Food Allergy

Food allergy is an adverse response of the immune system to a food protein, in which a normally harmless food component is treated as a threat. The most clinically important form is IgE-mediated, in which specific IgE antibodies trigger rapid reactions ranging from hives and swelling to life-threatening anaphylaxis. It differs from food intolerances, such as lactose intolerance, which do not involve the immune system, and from non-immune reactions to food additives or contaminants. Because it is a public health concern in many countries, with prevalence that appears to have risen in recent decades, food allergy has a significant effect on children, families, schools, and emergency care services.

This entry explains how food allergy develops, from the immune basis of sensitization and the classification of IgE-mediated, non-IgE-mediated, and mixed reactions to the way immune tolerance to food is normally established and lost. It then covers which foods cause the most reactions, how common the condition is and what raises the risk, what symptoms look like, and how the condition is diagnosed. The final sections address current treatment, including the limits of avoidance, prevention strategies, and the unresolved questions that drive ongoing research.

Definition and classification

Definition and scope

Food allergy is an immunologically mediated adverse reaction to food proteins. The immune system treats a harmless dietary protein as a threat and responds in a reproducible way each time the food is eaten. This separates it from food intolerance, which arises from digestive, metabolic, or pharmacological mechanisms, such as lactose malabsorption or reactions to histamine-rich foods. It also differs from toxin-induced illness, such as bacterial food poisoning or ingestion of natural plant toxins, which does not depend on prior sensitization. Celiac disease is an immune-mediated enteropathy triggered by gluten and is usually classed separately. Some definitions nonetheless include it among immune-mediated food reactions, so the boundary is not uniformly drawn.

IgE-mediated, non-IgE-mediated, and mixed reactions

Clinicians divide immune-mediated food reactions into three groups. IgE-mediated reactions depend on food-specific antibodies of the IgE class acting on mast cells and basophils, and symptoms usually appear within minutes to about an hour after eating. Non-IgE-mediated reactions are driven mainly by T cells and other cell-mediated pathways, and symptoms typically emerge hours later, most often in the gastrointestinal tract. Mixed reactions involve both pathways. Eosinophilic gastrointestinal disorders, including eosinophilic esophagitis, are the standard example: they are considered allergic because they involve sensitization, even though an IgE-mediated reaction is not always demonstrable.

The three-way split is retained because it guides testing, prognosis, and treatment. IgE-mediated allergy can be investigated with skin tests and serum IgE measurements, whereas non-IgE disorders are diagnosed largely on clinical grounds and, in some cases, histology. The biology is less tidy than the categories suggest. Cellular and antibody responses overlap in most immune reactions, sensitization can occur without any clinical reaction, and the same food may produce different patterns in different patients. The classification is best understood as a practical framework rather than a precise description of mechanism.

Place within the hypersensitivity framework

Allergy is one form of hypersensitivity, an exaggerated or misdirected immune response to a foreign antigen. Type I hypersensitivity is the immediate, IgE-dependent form, and it is the mechanism behind IgE-mediated food allergy. The same type underlies the atopic disorders, including atopic dermatitis, allergic asthma, allergic rhinitis, and allergic conjunctivitis, as well as anaphylaxis and urticaria. "Atopy" describes a predisposition to produce IgE responses to ordinary environmental antigens, while "allergy" refers to the clinical disease that results.

Food allergy is closely linked to these conditions through the atopic march, a proposed sequence in which eczema often appears in infancy, food allergy frequently develops alongside or after severe eczema, and asthma and allergic rhinitis tend to follow in childhood. Children with food allergy have a higher risk of later asthma and rhinitis than children without it, but this association does not establish that one condition causes the other. Shared genetic predisposition, skin barrier defects, and early immune development are all considered possible contributors.

Convincing versus self-reported food allergy

Self-report substantially overstates the number of people with clinically meaningful food allergy. In a large 2015–2016 US adult survey, about 19% reported at least one food allergy, yet the estimate of convincing food allergy was 10.8%. In children, caregivers reported 11.4% prevalence, compared with 7.6% for convincing food allergy. A "convincing" food allergy requires that the symptoms reported after eating a specific food are consistent with an IgE-mediated reaction, judged against a stringent list of symptoms. Reactions that stem from oral allergy syndrome, intolerance, or other non-IgE-mediated causes are excluded. Clinician-diagnosed convincing cases were smaller still, at about 5.1% of adults and 4.7% of children.

Research uses convincing criteria to avoid counting mistaken or misattributed reactions as allergy, which would distort prevalence and risk estimates. In clinical practice, a convincing history marks the starting point for investigation rather than the endpoint. A reported reaction is a hypothesis that requires confirmation through history, testing, and, where appropriate, supervised challenge, because an unverified label can lead to unnecessary dietary restriction.

Common allergens and cross-reactivity

Although more than 160 foods have been recorded as capable of provoking reactions, regulators single out a much smaller group. The nine major food allergens are milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans, and sesame. The first eight were named by FALCPA in 2004; sesame became the ninth through the FASTER Act, effective January 1, 2023. The designation is a legal category, not a purely clinical one, so its boundaries reflect policy as much as biology. Labeling rules also specify the source precisely: name the specific tree nut, fish species, and crustacean shellfish rather than using generic terms. Clams and oysters fall outside the crustacean category in the US.

Regional lists diverge. The European Union includes cereals containing gluten (wheat, rye, barley, oats), crustaceans, eggs, fish, peanuts, soybeans, milk, nuts, celery, mustard, sesame seeds, sulphur dioxide and sulphites, lupin, and molluscs. A product that meets US requirements may therefore still need relabeling for European sale, and other jurisdictions maintain their own schedules.

The dominant allergens also shift with age. The typical foods involved in infants are milk, egg, peanut and probably tree nuts, whereas in older children and adults fruits and nuts are the most frequent allergenic foods. Cow's milk allergy is usually transient: around 90% of children will outgrow the condition by the time they're 3 years old. Egg allergy resolves more gradually, with resolution rates of 4, 26, 48, and 68% of children at ages 4, 8, 12, and 16 years, respectively. Tolerance to baked egg typically arrives earlier than tolerance to raw or lightly cooked egg. Peanut allergy is more persistent, with about 20% of children outgrow it over time. Allergy to milk and egg largely disappears at young age, but can still be present in adults, and peanut and tree nut reactions are more likely to continue into adult life. In registry data from Germany, Austria and Switzerland, among children and adolescents food allergens were the most frequent triggers, comprising 58% of cases. Among these children, legumes (31%) and in particular peanuts were frequently responsible food allergens, followed by tree nuts (25%) with hazelnut being the most frequent elicitor. In adults, fruits (13.4%) most often induced severe food-dependent anaphylaxis, but also animal products (12.2%); among these most frequently crustaceans and molluscs.

