What Is Food Allergy? — Which Door Came First

Before the First Spoonful

When a baby is a few months old, the day comes to feed them thin porridge from a spoon for the first time. Around that time, parents gain one more worry. When can they eat eggs, is peanut okay?

The official answer to this worry has changed significantly over the past two decades or so (PMID 31690392). Guidelines in the United Kingdom, Australia, and for a time North America recommended avoiding peanuts for infants (PMID 19000582). Guidelines in the United States, Europe, and parts of Australia today have been revised toward introducing peanuts early (PMID 29588872).

What Is a Food Allergy?

The skin around a child's mouth swells and turns red within minutes of taking a bite of bread with peanut butter. Rewind this scene, and you can see what a food allergy is.

An allergy is an overreaction of the immune system to substances that are harmless to most people. A food allergy is when the immune system reacts to a protein in a certain food, causing the body to fall ill every time that food is eaten. Symptoms can appear in the skin, airways, gut, heart and blood vessels, and nervous system (PMID 30370459).

An allergen is a substance that triggers an allergic reaction, such as pollen, house dust mites, or food proteins. The protein inside a peanut is this child's allergen.

The immune system recognizes this through various cells, and eventually makes antibodies (PMID 30370459). An antibody is a Y-shaped protein produced by B cells that sticks precisely to a specific target. A B cell is a white blood cell that makes antibodies, where each cell produces antibodies that fit only one target. There are several kinds of antibodies.

One of them is the main character in food allergies. IgE is a type of antibody mainly involved in allergic reactions. The reaction comes in two stages. Sensitization is when the immune system encounters a substance for the first time and produces IgE tailored to it, with usually no symptoms during this stage.

The produced IgE attaches to the surface of mast cells. A mast cell is an immune cell stationed at the body's borders, such as the skin, airways, and gut, which waits with IgE stuck to its surface and releases substances like histamine when it encounters an allergen. That is why reactions involving IgE start quickly (PMID 30370459), usually appearing within minutes of eating (PMID 31690391).

There are also food allergies that involve the immune system but do not go through IgE. This side shows symptoms later (PMID 30370459), and gut symptoms are common in this branch of milk allergies (PMID 37851326). This article mainly deals with the fast-acting IgE side. Why the immune system reacts this way to harmless substances is explored in "What Is Allergy? — A False Alarm, and Why It Rings More Often".

Which foods are common depends on age. In infancy, milk and eggs; in childhood, peanuts and tree nuts; and in adults, fish and seafood like clams and shrimp are common (PMID 34875122). Soy and wheat are also frequently cited (PMID 31690391). One review summarizing 2021–2023 literature reported that roughly 8% of children and 10% of adults in developed countries have a food allergy (PMID 38101757). Another review notes that reliable prevalence data are lacking, and the impression that they have increased is strong (PMID 29157945).

Food allergies in children sometimes disappear as they grow. Milk and egg allergies disappear more often than peanut and tree nut allergies. However, some studies suggest that the rate of disappearance may have slowed compared to the past (PMID 26968958). Outgrowing a food allergy can happen later than expected, even during adolescence. However, peanut, tree nut, and seafood allergies often last a lifetime (PMID 31690391).

IgE-mediated food allergies are when the immune system makes IgE against food proteins and reacts within minutes upon re-exposure, and there are also non-IgE pathways that arrive later.

Why Milk Makes Your Stomach Hurt

An adult drinks a glass of milk and, an hour or two later, feels bloated and gets diarrhea. This kind of trouble is often a food intolerance. Food intolerance is trouble that happens not because the immune system is involved, but because the body cannot properly digest or process a certain food component. A prime example is lactose intolerance, which happens because the intestines lack enough of the enzyme that breaks down lactose, the sugar found in milk.

A milk allergy is an immune response to milk proteins (PMID 37851326). In lactose intolerance, the immune system does not target milk, so it does not lead to a reaction that spreads across the whole body within minutes. Even though the names sound similar, the two events work differently inside the body.

