on finished batches, limiting the risk of cross-contamination by undeclared proteins.

PART IX — FELINE SPECIFICITIES AND DIFFERENCES BETWEEN DOGS AND CATS

Chapter 17 — Differences in Conducting an Elimination Diet in Dogs and Cats

17.1 — The Cat Is an Obligate Strict Carnivore

The cat is a strict carnivore whose nutritional needs differ from those of the dog. Protein needs are 1.5 to 2 times higher (minimum 26 g/100 g dry matter versus 18 g in dogs), and certain essential nutrients cannot be synthesised by the feline metabolism: taurine (indispensable for cardiac and retinal function), arachidonic acid (omega-6 fatty acid derived from animal sources), niacin, and preformed vitamin A.

A vegetarian diet is strongly discouraged in cats due to these foreseeable deficiencies. The absence of taurine leads within 4 to 12 weeks to dilated cardiomyopathy and irreversible retinal degeneration. The absence of preformed arachidonic acid compromises prostaglandin synthesis and platelet function. These metabolic constraints require that any feline elimination diet contain an animal protein source.

Food neophobia is a frequent behaviour in cats, documented in the feline nutrition literature, which constitutes a significant obstacle to the implementation of elimination diets. Its exact prevalence in the context of EDTs has not been specifically quantified. A progressive transition over 7 to 10 days and adaptation of texture are recommended to encourage acceptance of the new regimen, by mixing increasing proportions of the new diet with the previous food (days 1-2: 25/75; days 3-4: 50/50; days 5-7: 75/25; days 8-10: 100%). Acceptance is improved by gentle warming of the food and the choice of a texture adapted to individual preferences.

17.2 — Major Risk Specific to Cats

The major risk specific to cats is hepatic lipidosis, a potentially fatal acute hepatic steatosis that occurs following prolonged fasting or food refusal beyond 48 to 72 hours, particularly in obese cats. Monitoring food intake constitutes a critical parameter in cats: any food refusal exceeding 48 hours necessitates discontinuation of the diet and return to the previous food whilst awaiting an alternative strategy.

17.3 — Alternative Strategies in Case of Refusal: Change of Presentation (Kibble vs Wet Food)

In cases of food refusal, several strategies may be considered: change of presentation (switching from kibble to wet food or vice versa), gentle warming of the food to release its aromas. The diversity of presentations available in therapeutic ranges facilitates adaptation to the individual preferences of the cat.

17.4 — Similar Response Kinetics in Dogs and Cats but Feline Particularities

The response kinetics to the elimination diet are comparable between dogs and cats (6 to 12 weeks), with a minimum recommended duration of 8 weeks in both species. Feline particularities include a higher proportion of digestive signs (40-50% vs 20-30% in dogs), a risk of hepatic lipidosis absent in dogs, more frequent food neophobia, and the absolute necessity of meeting taurine and arachidonic acid requirements.

PART X — CAUSES OF FAILURE, LONG-TERM MANAGEMENT, AND PERSPECTIVES

Chapter 18 — Causes of EDT Failure and Complicating Factors

18.1 — Cause No. 1: Owner Non-Compliance (Flavoured Medications, Treats, Outdoor Access)

Owner non-compliance represents the most frequent cause of EDT failure and must be systematically reassessed in cases of apparent failure. Sources of protocol deviation include unidentified flavoured medications (palatable tablets containing chicken or beef proteins as an excipient), treats given by third parties, and access to another animal’s food.

18.2 — Cause No. 2: Cross-Contamination of the Commercial Food Used

Cross-contamination of the commercial food used constitutes the second cause of failure. Recent PCR data show that most OTC foods contain undeclared proteins (Ricci 2018, Kępińska-Pacelik 2023). Switching to a veterinary therapeutic food manufactured on a dedicated line may resolve this type of failure.

18.3 — Cause No. 3: Uncontrolled Concomitant EAD Simulating Failure

Uncontrolled concomitant EAD may simulate diet failure by maintaining pruritus independently of the food component. The addition of a treatment targeting the environmental component (oclacitinib, lokivetmab) allows discrimination between the two components and reveals partial improvement attributable to dietary exclusion.