Cross-reactivity explains much of the adult fruit and vegetable pattern. The high prevalence of fruit and nut allergy in adults and older children is for a large part due to the pollen-food syndrome: the result of cross-reactivity between allergens in tree (birch) pollen and in fruits, nuts and vegetables. Birch pollen proteins share structural features with proteins in apple, cherry, hazelnut and carrot, so IgE raised against the pollen also recognizes the food. Because many of these food proteins are broken down by heat or digestion, reactions are usually limited to the mouth and throat and cooked versions are often tolerated. This type of allergy is called Oral Allergy Syndrome (OAS) or Pollen-Food Allergy Syndrome (PFAS). Cross-reactivity also operates among related foods: approximately 50% of children who are allergic to one tree nut are allergic to another tree nut.

Less familiar sources include alpha-gal syndrome, which is driven by a carbohydrate rather than a protein. Alpha-gal syndrome (AGS) is a delayed-onset food allergy triggered by an immune response to galactose-α-1,3-galactose (alpha-gal), a carbohydrate associated with Lone Star tick bites. Because humans lack this sugar while most other mammals carry it, it's found in beef, lamb, and pork—all popular protein sources in the human diet. The sensitization route is unusual: when a tick bites a person, it transfers alpha-gal into the bloodstream. Reactions to meat may then be delayed; symptoms typically don't occur for three to six hours after eating red meat. Geographically, Ixodes ricinus in Europe and Ixodes holocyclus in Australia are implicated alongside the US lone star tick. Because the sugar also occurs in dairy products or gelatin, avoidance advice limited to red meat leaves patients exposed. Early cases were recognized in patients given a cetuximab antibody infusion, reflecting IgE directed at the sugar. AGS is likely underdiagnosed because of the unusual presentation of the allergy, historic lack of available testing, and deficiency of physician knowledge about the condition.

IgE-mediated mechanisms

Sensitization

The IgE pathway starts with sensitization, a phase that can pass without any clinical reaction. Sensitization is the state of having detectable food-specific IgE, which can precede clinical food allergy. Food proteins that cross a damaged barrier in the inflamed gut or skin release danger signals, and these signals push dendritic cells toward a pathogen-defense profile (11-6). In the regional lymph nodes, these activated antigen-presenting cells carry allergen to naive T cells and prime them toward a Th2 profile, partly through OX40L DCs upregulate OX40L, priming T cells toward a Th2 cell response.

The Th2 helper cells then supply IL-4, and this cytokine signals B cells to switch their antibody class toward IgE Upon initial sensitization, allergen-specific IgE antibodies are produced by B cells, which pass through a process of class switch recombination regulated by cytokines such as IL-4 and IL-13. The same Th2 cytokines also promote the differentiation of IgE-secreting plasma cells and the proliferation of intestinal mast cells These type-2 cytokines promote B cells differentiation into IgE-producing plasma cells as well as intestinal mast cell proliferation and accumulation known as mastocytosis.

Receptor binding, degranulation, and preformed mediators

Once produced, allergen-specific IgE circulates and binds to high affinity IgE receptors on tissue-resident mast cells and circulating basophils. The receptor involved is FcεRI, and the mast cells and basophils carrying it remain primed without symptoms until the allergen returns. On re-exposure, a single food protein can bridge two neighboring IgE molecules, and this cross-linking causes degranulation within minutes Two adjacent IgE molecules binding to the food protein cause degranulation of the mast cell and basophil followed by preformed mediator release within minutes of exposure. The stored granules release preformed mediators, most prominently histamine, along with platelet-activating factor, prostaglandins and cytokines cross-linking of re-exposed food allergens to allergen-specific IgE that binds to FcεR on mast cells induces degranulation of mast cells and release of several kinds of mediators such as histamine, platelet-activating factor (PAF), prostaglandin, and cytokines.

Newly synthesized mediators and the late phase

Activation also triggers the rapid manufacture of new mediators. Antigen-induced crosslinking of IgE antibodies bound to this receptor results in the release of potent, preformed inflammatory mediators contained in granules, the rapid synthesis of eicosanoids, and the de novo production of type 2 inflammatory cytokines. Eicosanoids include leukotrienes and prostaglandins, which extend the inflammatory response beyond the initial burst. Mast cells and basophils can also act as sources of IL-4 and IL-13 themselves, which feeds back into Th2 polarization Basophils and mast cells, in addition to their roles driving type I hypersensitivity reactions, can also function as innate sources of Th2 cytokines similar to the role of ILC2s. In the later phase, eosinophils cooperate with mast cells, and their toxins and cytokines sustain the inflammation Eosinophils cooperate with mast cells to produce an allergic response through their toxin and cytokine release upon activation that constitute the late-phase response. Repeated ingestion can also expand the mucosal mast cell population, since IL-4 signaling provided by CD4+ TH2 cells induces emigrated mast cell progenitors to become multi-functional IL-9-producing mucosal mast cells, which then expand greatly after repeated food ingestions.

Organ-specific reactions, route, and dose

Because mast cells sit in many tissues, one mechanism can produce symptoms in several organs. Mast cells reside in the skin and mucosal tissues where they are among the first cells of the immune system to interact with foreign antigens. Typical food reactions appear within 2 hours of ingestion, and can affect single or multiple organ systems, including the skin (hives), the respiratory tract (bronchoconstriction, cough), and the gastrointestinal tract (nausea, vomiting, diarrhea). Mouse studies suggest that different mast cell subsets account for different patterns: systemic anaphylaxis was uniquely associated with activation of connective tissue mast cells and release of histamine, while activation of mucosal mast cells did not correlate with symptoms. Gastrointestinal symptoms, by contrast, track more closely with mucosal activation, and gastrointestinal manifestations of food allergy were associated with an increase of MMCP-1-expressing mast cells in the intestine, and evidence of both mucosal and connective tissue mast cell activation.