This distinction changes the dinner table. The experience of getting sick after eating is common, and that worry can lead to an overly strict diet. Often, a carefully taken medical history alone can rule out or suspect hypersensitivity to a food (PMID 34875122). A wrong diagnosis leads to unnecessary dietary restrictions, while a missed diagnosis can lead to life-threatening reactions (PMID 39710304).

Intolerance is a problem of digestion, and allergy is a response of the immune system. Which one it is changes what you need to avoid and how you need to prepare.

What a Test Can and Cannot Tell You

When you draw a child's blood to test for IgE against several foods at once, even foods the child has been eating well come back "positive" for a few. What this test result says is narrower than you might think.

There are two tests to check for IgE. A skin prick test places a drop of extract from a food on the skin and gently pricks it, seeing whether that spot swells up like a mosquito bite. A blood test measures how much IgE matching that food is in the blood. A positive result on either test shows sensitization, but that alone does not confirm an allergy diagnosis (PMID 37851326).

Diagnosing an IgE-mediated food allergy requires both a clinical history of experiencing typical symptoms after eating that food and evidence of IgE matching that food (PMID 30370459). For this reason, one review notes that only the IgE for the suspected food should be measured (PMID 34875122). The IgE level or the size of the wheal is linked to the likelihood that a reaction will occur (PMID 30370459). Whether it also tells you how severe the reaction will be is reported differently across reviews (PMID 30370459, PMID 37851326).

There is a separate test that serves as the diagnostic standard (PMID 31668274). An oral food challenge is a test where medical staff supervise as a person eats the suspected food, starting with a very small amount and increasing it step by step. The amount is raised at set intervals, and criteria for stopping if a reaction appears are established in advance. Joint guidelines from the American Academy of Allergy, Asthma & Immunology (AAAAI) and the European Academy of Allergy and Clinical Immunology (EAACI) place safety first in this test (PMID 39560049). If there are no symptoms after eating the suspected food, the allergy to that food is ruled out (PMID 30370459).

A positive result on a skin prick test or blood test is sensitization, and its size is linked to the likelihood of a reaction. Whether it is an allergy is evaluated along with the clinical history, and when it needs to be clearly determined, an oral food challenge supervised by medical staff confirms the actual reaction.

Danger That Spreads in Minutes

Most food allergy reactions do not threaten life, but deaths do occur (PMID 31690391). The most severe form has a name. Anaphylaxis is a severe allergic reaction that spreads throughout the body within minutes to hours, which can endanger life by blocking the airway or dropping blood pressure. Anaphylaxis is the most severe presentation of IgE-mediated food allergy (PMID 30370459).

The most common signs are skin symptoms like hives and swelling, and the early signs of anaphylaxis are frequently missed by both patients and clinicians (PMID 39654057). If shortness of breath or wheezing, swelling of the throat or tongue, or dizziness or fainting occurs rapidly after eating an allergen, that is an emergency requiring an ambulance and the emergency room right away. The primary treatment used for anaphylaxis is an epinephrine injection (PMID 30370459).

Factors cited behind fatal reactions include having coexisting asthma, failing to use the injection on time, having experienced a severe reaction previously, brushing off the symptoms, and being an adolescent or young adult (PMID 31690391). Asthma is covered in What Is Asthma? — An Airway That Tightens Too Easily, and the Inflammation That Keeps It Swollen.

Which reactions count as anaphylaxis is difficult to distinguish during the reaction by measuring levels of substances like histamine in the blood, and is judged by looking at the signs that appear in the body (PMID 26963947).

Shortness of breath or wheezing, swelling of the throat or tongue, and dizziness or fainting that come on rapidly after eating an allergen are emergencies that immediately require an ambulance and the emergency room.

They Told Us to Avoid It, Yet It Rose

In the United Kingdom, Australia, and North America, where guidelines advised avoiding peanuts, peanut allergies continued to grow (PMID 19000582). A trial paper published in 2015 noted that peanut allergies in children in Western countries had doubled over the preceding decade (PMID 25705822).