18.4 — Cause No. 4: Residual Allergenicity of Hydrolysates

The residual allergenicity of hydrolysates, estimated at 25-40% of dogs according to Masuda (2020) data, explains failures observed with certain hydrolysed diets of insufficient degree of hydrolysis. Switching from a standard hydrolysed diet (<13 kDa) to an extensively hydrolysed diet (<1-3 kDa), home-prepared, or elemental may resolve this type of failure.

18.5 — Cause No. 5: Insufficient Duration (<8 Weeks)

Insufficient duration (<8 weeks) is an avoidable cause of failure. It should be recalled that 10% of responders only show improvement between weeks 8 and 12 (Olivry 2015). A prematurely terminated EDT may erroneously lead to exclusion of the CAFR diagnosis.

18.6 — Algorithm for Resolution of Apparently Failed EDTs

The algorithm for resolution of an apparently failed EDT comprises five sequential steps: verification of compliance (detailed history of everything the animal has ingested), treatment of residual secondary superinfections, dietary change (switching from a hydrolysed diet to a novel protein diet or vice versa, switching to an elemental diet), addition of an antipruritic treatment targeting the environmental component, and extension of duration to 12 weeks.

Chapter 19 — Long-Term Feeding After Diagnostic Confirmation

19.1 — Permanent Avoidance of Identified Allergens

Permanent avoidance of the allergens identified by individual provocation challenges constitutes the nutritional imperative of long-term management. This avoidance must be absolute and definitive: re-introduction, even occasional, of an identified allergen provokes clinical recurrence within 2 to 14 days in the majority of cases (Olivry 2020).

19.2 — Strategy Without Individual Provocations with Maintenance of the Remission Diet

When individual provocations have not been carried out (by owner refusal or clinical choice), maintenance of the remission diet constitutes the default strategy. The animal continues the same elimination diet that led to clinical improvement, without any attempt at re-introduction.

Periodic monitoring every 6 to 12 months is recommended, comprising a biochemical profile (serum protein, lipid profile), assessment of coat and skin quality, and monitoring of weight and general vitality. This monitoring aims to detect early any nutritional deficiency, new sensitisation, or clinical recurrence.

The risk of neo-sensitisation to the maintenance diet protein is biologically plausible and reported anecdotally in specialist clinical practice, but its exact prevalence has not been quantified by published longitudinal studies. Periodic clinical monitoring (every 6 to 12 months) is recommended to detect any recurrence of signs that may indicate a new sensitisation.

19.3 — Rotation of Protein Sources: Empirical Strategy, Non-Robust Data

Rotation of protein sources, although proposed empirically, rests on no robust clinical data and cannot be recommended as a prevention strategy validated by evidence. Preventing sensitisation by varying exposures is contradicted by the absence of controlled prospective studies. Maintenance of a single diet proven to be effective remains the safest strategy in the current state of knowledge.

PART XI — Conclusion

The management of cutaneous adverse food reactions in dogs and cats rests on a rigorous diagnostic approach of which the elimination diet constitutes the cornerstone.

The advances of recent years — molecular characterisation of allergens, development of extensively hydrolysed diets (<1-3 kDa), prospective randomised multicentre studies comparing hydrolysed formulations (Lewis TP 2025) — have strengthened the scientific basis of this approach without modifying its fundamental principle: only strict dietary exclusion followed by provocation challenge permits a definitive diagnosis. Cross-contamination of commercial foods, documented by recent PCR analyses (Ricci 2018, Kępińska-Pacelik 2023), demands constant vigilance in the choice of the elimination food and favours veterinary therapeutic diets manufactured on dedicated lines. Data from Masuda et al. (2020) on residual T lymphocyte stimulation by hydrolysates (28.8% positive responses) raise the question of optimising hydrolysis processes to neutralise both IgE reactivity and T-cell reactivity.

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