The route of first exposure matters. Clinical observations suggest that patients who develop severe allergic reactions to food are often sensitized through the skin in early infancy. Dose also shapes outcome, although its role is complicated. In mice, a positive correlation between systemic antigen dose and severity of systemic anaphylaxis has been reported, and whether an allergen causes anaphylaxis depends on how quickly it reaches the circulation as well as its concentration The involvement of the IgE or IgG pathways in anaphylaxis is dependent on the concentration of antigen that enters the systemic circulation following oral or parenteral antigen challenge and the rate with which it accesses IgG-bearing macrophages/basophils or IgE-bearing mast cells. In clinical practice, however, the amount of allergen which provokes a reaction cannot predict the severity of the reaction or the likelihood of anaphylaxis. Exactly where food antigens cross the intestinal epithelium to engage IgE on mast cells also remains unresolved It is still not clear where eliciting food allergens traffic across the epithelial barrier of the GI tract to drive IgE crosslinking.

Non-IgE-mediated and mixed reactions

Not every adverse reaction to food is driven by IgE antibodies. Non-IgE-mediated reactions depend mainly on cellular immunity, so they tend to be slower and more diffuse than classic reactions. Their symptoms often appear hours after eating rather than within minutes, and the gastrointestinal tract is the main target. Mixed reactions combine both pathways. The biology is incompletely understood, and the clinical categories are partly a practical convention.

Infant enterocolitis, proctocolitis and enteropathy

The best-described non-IgE disorders in the gut are food protein-induced enterocolitis syndrome (FPIES), food protein-induced allergic proctocolitis (FPIAP) and food protein-induced enteropathy (FPE). These conditions are thought to form a continuum, with the clinical picture determined by which segment of the gut is inflamed. FPIES presents with repeated, often forceful vomiting and can produce dehydration, lethargy and pallor, sometimes progressing to shock. It is seen mainly in infants, and cow's milk protein is a frequent trigger. Its mechanism is debated: some accounts emphasize T-cell-driven inflammation, while others point to innate immune activation.

FPIAP is the milder counterpart. It typically causes visible blood in the stool of an otherwise healthy, thriving infant, and it usually resolves by early childhood. In the largest prospective infant cohort cited in the literature, the cumulative incidence was about 0.34% for FPIES and about 0.16% for FPIAP, and both figures are considered underestimates. FPE is characterized by more chronic, diffuse intestinal disturbance. Acute FPIES episodes are treated with rehydration and, when needed, antiemetics, whereas FPIAP generally requires no acute treatment. Long-term management of both is avoidance of the trigger food.

Dermatitis herpetiformis

Dermatitis herpetiformis (DH) is usually discussed alongside food reactions because it is triggered by dietary gluten, but it is an autoimmune condition rather than a classic food allergy. It is regarded as the skin expression of celiac disease. Patients develop an intensely itchy, blistering rash, most often on the elbows, knees, buttocks and scalp. Immunoglobulin A (IgA) directed against epidermal transglutaminase (TG3) is deposited in the papillary dermis, and this granular pattern is the key diagnostic finding on skin biopsy with direct immunofluorescence. Most patients also have small-intestinal changes, although intestinal symptoms are often mild or absent. Nearly all carry the HLA-DQ2 or HLA-DQ8 genotype, and a strict gluten-free diet controls both skin and gut disease, while dapsone is commonly used for the rash.

Eosinophilic esophagitis and mixed reactions

Eosinophilic esophagitis (EoE) is a chronic inflammatory disease of the esophagus, characterized by eosinophil-rich infiltration of the mucosa. It is generally regarded as a food-driven disorder with a predominantly Th2-type response, and it is classified as mixed when IgE-dependent and non-IgE pathways are both involved. Its prevalence is markedly higher among people with IgE-mediated food allergy, and dairy, wheat, egg and soy are among the most frequently implicated foods. Elimination diets produce histological and symptomatic remission in most patients, and symptoms and eosinophilia tend to recur when the foods are reintroduced. Some authorities still list EoE with the non-IgE disorders, which illustrates how the classification remains contested.

Diagnostic challenges

The non-IgE and mixed conditions share a diagnostic problem: there are no reliable blood or skin tests. Skin prick tests, serum IgE tests and patch tests do not reliably identify EoE triggers, and the diagnosis of FPIES and FPIAP rests on clinical history. Typically, symptoms improve after the suspect food is removed and return on reintroduction, which is ideally documented under medical supervision. Delayed onset makes it hard to link symptoms to a specific food, and symptoms overlap with reflux, colic and common infant rashes, which can delay recognition.

EoE requires upper endoscopy with biopsy. The histological threshold is usually more than 15 eosinophils per high-power field in any sample, after other causes of eosinophilia are excluded. The mucosa can look normal in roughly a quarter of patients, so biopsy is needed even when the endoscopic appearance is unremarkable. Because the disease is patchy, sampling matters: guidelines recommend at least six biopsies, and diagnostic sensitivity has been reported to rise from about 55% with a single biopsy to nearly 100% with five or more.

Immune tolerance and its failure

Under normal conditions the gut immune system does not attack dietary proteins. Oral tolerance is a type of peripheral tolerance that implies the non-responsiveness to ingested food proteins. In this sense it is a special case of immune tolerance that operates in the periphery, outside the thymus. Several overlapping routes keep responses to harmless food antigens in check. Deletion, anergy and ignorance are mechanisms that the immune system employs to maintain oral tolerance through cell death or functional unresponsiveness of lymphocytes capable of responding to food antigens.

The cells that carry out this control are mainly dendritic cells, intestinal epithelial cells and resident microbes. A subset of CD103+ DCs is capable of inducing T regulatory cells (Treg cells) that express anti-inflammatory cytokines. Tregs suppress effector responses partly through cytokines such as IL-10 and TGF-β, which restrain the proliferation of T cells and modulate macrophages and Th1 and Th2 effector cells. Regulatory B cells contribute as well.

Regulatory T cells are the best-characterised suppressors in oral tolerance, and their stability depends on the transcription factor Foxp3. Loss-of-function mutations in the FOXP3 gene cause the severe multi-organ autoimmune and allergic disorder known as IPEX syndrome, which shows how much human tolerance depends on this pathway. Experimental work points in the same direction. Mice that cannot express Th2 cytokines in their Foxp3+ cells do not develop food allergy. Tregs also appear to be needed to build tolerance, not only to maintain it: children who lost their milk allergy showed higher frequencies of CD4+CD25+ Tregs after allergen challenge. The balance of antigen dose matters too. High-dose results in lymphocyte anergy/deletion. Low-dose results in activation of regulatory T cells. The form of the antigen matters as well, since soluble antigen is more tolerogenic than particulate antigen.