Early recommendations telling parents to delay giving milk, eggs, and peanuts past the first birthday to babies prone to allergies were withdrawn after newly emerged evidence showed that the approach failed to prevent food allergies (PMID 31261990).

Around that time, a study comparing two countries was published. Upon surveying 5,171 Jewish schoolchildren in the UK and 5,615 in Israel, the prevalence of peanut allergy was 1.85% in the UK and 0.17% in Israel. Even after accounting for differences in allergic predisposition, the risk on the UK side was 9.8-fold higher (PMID 19000582).

The babies in the two countries ate differently. Israeli babies ate peanuts earlier, more often, and in larger amounts, whereas British babies generally did not eat peanuts. The authors concluded that this difference could not be explained by allergic constitution, social class, genetic background, or differences in the peanuts themselves (PMID 19000582).

This study is an observational study conducted via questionnaire. An observational study is research that does not interfere with people's lives, leaves them to live as they normally do, and watches what happens afterward. The eating habits of the babies were examined separately in 77 and 99 infants. Observational studies show things happening together, but it is hard to tell what causes what. Because of this, the authors also ended their conclusion with the question, "Can early feeding prevent peanut allergy?" (PMID 19000582).

Under the recommendation to avoid it, peanut allergies increased, and they were roughly ten times lower in Israeli Jewish children who ate them early and often. What this comparison left behind was a question to be tested.

A Test Decided by a Draw, LEAP

That question was tested by a trial called LEAP. A randomized controlled trial is a test where participants are divided randomly like a draw, one side is given a certain treatment, and the results are compared with the other side. When divided by a draw, the two groups become similar to each other except for the treatment, so the difference in results can be read as the effect of the treatment.

LEAP selected only babies who were prone to allergies. Atopic dermatitis is a skin disease where the skin is dry, extremely itchy, and inflammation repeats for a long time, often also called eczema. High-risk infants are babies who are judged to have a high likelihood of developing a certain allergy. In peanut allergy, babies with egg allergy, severe eczema, or both are considered high-risk infants (PMID 31690392).

The trial enrolled 640 high-risk infants between 4 and 11 months of age. Before entering, the babies received a skin prick test and were divided into only two groups: a group with no swelling and a group with 1 to 4 mm of swelling. Babies who swelled larger than that, already reacting strongly, were not in this trial. Then, each group was divided by a draw, and until age 5, one side consistently ate peanuts while the other side avoided them (PMID 25705822).

The results were measured at age 5. Among the 530 people who had no swelling at the initial test, 13.7% of the group that avoided peanuts and 1.9% of the group that ate them had a peanut allergy. Among the 98 people who had slight swelling from the beginning, 35.3% of the avoidance group and 10.6% of the eating group had it. There was no difference between the two sides in serious adverse events (PMID 25705822).

The effect lasted long. Even when the children who had been eating peanuts stopped eating them for one year after age 5, peanut allergy did not significantly increase, and at age 6 it was 18.6% for the avoidance side and 4.8% for the eating side (PMID 26942922). When 508 of the original participants were re-examined at age 12, even though there had been a period in between where both sides did not eat peanuts for a long time, it was 15.4% for the avoidance side and 4.4% for the eating side (PMID 38804779).

The effect stayed only with peanuts. Babies who ate peanuts also did not avoid sensitization to other foods or things like pollen, other allergic diseases, reactions to tree nuts and sesame, nor did their eczema heal any faster (PMID 29097103).

When babies with severe eczema or egg allergy were selected through a test and babies already reacting strongly were excluded, the group that ate peanuts early and consistently had far fewer peanut allergies, and that difference lasted into adolescence. It did not prevent other allergies.

Does It Apply to All Babies, Too?

The babies in LEAP were high-risk infants. Around the same time, there was a trial in the UK called EAT involving general population infants. A total of 1,303 exclusively breastfed 3-month-old infants were divided into an early-introduction group—starting six foods early: peanut, cooked egg, milk, sesame, whitefish, and wheat—and a standard-introduction group following the UK recommendation at the time to breastfeed exclusively until around 6 months of age (PMID 26943128).