Food allergy is generally framed as a failure of this system. Breakdowns in oral tolerance are thought to open the way to food allergy and to chronic intestinal inflammatory disease. The epithelium is one place where the failure could begin. Enterocytes lack the co-stimulatory signals needed for full T-cell activation, which may make them tolerogenic presenters. Yet some allergens, such as lipid transfer proteins, can cross the epithelium largely intact, so the barrier is not absolute.

The skin is proposed as the second entry point. In the widely accepted dual-allergen exposure model, skin barrier plays an essential role in the pathogenesis of food allergy through its ability to induce epicutaneous sensitization which corresponds to one half of the widely accepted dual allergen exposure hypothesis. Resident skin dendritic cells capture allergens and carry them to draining lymph nodes, where they are presented to naive CD4+ T cells. The discovery that FLG loss-of-function mutations, which have an important role in formation and integrity of the SC, are highly associated with AD and xerosis (dryness), was a major milestone in understanding AD as a "barrier" disease. The evidence linking this barrier defect to food allergy is indirect. In an 18-year birth cohort, the association between filaggrin mutations and food allergy only appeared when patients also developed eczema. That pattern points to eczema-related barrier damage rather than a direct effect of filaggrin on immunity. Experimental sensitization through the skin also tends to need help: in most mouse models of epicutanous sensitization, the SC needs to be mechanically impaired by tape-stripping, patch dressing, or treatment with adjuvant.

Gut microbiota and dysbiosis

The gut microbiome is considered a key input to the tolerance decision. The human microbiome is an essential mediator in the induction of oral tolerance or food allergy. Animal studies support a causal role. Germ-free mice colonized with microbiota from healthy donors are protected against the development of cow's milk allergy. In contrast, colonization of mice with fecal microbiota from children with food allergies did not keep animals away from food allergies, whereas colonization with microbiota belonging to healthy children proved to be defending.

Early colonisation appears to be a sensitive window. In the case of food allergy, various longitudinal or cross-sectional studies have demonstrated fewer challenge-proven or doctor-diagnosed cases in children with siblings or attending childcare before six months. Mode of delivery is one factor that affects the initial inoculum. Infants born by caesarean section are exposed to maternal skin and environmental microbes only, rather than to the vaginal and fecal microbiota. Specific taxa have also been linked to outcome. Children with microbiota profiles which are enriched in tolerance-promoting taxa, such as Bifidobacterium and Clostridia, are more likely to develop immune tolerance and even outgrow early-life food allergies, whereas dysbiotic patterns characterized by dominance of Escherichia-Shigella or depletion of SCFA producers predict persistent food allergy. Whether these associations are causal, and how dysbiosis actually pushes immune maturation toward sensitization, remains unclear. It is unclear how dysbiosis, the change in microbiota composition that leads to disruption of gut homeostasis and eventual disease, affects the immune system in the development of food allergies. Clinical efficacy data for microbiota-directed treatments are also contested.

Timing, route and dose of early exposure

The central question is why most people tolerate food proteins while only a minority become sensitised. Despite a growing literature in the field of food allergy, it is not yet clear why the majority of individuals are immunologically tolerant to food antigens, while few individuals develop allergic sensitization. The current model combines genetics, diet, skin exposure and microbial colonisation. It is now recognized that it is the complex interplay between genetic inheritance, diet, skin exposure and gut microbiome that is crucial to the development of food allergy.

The most influential evidence for timing comes from randomized trials. In the Learning Early About Peanut allergy (LEAP) trial, published in 2015, infants at high risk because of severe eczema or egg allergy who ate peanut early in life had much lower rates of peanut allergy at age five than infants who avoided it, roughly 1.9% versus 13.7%. The findings suggest that the window of early exposure can shape later tolerance, but several questions remain open. Whether the same benefit applies to the general population, to other allergens, or to infants with less skin disease is not fully settled. Whether protection persists after regular consumption stops is less certain. The mechanisms linking early exposure to durable tolerance, including the relative roles of skin and gut routes and the effective dose, are still being studied. Prevention guidelines are discussed in a separate section.

Epidemiology and risk factors

Prevalence and how cases are counted

Prevalence figures for food allergy depend heavily on how a case is defined. In the largest recent U.S. survey, caregivers reported a current food allergy in 11.4% of children, but that figure fell to 7.6% once researchers required a history of symptoms consistent with an IgE-mediated reaction to a specific food. Among adults, about 19% said they had a food allergy, while the convincing-case estimate was 10.8%. The narrowest definition, requiring a clinician diagnosis together with a convincing history, gave 4.7% for children and 5.1% for adults. Among adults, the most frequent convincing allergies were to shellfish (2.9%), milk (1.9%), peanut (1.8%), tree nut (1.2%) and fin fish (0.9%). Earlier national data from 2007–2010 had found a self-reported childhood rate of 6.53%.

Rising prevalence and possible explanations

A meta-regression of twenty CDC surveys covering nearly 400,000 children from 1988 to 2011 estimated that self-reported childhood food allergy rose by about 1.2 percentage points per decade. Other indicators moved faster. Self-reported peanut or tree nut allergy in U.S. children roughly tripled between 1997 and 2008, and claims data show that annual peanut allergy incidence in one-year-olds tripled between 2001 and 2017. Hospitalizations for food-related anaphylaxis have also risen since 1990 in the United Kingdom, the United States and Australia, most sharply in children aged 0–4.

Part of the apparent rise may reflect better recognition and reporting. Parents and physicians are more likely to label a reaction as allergic than they were a generation ago, and some clinical reports indicate that survey-based estimates overstate the true burden even when symptom criteria are applied. Experts have also cited greater awareness as one contributor to the trend. This explanation does not account easily for the rise in serious reactions requiring hospital care, which argues that a real increase in sensitization is also occurring.

Established and proposed risk factors

Family history and atopic disease are the strongest and most consistent associations. A systematic review found that the severity of atopic dermatitis in children strongly influences the likelihood of food allergy. Early food introduction is another well-documented factor. Observational data from the late 1980s and 1990s showed that Jewish children in London, who were largely kept from peanut in infancy, had a roughly tenfold higher prevalence of peanut allergy than Jewish children in Israel, where peanut was introduced earlier and eaten more often. Such comparisons are observational and cannot separate timing from other genetic or environmental differences.

Vitamin D status has been proposed as a factor because food allergy rates appear to increase with distance from the equator, where sunlight is weaker. The evidence on whether vitamin D insufficiency causes food allergy remains inconclusive. Urban and industrialized lifestyles are often discussed alongside these ideas, since they are linked to altered microbial exposure and diet. Dietary fat intake and obesity have also been proposed as contributors, but their roles are less clearly established and are still debated.

The multi-allergy problem

Many food-allergic people react to more than one food. In the 2015–2016 U.S. survey, about 40% of food-allergic children and 46% of food-allergic adults had convincing allergies to multiple foods. Analysis of the same data identified recurring patterns: milk with egg, seafood, peanut with tree nut, and a broadly multi-allergic group. Sensitization is also asymmetric; for example, 61% of children with a tree nut allergy were also allergic to peanut, while only 33% of peanut-allergic children were allergic to tree nut. Multiple allergies carry a higher clinical burden, including more emergency visits, and the higher number of allergies tends to track with greater risk of severe reactions.

Multi-allergy complicates management in practical ways. Patients often avoid more foods than their diagnosis requires, which can narrow diets and affect nutrition and quality of life, so a precise diagnosis of each allergy matters. It also complicates immunotherapy, because treatment programs must address several foods at once, and estimates from trial documents suggest that roughly 30% to 60% of food-allergic patients are allergic to multiple foods.

Clinical features and severity

Symptoms of an IgE-mediated food reaction reflect where mast cell and basophil mediators act. Histamine and leukotrienes increase vascular permeability, contract smooth muscle, and stimulate nerve endings, so the same process can appear as itching, hives, or swelling in the skin, cramping and vomiting in the gut, wheezing in the airway, and a fall in blood pressure in the circulation. Typical cutaneous signs include urticaria and angioedema of the lips, face, or tongue. Gastrointestinal signs include vomiting, diarrhea, nausea, and abdominal pain. Respiratory involvement ranges from throat tightness and cough to wheezing and shortness of breath. Cardiovascular involvement can progress to dizziness, fainting, and circulatory collapse.

Onset time is a practical guide to mechanism. Reactions mediated by IgE usually begin within minutes and most within about two hours of ingestion, whereas delayed reactions that appear hours later point toward cell-mediated or mixed pathways, which tend to affect the gut more than the skin or airway. Symptoms that start late or evolve over the day can also reflect a cofactor or a food that was eaten in a large amount.

Anaphylaxis

Anaphylaxis is a rapidly progressing, potentially fatal systemic reaction. The widely used clinical criteria, originally proposed by a NIAID and FAAN panel in 2006, require one of three patterns: acute onset with skin or mucosal involvement plus respiratory compromise or reduced blood pressure; two or more organ systems involved after exposure to a likely allergen; or reduced blood pressure after exposure to a known allergen. Severity is often graded with the Sampson scale, which runs from mild skin symptoms to cardiorespiratory arrest.

Food is the leading identified trigger of anaphylaxis among children seen in United States emergency departments. A national claims analysis covering 2005 to 2014 found that such visits rose by 214 percent over the period, with the highest rates in infants and toddlers, and peanut was the most frequent culprit. A New York City pediatric emergency department series likewise found food responsible for most identified triggers, while also noting that the ICD code for anaphylaxis was underused. Epinephrine delivery is a recurring gap: in one urban series, about a quarter of reactions had been treated with epinephrine before arrival, and in a Tokyo cohort only about a quarter of children weighing under 15 kg with a prior food anaphylaxis history held an auto-injector.

Factors that determine severity

Severity depends first on the dose of allergen. Each person has an individual eliciting threshold, the lowest amount that provokes objective symptoms, and this threshold varies widely among patients and over time. Cofactors modify the picture. Exercise, nonsteroidal anti-inflammatory drugs, alcohol, and, in some studies, sleep deprivation can lower the threshold or increase severity. In wheat-dependent exercise-induced anaphylaxis, for example, a controlled oral challenge in one series of 71 patients elicited reactions at rest in 37 percent, and treadmill exercise markedly lowered the eliciting dose. Cofactors appear in a substantial proportion of food anaphylaxis cases, though estimates differ widely; at the population level, their effect on threshold distributions may be modest. Pre-existing asthma and the use of beta blockers are associated with more severe reactions, and an unrecognized trigger or a high-risk initial presentation can be associated with a more protracted course.

Biphasic reactions and follow-up

A biphasic reaction is a recurrence of anaphylactic symptoms after initial resolution, without re-exposure to the allergen. Published frequencies vary, with estimates of roughly 1 to 20 percent of anaphylactic episodes and higher rates after severe food reactions, and the second phase has been reported from about 1 to 72 hours later. Risk factors reported in various studies include delayed epinephrine, an initially small dose, an unknown trigger, initial hypotension, and multiple doses of epinephrine. Food triggers have, in one large study, been associated with a lower risk of biphasic reaction than other triggers.

Because of this variability, guidelines advise a minimum observation period of about four hours after resolution, with six to 12 hours or longer for patients with risk factors or a severe initial presentation. A meta-analysis cited in current guidance found that observation for more than six hours after resolution would detect recurrence in more than 95 percent of cases. Prompt intramuscular epinephrine remains the first-line treatment in all cases, and patients who have had anaphylaxis should be prescribed an auto-injector, referred for specialist assessment, and given written instructions on when to use it. Hospital admission rates after food anaphylaxis in children's emergency departments have varied widely between centers, from about 20 to 98 percent in one multicenter study, which suggests that management practice is not yet standardized.

Diagnosis

Clinical history as the starting point

Diagnosis begins with a detailed account of the reaction: which food was eaten, how much, how soon symptoms began, which organ systems were involved, and whether the same food has caused trouble before. Timing is especially informative. IgE-mediated reactions usually appear within minutes to about two hours, while delayed or non-IgE reactions may take hours or longer and tend to affect the gut. Clinical history and lab tests have poor diagnostic accuracy and they cannot make a certain diagnosis of a food allergy. The history therefore has to be weighed against test results rather than read in isolation. Clinicians also need to separate allergy from non-immune reactions. Lactose intolerance and hereditary fructose intolerance rest on well-defined mechanisms and have validated diagnostic tests, whereas many other reported intolerances, such as non-coeliac gluten sensitivity and FODMAP intolerance, are mainly based on patients' reports. Toxin-related illness and pharmacological sensitivities, such as histamine accumulation in spoiled fish, likewise need to be considered before an allergy is assumed.