When comparing the groups strictly as originally allocated, infants who developed an allergy to one or more of the six foods were 7.1% in the standard-introduction group and 5.6% in the early-introduction group, showing no confirmed difference. Looking separately only at the babies who ate as planned, it was 2.4% versus 7.3%, with fewer in the early-introduction group. Feeding all six foods early was difficult to achieve, but it was safe (PMID 26943128). Analyses looking only at babies who followed the plan can be biased (PMID 36435990).

A later pooled analysis combining the data of the babies from both trials reported that, even when compared strictly by the groups as originally allocated, peanut allergy was 75% lower in the early-introduction group. The reduction was seen across all risk groups, including children without eczema, and the earlier the introduction, the greater the effect (PMID 36435990).

The evidence for other foods is less solid. A pooled analysis of trials conducted for EAACI guidelines concluded that introducing well-cooked egg early likely reduces egg allergy, but pasteurized-only raw eggs do not. It also noted that conclusions regarding peanuts are of moderate certainty, derived from single trials in high-income countries where peanut allergy is common (PMID 32396244). The effect of early milk introduction is not yet settled, and in Japan—where people eat fewer peanuts and peanut allergies are also rare—the effect of early peanut introduction appears smaller (PMID 41187903).

The evidence for peanuts is most solid in high-risk infants. In general population infants, the original analysis of EAT did not confirm a difference, but a subsequent pooled analysis of the two trials reported a reduction across all risk groups, including children without eczema. The evidence is uneven for other foods and in countries where peanuts are eaten less frequently.

Which Door Did It Meet First?

The homes of 133 children with peanut allergies consumed 18.8g of peanuts per week per household, which was more than the homes of children without allergies (6.9g). However, the amount of peanuts eaten by the babies themselves did not differ between the groups (PMID 19203660).

The authors of this questionnaire-based study concluded that encountering peanuts frequently in the environment during infancy rather than through the mouth appears to promote sensitization, and that encountering them in small amounts might actually be protective for a child with an allergic predisposition. They also noted that even for such babies, early oral ingestion may have acted protectively (PMID 19203660).

This scene leads to the idea that there are two doors through which peanuts enter the body. Oral tolerance is a state in which the immune system does not react to food that enters the body through the mouth and reaches the gut. This tolerance is the original response to food that enters through the mouth (PMID 29307410). The principles by which immunity is maintained so that it does not attack our own bodies or harmless substances are followed in "Why Doesn't the Immune System Attack Us? — The Brakes on the Patrol".

The dual-allergen exposure hypothesis is that if food is encountered first through damaged skin, sensitization is likely to occur, whereas if it is eaten steadily through the mouth first, tolerance is likely to develop. Evidence that encountering it early through the mouth via an intact gut usually leads to tolerance, while encountering it through damaged skin or airways commonly leads to sensitization, has refined this hypothesis (PMID 39924626). Evidence is also accumulating that when allergens enter through the surfaces of damaged skin and the gut, allergy-type inflammation is turned on (PMID 38360544).

The fact that eczema is the strongest risk factor in infancy aligns with this hypothesis (PMID 41187903). Eczema itself is not an allergic reaction, but people with eczema have a higher rate of sensitization to things like food and pollen than the general population (PMID 39924626). The question of whether simply blocking the skin door works still has weak answers. A 2026 review paper noted that moisturizers alone are not enough to prevent food allergies, and that actively managing the inflammation of eczema may be important (PMID 41187903).

This analogy has limitations. In reality, the responses of multiple cells accumulate to determine the outcome, and there are no gatekeepers standing at each door making judgments. Food allergies do develop even in children without risk factors like eczema (PMID 33250376).

It is a leading hypothesis that the same peanut is likely to lead to sensitization if met first through damaged skin, but to tolerance if met steadily first through the mouth. However, it is still a hypothesis.