Skin prick tests and serum allergen-specific IgE

Skin prick testing introduces a small amount of allergen extract into the skin and measures the resulting wheal, while serum tests quantify allergen-specific IgE in the blood. Both are useful mainly for their negative results. Both tests have a good negative predictive value, but their positive predictive value can be as low as 50%, which underlines the importance of testing only for suspected foods identified from a convincing clinical history. Positive results are interpreted using cut-off values, which vary by food and population. In one study of children, a skin prick result of at least 8 mm and a specific IgE of at least 15 kUA/L had predictive values of 95% and 92%, respectively, for a positive challenge. The thresholds are not universal, however. In infants, a wheal of 4 mm or more was the 95% threshold for egg, and 8 mm or greater for sesame, and a Singapore study found that a peanut-specific IgE of 6 kU/L was the appropriate decision point, lower than the value reported in earlier work. The two tests also frequently disagree, so clinicians interpret them together and with the history. Skin prick tests and specific IgE levels are moderately useful for predicting oral food challenge outcomes in patients with cow's milk or hen's egg allergy. Performance is weaker in some groups; in adults with eosinophilic esophagitis, skin testing correlated poorly with immunoblot results for food allergens, with false negatives common for wheat and whole milk.

Oral food challenge as the reference standard

The double-blind, placebo-controlled oral food challenge is the standard against which other methods are judged. The oral food challenge (OFC) is the gold standard for diagnosis of a food allergy. During the procedure, the patient receives increasing amounts of the suspected food under observation. Challenges are suggested to be conducted with semi-logarithmic incremental doses based on the protein content, typically for IgE-mediated food allergy with intervals of 20–30 min between doses. A challenge is judged negative when no signs or symptoms occur during dose administration and for 2 h after ingesting a full portion of the food. Stopping rules are critical, because they reduce the risk of false-positive diagnoses, but also severe reactions.

Because reaction severity cannot be predicted based on SPT or sIgE testing, the procedure carries real risk. Oral food challenges can result in life-threatening anaphylactic reactions, prompting the need for standardized protocols and well-trained allergists and clinical staff. Patients are expected to be well on the day of testing, and allergic conditions, including atopic dermatitis and asthma, should be well-controlled to minimize risk of severe reaction. For this reason challenges are performed in specialist settings with resuscitation equipment and are challenging and expensive to perform. Some data suggest that challenges in young children can be done safely; in one small cohort of 18 infants, the single positive reaction was limited to the skin, although the authors called for larger studies.

Limits of self-report and antibody testing

Self-report is the least reliable starting point. A meta-analysis found that the prevalence of self-reported food allergy was 3–35% compared to 1–10.8% for food allergies diagnosed by a physician and confirmed with a food challenge. A pooled analysis of lifetime figures showed a similar gap, with a pooled lifetime prevalence of self-reported food hypersensitivity of 17.3% but only 2.7% prevalence as confirmed by skin prick tests and 0.9% confirmed by food challenges. In the United States, 19% of adults considered themselves to be food allergic and followed an avoidant diet to alleviate their complaints without seeking a confirmatory medical examination.

Overreliance on antibody tests drives much of this overdiagnosis. Patients with nonspecific symptoms, such as rash or abdominal complaints, who have positive skin prick or serum food-specific IgE results to foods have less than a 50% likelihood of actually having a food allergy, according to researchers who warned of this problem. In one retrospective review of children referred for challenges, 325 of 364 challenges (89%) were negative, a result that highlights how often restrictions were unnecessary. Unneeded elimination carries its own harms, including the risk of nutritional problems from elimination diets (eg, milk or egg elimination in children), significant anxiety and worry, and the social challenges food allergies cause. Growth can also suffer; children on strict elimination diets have been reported to show significantly lower body height and weight as well as a deficiency in nutritional intake compared with peers. Other test types carry the same problem. Food-specific IgG results do not indicate allergy, and a person with true IgE-mediated allergy may very well not have elevated levels of specific IgG to their particular allergen, and may be inappropriately advised to reintroduce this potentially deadly item into their diet. Panel testing of foods that have never caused a reaction is likewise discouraged, because of the risk of misdiagnosis.

Treatment and management

Allergen avoidance

Strict avoidance remains the basis of management. Allergens can appear in sauces, baked goods and processed products under unfamiliar names, so patients and caregivers must read ingredient lists every time they buy a product. Cross-contact, the unintended transfer of trace allergen from one food, surface or utensil to another, is a separate hazard that ingredient labels do not capture; it is limited through dedicated equipment, thorough cleaning and clear communication with food handlers. Eating outside the home is usually the hardest part of avoidance, because restaurants may not track allergens across every dish and a single unlabelled ingredient can trigger a reaction.

Emergency treatment and action plans

Intramuscular epinephrine is the first-line drug for anaphylaxis, and antihistamines do not substitute for it. Anaphylaxis is acutely treated with epinephrine, removal of the allergen, postural changes, and bronchodilator administration. Because reactions can progress quickly, patients are usually prescribed auto-injectors and are advised to carry more than one device. Written action plans specify which symptoms call for which steps. Copies are needed for caregivers, schools and childcare providers, so that staff who did not prescribe the device can recognise a reaction and give it without delay.

Allergen-specific immunotherapy

Oral immunotherapy (OIT) gives gradually increasing doses of a food protein with the aim of raising the amount a person can eat without reacting. Current food allergy treatments, such as oral immunotherapy (OIT) or sublingual immunotherapy (SLIT), must be tailored for patients allergic to individual foods. The only FDA-approved product of this type is peanut-based. The manufacturer describes it as the first and only FDA-approved oral immunotherapy treatment for reducing allergic reactions, including anaphylaxis, in children (1–17 years of age) with peanut allergy. Its purpose is to reduce the severity of reactions, not to produce a state in which the drug is unnecessary, and the labelling states that PALFORZIA does NOT treat allergic reactions and should not be given during an allergic reaction. The risks are substantial. In the trial data, anaphylaxis was reported in 9.4% of PALFORZIA-treated subjects compared with 3.8% of placebo-treated subjects during Initial Dose Escalation and Up-Dosing combined, and most of these reactions began within two hours of a dose. Because of this risk, the product is available only through a restricted program under a Risk Evaluation and Mitigation Strategy (REMS) called the PALFORZIA REMS, patients must be observed after dosing, and it is not given to people with uncontrolled asthma.

Sublingual immunotherapy places allergen drops under the tongue. In one open-label study, only 4 mg of peanut protein resulted in clinically significant desensitization that persisted for multiple months following discontinuation of the therapy, and the rate of side effects in the SLIT study was low, mostly consisting of a mouth itch. Sublingual products for foods remain largely at the trial stage.

Epicutaneous immunotherapy (EPIT) delivers allergen through the skin rather than the mouth. The Viaskin Peanut patch delivers tiny amounts of peanut protein through the skin. An earlier application was rejected by the FDA in August 2020 over whether the patch adhered to the skin consistently enough and whether problems with adhesion could have affected the results. The manufacturer then redesigned the patch. In the earlier open-label extension of the PEPITES study, after three years of using the Viaskin Peanut patch 52 percent of the study population of peanut-allergic children ages 4-11 could consume at least 1,000 milligrams of peanut protein before reacting. The pivotal Phase 3 VITESSE trial enrolled 654 pediatric patients aged 4 to 7, who were randomised 2:1 to active patch or placebo over a 12-month primary period. The company has since submitted a biologics license application and requested Priority Review of the application. The company gave no date for the FDA's response to the priority-review request or for a marketing decision.

Omalizumab and emerging approaches

Omalizumab, a monoclonal antibody, binds free IgE, preventing its interaction with the high-affinity IgE receptor (FcϵRI) on mast cells and basophils, thereby reducing their reactivity and the potential for degranulation upon allergen encounter. On February 16, 2024, the Food and Drug Administration approved omalizumab for the reduction of allergic reactions, including anaphylaxis, that may occur with an accidental exposure to one or more foods in adults and children aged 1 year and older. The approval rested on the OUtMATCH trial, in which 67% achieving the primary outcome compared with 7% of placebo recipients. The primary outcome was tolerating at least 600 mg of peanut protein without dose-limiting symptoms. In a head-to-head second stage, omalizumab was superior to OIT with a success rate of 36% compared to only 19% with OIT. Serious adverse events were less frequent in the omalizumab group, at none compared with 30.5% in the OIT group. A meta-analysis of eight studies found that omalizumab-based therapy significantly increased the likelihood of achieving a clinically meaningful TMD compared to control interventions, while no statistically significant difference was noted in the overall incidence of TEAEs between the omalizumab and control groups. Its limits include high costs, the need for standardized treatment protocols, and limitations related to total IgE thresholds for eligibility. Its effect is also tied to continued use. Follow-up data on durability are still limited, and the open-label extension showed only the durability of this response over 24 weeks.

Other approaches are in development. Research is examining alternative routes of immunotherapy, including sublingual therapy, subcutaneous injections, epicutaneous patches, and recombinant anti-IgE antibodies. Hypoallergenic preparations, in which allergen proteins are modified to reduce IgE binding while retaining the features needed for immune tolerance, are also under study. Food allergy can be managed with these tools, but none of them has yet been shown to remove the underlying sensitization permanently.

Prevention and public health policy

Advice on infant feeding has changed direction over the past two decades. By 2008 the American Academy of Pediatrics had dropped its earlier recommendation to postpone peanut introduction until age three in high-risk children, because delay did not appear to be protective. In 2008, the AAP rescinded prior guidance to delay introduction of peanut to at-risk children until age 3 years, as this strategy was not protective against food allergy. The shift rested mainly on the Learning Early About Peanut Allergy (LEAP) trial. It randomized 640 high-risk infants aged 4 to 11 months to regular peanut-containing foods or to complete avoidance until age five. In an intention-to-treat analysis, 17.2% of the group that avoided peanut developed a positive peanut challenge test at the age of 5 years compared to 3.2% in the group that consumed the food. The follow-up LEAP-On study found that children who ate peanut foods from infancy to age 5 years and then avoided peanuts from ages 5 to 6 years were still 74% less likely to develop peanut allergy than children who had avoided peanut throughout. LEAP enrolled only infants with severe eczema, egg allergy, or both, so this study only included infants considered at high risk for food allergy, and its direct applicability to the general population is less certain.

The evidence for the general population is more modest. The EAT study, which followed breastfed infants, introduced six allergenic foods early. In the intention-to-treat analysis, food allergy to one or more of the six intervention foods developed in 7.1% of the participants in the standard-introduction group and in 5.6% of those in the early-introduction group, a difference that was not statistically significant. A per-protocol analysis, however, favored early introduction, and the authors concluded that the early introduction of all six foods was not easily achieved but was safe. A pooled analysis of LEAP and EAT, covering about 1,550 participants, showed a significant reduction in peanut allergy. Follow-up in other settings has been less consistent. Following the revision of early introduction guidelines in Sweden, introduction of peanut, egg, and other potentially allergenic foods during the first year of life increased; however, no difference in the prevalence of self-reported IgE-FA was observed, and a study in Australia found only a small, non-significant change in peanut allergy prevalence.

Guidelines have followed this evidence in stages. Released in 2015 and 2017, these guidelines initially focused on children thought to be at high risk of food allergy. In 2021, new guidelines support introduction of peanut, egg and other major food allergens at 4-6 months in all children without a history of prior reaction. Adherence remains a practical obstacle. Feeding foods several times a week for years is demanding, and in the case of LEAP, parents were contacted 104 times throughout the study to ensure compliance. Safety data have been reassuring, since infant anaphylaxis is rare, with allergic infants typically presenting with mild to moderate symptoms.

Labeling law is the other main policy lever. In the United States, the Food Allergen Labeling and Consumer Protection Act of 2004 defined eight major allergens, with declaration required from 2006. The FASTER Act amended section 201(qq) of the FFDCA to add sesame as the ninth major food allergen. Manufacturers had until January 1, 2023 to update labels. Allergens may be declared either within the ingredient list or in a separate "Contains" statement. Specific tree nut variety and fish or shellfish species must be named; generic "nuts" or "fish" is not compliant. The FASTER Act also requires periodic FDA reviews of the list, which allows it to be extended. Voluntary "may contain" warnings are a separate matter, reflecting cross-contact rather than an ingredient, and they are not governed by the same declaration rules. The European Union's list of 14 allergens, which includes celery, mustard, lupin, molluscs and sulphites, is broader. Restaurants and other food-service operators are generally outside packaged-food labeling rules, so their practices depend on local regulations and kitchen procedures.