A Five-Month-Old Baby with Severe Eczema

We apply what we saw earlier to an infant. There is a five-month-old baby with severe eczema on the face and arms.

This infant falls into the high-risk infant group (PMID 31690392). In LEAP, infants like this first received a skin prick test, and infants who swelled up significantly did not enter the trial (PMID 25705822).

Suppose a peanut IgE blood test comes back positive for this baby. That result alone does not confirm an allergy, but the IgE level connects to the likelihood that a reaction will occur (PMID 30370459). In LEAP as well, within the group that swelled 1 to 4 mm, 35.3% of those who avoided peanuts developed a peanut allergy, and larger swelling was associated with peanut allergy (PMID 25705822).

The flip side of the fact also applies to this baby. The practice of delaying past the first birthday was withdrawn as evidence emerged that it has no effect in preventing food allergies (PMID 31261990). U.S. guidelines branch based on the degree of risk, separately prescribing how to use tests for high-risk infants and whether the setting for first feeding peanuts should be a medical institution or at home (PMID 28065802).

The benefits of LEAP came from high-risk infants who entered through testing, and the practice of delaying past the first birthday was withdrawn based on evidence of no effect. Guidelines differ on when and how to evaluate high-risk infants and begin.

How the Guidelines Changed

Once LEAP came out, allergy prevention guidelines in many countries changed quickly, recommending that peanut be introduced early (PMID 35394609). In 2017, the U.S. National Institute of Allergy and Infectious Diseases (NIAID), together with 25 organizations, issued supplementary guidelines for preventing peanut allergy. These guidelines are divided into three paths for babies with different levels of risk (PMID 28065802).

Some parts of the guidelines differ from one another. In 2021, three American and Canadian societies, including the AAAAI, recommended introducing peanut and egg around 6 months of age and not earlier than 4 months, and noted that testing before introduction is not strictly necessary but that some families want it (PMID 33250376). This is a different tone from the 2017 U.S. guidelines, which divided paths by risk level. Such differences between guidelines highlight issues like whether families can accept them, cost, and feasibility (PMID 34311123).

There are also points where the guidelines point in the same direction. Pregnant or breastfeeding people are not advised to cut out specific foods to prevent allergies in their babies (PMID 33250376, PMID 37389093).

People also began looking at whether peanut allergies actually decreased after the guidelines changed. Looking at electronic health records from pediatric primary care networks across several U.S. states, the cumulative rate of peanut allergy diagnoses in children aged 0 to 3 fell from 0.79% before the guidelines to 0.45% after the supplementary guidelines (PMID 41110838). The authors viewed this result as supporting the intended effect of the guidelines. Because this is an observational study comparing periods within a single country's care network, it shows an association that they decreased alongside the guidelines.

Guidelines shifted from delaying peanut to introducing it early. However, details such as who should be tested first are written differently across guidelines.

Once an Allergy Has Developed

The story of prevention is for babies who do not yet have an allergy. For a person in whom a food allergy has already been confirmed, what the 2025 EAACI guidelines point to as the basics are dietary guidance to avoid that food, education on recognizing reactions, a written treatment plan, and having emergency medication on hand (PMID 39473345).

In addition to this, there is an area of treatment performed by specialized institutions where research continues: Oral immunotherapy is a treatment that aims to raise the reaction threshold by having a person who already has a food allergy eat that food, starting from a very small amount and increasing it according to a set schedule. The same EAACI guidelines recommend this treatment for children and adolescents with a peanut allergy (PMID 39473345).

This treatment comes with a price. In an analysis combining 12 peanut oral immunotherapy trials, this treatment increased the amount one could eat and tolerate, but it raised the risk of anaphylaxis by about 3-fold compared to the side that only avoided the food or used a placebo (high certainty), and no difference in quality of life was confirmed (low certainty). The authors concluded that safer treatment methods are needed (PMID 31030987). A more recent pooled analysis also noted that while effects during treatment were seen, the evidence for long-lasting tolerance is not of high quality (PMID 38747333).