Public health surveillance relies on several data sources. National surveys capture self-reported and clinician-diagnosed food allergy, emergency department records document severe reactions, and registries help follow patients over time. Each source has limits. Self-report can overstate or understate true allergy, and changes in diagnostic practice can make trends difficult to interpret. A Philadelphia analysis suggested that the rates of diagnosis of peanut and other IgE-mediated food allergies have declined since the adoption of guidelines encouraging early introduction practices, but such before-and-after comparisons do not establish causation.

The economic burden is substantial. A widely cited 2013 analysis based on roughly 1,600 caregivers estimated that food allergy costs $24.8 billion annually or $4184 per child. Most of that cost fell on families, with direct medical costs for food allergy ($4.3 billion) and even larger costs borne by families ($20.5 billion). Opportunity costs from caregivers leaving or changing jobs were the largest single component. Out-of-pocket costs included special foods, childcare arrangements, school changes and specialized camps. The study sample was partly recruited through an advocacy organization, which may overrepresent families who feel most affected. A 2025 societal model produced a much larger estimate, with indirect costs to society (such as productivity losses) of $343.6 billion per year, but it depends heavily on assumptions about indirect costs. Beyond money, families report anxiety about accidental exposure and constraints on social life, which are harder to quantify and are a central concern of quality-of-life research.

Research frontiers and unresolved questions

Competing explanations for the rising prevalence

The increase in prevalence of food allergy over recent decades has no single accepted explanation. The hygiene hypothesis grew out of David Strachan's 1989 observation that increasing family size was associated with a reduced risk of developing hay fever. Its application to food allergy is weak. In one family-based cohort of 1,359 children, no significant associations were identified between food allergy status and hygiene exposures including c-section birth, early infections, antibiotic use, pet ownership, childcare, and breastfeeding, although some of these exposures were linked to asthma. Pooled analyses have found a higher risk of food allergy or food atopy after caesarean delivery, but confounding by maternal age and sibling number complicates interpretation.

The dual-allergen exposure hypothesis, proposed by Gideon Lack in 2008, offers a different account. It holds that oral exposure induces an inherent immune tolerance, whereas allergic sensitization is largely caused by percutaneous exposure. Population data are consistent with this idea. Studies of peanut allergy found that its prevalence was lower in the Philippines and Israel, where peanuts are freely ingested during infancy, than in the US and UK, where early restriction had been recommended. Mouse experiments add that allergy induction through the skin can be prevented by induction of oral tolerance before skin exposure. Some researchers have since proposed the airway as a further sensitizing route, and one review notes that the hypothesis may not explain all cases of FA development. A trial of enhanced treatment for early-onset eczema is regarded as a new and convincing proof of concept that reducing skin inflammation can lower the risk of hen's egg allergy.

Vitamin D status and gut microbiota are often combined with these ideas. One integrative model suggests that allergic sensitization is promoted through cutaneous exposure, reduced diversity of the microbiota, and vitamin D deficiency. Animal work has shown that outcomes depend on host genetics as well as skin and gut microbial communities. Even so, a systematic overview of reviews found no compelling evidence that any of the interventions that had been systematically reviewed were related to the risk of food allergy. These hypotheses are not mutually exclusive, and the relative contribution of each remains unresolved.

Endotypes and biomarkers

Current tests answer the question of whether a reaction is likely better than the question of how severe it will be. Most allergists accept that the degree of IgE sensitization, whether to whole allergen or specific allergen component, is more predictive of likelihood of reaction rather than severity of reaction. Efforts to define endotypes, meaning patient subgroups defined by immune mechanism, draw on effector cells such as CD63+ basophils and on T-cell subsets with distinct cytokine profiles.

The basophil activation test is the most promising functional marker. BAT demonstrates superior discriminatory power for severe peanut and baked egg reactions, whereas Arah2 component level above 1.4 kU/L suggest a more severe peanut allergy phenotype. Component-resolved testing also helps separate low-risk pollen-related sensitization from higher-risk storage-protein sensitization. Host characteristics complicate prediction further. Recent meta-analyses refute the assumed association between asthma and more severe reactions unless asthma is poorly controlled. A history of anaphylaxis does not reliably predict future reaction severity. Validation is also difficult: there are constraints in validating the utility of a biomarker to predict the severity of allergic reactions, which may explain inconsistent findings across studies.

Ethics and regulation of new therapies

Immunotherapy is becoming available through multiple routes and doses, and biologics are increasingly used to increase the amount of food that can be safely ingested. Trials of oral immunotherapy raise distinct ethical issues. Participants, often children, receive gradually increasing doses of allergen, so informed consent from parents and assent from children must address the real possibility of severe reactions during dose escalation. Placebo-controlled designs, which are standard in randomized controlled trials, require justification when avoidance is the existing standard of care. Trials also demand emergency-capable clinical settings and careful safety monitoring.

Standardization is a second problem. Allergen extracts vary in protein content and composition between batches, which complicates comparison across studies and the regulatory approval of products. Regulators have now approved a peanut oral immunotherapy product, which carries a boxed warning about severe allergic reactions, showing that the regulatory pathway is open but narrow.

Open questions

Several questions remain unanswered. Researchers have not established why some children outgrow allergies while others do not. In peanut studies, the major determinants of persistence and the severity of peanut allergy were positive BAT and SPT outcomes, as well as sIgE and IgG4, and in egg allergy, specific antibody ratios have been associated with tolerance and persistence. Clinically, milk and egg allergies are more often outgrown, whereas peanut, tree nut, fish, and shellfish allergies tend to persist. Durable tolerance is another gap: immunotherapy can produce marked reductions in food reactivity which may be sustained for weeks or months or even longer off treatment for some patients, but the long-term stability of these effects is not yet established. Whether a cure is feasible remains uncertain. Better prediction of severity would help risk-stratify patients who might most benefit from specific immunotherapy, anti-IgE therapy, but it is not yet available. The timing and dose of early allergen introduction, and the role of microbiota and vitamin D, also remain open.

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