For an allergy that has already developed, avoidance and emergency preparedness are the basics, and oral immunotherapy is a treatment and research endeavor by specialized institutions that weighs benefits and risks together.

Where to Look Next

Whether introducing peanuts earlier works to the same magnitude in foods other than peanuts, in low-risk infants, and in countries where peanuts are eaten less is still being studied (PMID 32396244, PMID 41187903).

Why trials like LEAP carry more weight than observational studies, and where their limits arise, can be found in "Is the Randomized Controlled Trial Really the 'Gold Standard'?". Why a positive blood test is not necessarily an allergy continues in "What a Test Actually Tells You — An Introduction to Sensitivity, Specificity, and Pretest Probability".

The immune system reacting to harmless pollen or house dust mites is followed up by "What Is Allergy? — A False Alarm, and Why It Rings More Often". The principle by which immunity decides what not to attack can be seen in "Why Doesn't the Immune System Attack Us? — The Brakes on the Patrol". How antibodies come to have so many shapes is covered by "What Is an Antibody? — Millions of Keys Cut in Advance, and the Ones That Fit".

Source Papers

• "Food allergy prevention: Where are we in 2023?" (2023) — PMID 37389093 — Recommends against avoiding allergens during pregnancy and lactation, no confirmed link between breast milk and reduced food allergies, and early, active, and continuous introduction of peanuts and eggs upon starting solids.
• "Prevention of food allergy." (2019) — PMID 31690392 — Infant feeding recommendations have changed dramatically over the past 20 years, egg allergy, severe atopic dermatitis, or both = high risk for peanut allergy, rationale for early peanut introduction, no rationale for additional changes to mother and baby diets or mother elimination diets.
• "Early consumption of peanuts in infancy is associated with a low prevalence of peanut allergy." (2008) — PMID 19000582 — Increase in peanut allergies despite avoidance guidelines in the UK, Australia, and (for a time) North America, Jewish students 1.85% in the UK of 5,171 vs 0.17% in Israel of 5,615, adjusted hazard ratio 9.8, Israeli babies ingest earlier, more frequently, and in larger amounts, not explained by differences in atopy, social class, genetics, or peanuts, the conclusion questions whether early introduction prevents it.
• "Preventing Peanut Allergy." (2018) — PMID 29588872 — Early introduction is a paradigm shift from previous recommendations, US, European, and Australasian guidelines updated, interest in the role of the skin barrier, peanut allergies are difficult to outgrow.
• "IgE-Mediated Food Allergy." (2019) — PMID 30370459 — Immune response to food proteins, mast cell and basophil IgE binding → release of histamine, etc., rapid onset, non-IgE has delayed onset, diagnosis = typical history + specific IgE, levels and wheal size do not predict severity but relate to probability, exclude if eaten without symptoms, anaphylaxis is the most severe form, injectable epinephrine is the primary treatment.
• "Food allergy: Diagnosis and treatment." (2019) — PMID 31690391 — IgE reactions usually occur within minutes, mostly non-fatal but deaths occur, risk factors for fatal anaphylaxis (asthma, delayed injection, history of severe reactions, denial of symptoms, adolescents, young adults), common foods, natural tolerance even in adolescence, peanuts, tree nuts, and seafood are often lifelong.
• "Cow's Milk Protein Allergy." (2024) — PMID 37851326 — Immune response to milk proteins, IgE, non-IgE, and mixed, intestinal symptoms common in non-IgE, gold standard = double-blind placebo-controlled oral food challenge, specific IgE and skin prick tests only show sensitization and do not contribute to definitive diagnosis.
• "Food allergy and hypersensitivity reactions in children and adults-A review." (2022) — PMID 34875122 — Adverse food reactions commonly reported and anxiety leads to strict diets, can be excluded or suspected with a careful medical history, analyze only IgE for suspected allergens, milk and eggs in infants, peanuts and tree nuts in children, fish and shellfish in adults.
• "Feast for thought: A comprehensive review of food allergy 2021-2023." (2024) — PMID 38101757 — About 8% of children and 10% of adults in developed countries, early introduction appears to be the most effective preventive intervention.
• "Food allergy: A review and update on epidemiology, pathogenesis, diagnosis, prevention, and management." (2018) — PMID 29157945 — Reliable prevalence data lacking, strong impression of an increase.
• "The Natural History of Food Allergy." (2016) — PMID 26968958 — Milk and eggs are more likely to be outgrown than peanuts and tree nuts, the rate of outgrowing may have slowed.
• "Novel diagnostics in food allergy." (2025) — PMID 39710304 — Misdiagnosis leads to unnecessary diets and social restrictions, failure to diagnose threatens life through anaphylaxis.
• "Food Allergy Testing." (2019) — PMID 31668274 — The gold standard for diagnosing IgE food allergy is the oral food challenge, specific IgE and skin prick tests are auxiliary.
• "AAAAI-EAACI PRACTALL: Standardizing oral food challenges-2024 Update." (2024) — PMID 39560049 — Safety of the challenge is paramount, protein-based half-log dose increases at 20 to 30 minute intervals, stopping criteria.
• "Anaphylaxis." (2024) — PMID 39654057 — Most common signs are skin symptoms such as hives and angioedema, both patients and clinicians often miss early signs.
• "Anaphylaxis in children." (2016) — PMID 26963947 — Histamine and tryptase are not accurate enough for routine diagnosis, relying instead on clinical signs.
• "Randomized trial of peanut consumption in infants at risk for peanut allergy." (2015) — PMID 25705822 — Western children's peanut allergy doubled over 10 years, 640 infants aged 4 to 11 months with severe eczema, egg allergy, or both, two cohorts with no skin prick test wheal / 1 to 4 mm, peanut allergy at 60 months negative cohort 13.7% vs 1.9% · positive cohort 35.3% vs 10.6%, no difference in serious adverse events, larger skin prick test wheals associated with peanut allergy, increased IgG4 and elevated IgE in the consumption group versus avoidance group.
• "Prevention of Food Allergy: The Significance of Early Introduction." (2019) — PMID 31261990 — Recommendations to delay milk, eggs, and peanuts past the first birthday in high-risk infants withdrawn as new evidence showed no effect, guidelines for early introduction.
• "Effect of Avoidance on Peanut Allergy after Early Peanut Consumption." (2016) — PMID 26942922 — LEAP-On: even after 12 months of avoidance, 72 months 18.6% vs 4.8%, no increase in prevalence in the consumption group, long-term effects unknown.
• "Follow-up to Adolescence after Early Peanut Introduction for Allergy Prevention." (2024) — PMID 38804779 — 508 of 640 participants, 144 months 15.4% vs 4.4%, long-term avoidance periods in both groups, tolerance persisting into adolescence.
• "Allergen specificity of early peanut consumption and effect on development of allergic disease in the Learning Early About Peanut Allergy study cohort." (2018) — PMID 29097103 — Effect is peanut-specific, does not prevent other allergic diseases, other sensitizations, tree nut, or sesame reactions, and does not accelerate the resolution of eczema or egg allergy.
• "Randomized Trial of Introduction of Allergenic Foods in Breast-Fed Infants." (2016) — PMID 26943128 — EAT: 1,303 breastfed 3-month-old infants from the general population, early introduction of six foods vs breast milk alone until around 6 months, ITT 7.1% vs 5.6% (P=0.32) efficacy not proven, per-protocol analysis 2.4% vs 7.3%, early introduction was not easy but safe.
• "Early introduction of peanut reduces peanut allergy across risk groups in pooled and causal inference analyses." (2023) — PMID 36435990 — Combined individual data from LEAP and EAT, 75% reduction in ITT, protective effect across all risk groups including children without eczema, earlier introduction yielded greater effects, per-protocol analysis can be biased.
• "Preventing food allergy in infancy and childhood: Systematic review of randomised controlled trials." (2020) — PMID 32396244 — Systematic review for EAACI, avoidance, vitamins, fish oil, pro- and prebiotics, and moisturizers may have little effect (very uncertain), well-cooked eggs likely reduce egg allergy (not pasteurized raw eggs), peanuts likely result in a large reduction in high-risk infants in countries with high prevalence — moderate certainty from single trials in high-income countries, validation needed in broader populations.
• "Preventing Food Allergy by Early Food Introduction: East Meets West With the Lack Dual-Allergen Exposure Theory." (2026) — PMID 41187903 — Eczema is the strongest early risk factor, early milk introduction conclusion undecided, appears less effective in Japan where peanut consumption and prevalence are low, moisturizers alone are insufficient, aggressive anti-inflammatory treatment may be important.
• "Household peanut consumption as a risk factor for the development of peanut allergy." (2009) — PMID 19203660 — Weekly peanut consumption in 133 households of children with peanut allergy 18.8g vs 6.9g in non-allergic controls and 1.9g in high-risk controls, no difference in infant ingestion, high environmental (non-oral) exposure appears to promote sensitization.
• "Mechanisms of food allergy." (2018) — PMID 29307410 — Oral tolerance is a normal physiological response to ingested antigens, this process appears to have broken down over the past 20 years.
• "Allergens in Atopic Dermatitis." (2025) — PMID 39924626 — Atopic dermatitis is not an allergic reaction in itself, but has a high rate of sensitization to food and inhalant allergens, dual-allergen exposure hypothesis: early oral exposure through an intact gut usually induces tolerance, exposure through damaged skin and respiratory tracts often causes sensitization.
• "The Immunobiology and Treatment of Food Allergy." (2024) — PMID 38360544 — Growing evidence that allergen exposure through damaged skin and gut epithelia activates allergic inflammation.
• "A Consensus Approach to the Primary Prevention of Food Allergy Through Nutrition" (2021) — PMID 33250376 — AAAAI, ACAAI, CSACI: eczema is the highest risk factor but children without risk factors also develop food allergies, introduce peanuts and eggs around 6 months, not before 4 months, screening tests before introduction unnecessary but available to families who want them, recommends against avoiding allergens during pregnancy and lactation.
• "Real-World LEAP Implementation." (2021) — PMID 35394609 — International guidelines quickly changed to recommend early introduction following LEAP.
• "Addendum guidelines for the prevention of peanut allergy in the United States" (2017) — PMID 28065802 — NIAID-led with 25 organizations, three guidelines by risk level, use of tests (specific IgE, skin prick, oral challenge) and timing and methods of introduction at medical facilities or home.
• "International Peanut Allergy Prevention, 6 Years After the Learning Early About Peanut Study." (2022) — PMID 34311123 — Differences between guidelines reveal implementation challenges such as acceptability, cost, adherence, and feasibility.
• "Guidelines for Early Food Introduction and Patterns of Food Allergy." (2025) — PMID 41110838 — Electronic health records from a pediatric primary care network in multiple US states, cumulative incidence of peanut IgE food allergy in ages 0 to 3 dropped from 0.79% to 0.45% (following addendum guidelines), reduction following guidelines.
• "EAACI guidelines on the management of IgE-mediated food allergy." (2025) — PMID 39473345 — Avoidance after diagnosis, dietary advice, written treatment plan, symptom recognition education, and auto-injector prescription are essential, recommends oral immunotherapy for children and adolescents with peanut allergy.
• "Oral immunotherapy for peanut allergy (PACE): a systematic review and meta-analysis of efficacy and safety." (2019) — PMID 31030987 — 1,041 participants across 12 trials, oral immunotherapy increases anaphylaxis risk RR 3.12 compared to avoidance or placebo despite desensitization (high certainty), no difference in quality of life (low certainty).
• "Immunotherapy and biologics in the management of IgE-mediated food allergy: Systematic review and meta-analyses of efficacy and safety." (2024) — PMID 38747333 — Desensitization during treatment is effective, but evidence for long-term tolerance is of low quality.