What are food allergies?

Food allergies are an unpleasant and sometimes dangerous reaction of the body’s immune system to even minute amounts of certain foods that contain protein allergens. Allergy to food carbohydrates also occurs in the alpha-gal syndrome. Some children may be extremely sensitive and react to trace amounts of food allergens, whereas others may tolerate higher amounts of a food allergen before experiencing symptoms.

What causes food allergies?

The development of food allergy begins with sensitization, when a susceptible individual develops food-specific IgE antibodies after a food-protein antigen contacts the gut, respiratory tract, or skin. It is unclear why some become food-allergen sensitized and develop clinical allergies while others do not. However, infants with eczema have a high risk for developing food allergies. There also appears to be a genetic component to susceptibility to food allergy, they can run in families. Food allergies may also be associated with the timing of introduction of foods to babies, overuse of antibiotics, living in urban areas, or living in industrialized countries.

The likelihood of developing food-induced allergic symptoms can be increased by a variety of conditions including concurrent illness, fever, exercise, alcohol consumption, menstruation, and aspirin and other nonsteroidal anti-inflammatory drugs. And biphasic reactions can occur hours after the initial reaction. Of particular concern is food-dependent exercise-induced anaphylaxis, triggered by exercise within 4 to 6 hours after eating the food allergen.

In the U.S. an estimated 8% of children and 11% of adults have food-protein allergies. Sensitization to alpha-gal ranges from 20% to 31% in the southeastern U.S.–an estimated 96,000 to 450,000 individuals.

In the U.S. 9 foods account for more than 90% of food allergies—shellfish, dairy, peanut, tree nuts, fin fish, egg, wheat, soy, and sesame. Peanut is the leading cause of death from anaphylaxis in the U.S. followed by tree nuts and shellfish. The alpha-gal syndrome is an allergy to red meat, an immune reaction that develops after being bitten by a tick.

What are the symptoms of food allergies?

Symptoms usually occur almost immediately within minutes but sometimes up to 1-2 hours after eating the food a person is sensitive to. Common symptoms include hives, itching, nasal congestion, flushed skin, lip or tongue swelling, throat tightening, shortness of breath, crampy abdominal pain, vomiting, and/or diarrhea. Rather than causing immediate symptoms, the alpha-gal syndrome usually presents as a delayed reaction about 2 to 6 hours after eating red meat.

Mild allergic symptoms including itching, mild gastrointestinal upset, or small areas of isolated hives and swelling can be decreased by treatment withan oral antihistamine such as cetirizine or diphenhydramine.

The most severe allergic reaction is anaphylaxis, which can cause airway constriction, wheezing, shortness of breath, low blood pressure, palpitations, dizziness or fainting, nausea, vomiting, diarrhea, and death if not promptly treated with self-injected or health care provider injected intramuscular epinephrine, which may be repeated every 5 minutes if allergic symptoms persist.

People experiencing food related anaphylaxis should seek emergency care, where they may receive additional doses of epinephrine, antihistamines, corticosteroids, and inhalers. Fatality due to food related anaphylaxis in the U.S. is rare at 4 deaths per 100 million per year.

How is food allergy diagnosed?

The usual way people who have had a reaction to food are evaluated is with a blood test or skin prick test performed by an allergist to detect the presence of food-specific immunoglobulin E (IgE) antibodies. The alpha-gal syndrome is diagnosed by the detection of alpha-gal IgE antibodies in persons with an allergic reaction after eating mammalian meat products.

Allergists may also perform an oral challenge test, in which an individual eats a specific food of concern, and a subsequent allergic reaction confirms a food allergy diagnosis. Oral challenge testing may cause a severe allergic reaction, so it should only be done under close medical supervision.

How can food allergy be managed?

Among those who have a IgE-food allergy the principal approach to its management is avoidance of the causal food allergen. This may require a high level of vigilance on the part of both parents and children to keep the dangerous foods out of the household, schools, and elsewhere where they may be encountered in daily life–especially among those children who have been found to be highly susceptible by reacting with anaphylaxis.

To avoid the food that triggers an allergic reaction, individuals should read packaged food ingredient labels and call manufacturers directly to address questions about food handling and cross contamination. They are required by U.S. federal law to list any of the 9 most common foods that cause allergic reactions. People should also disclose their food allergies and exercise caution when eating out at restaurants or elsewhere.

An individual with alpha-gal syndrome should completely stop eating mammalian meat such as beef, pork, or lamb. Some individuals may also need to stop eating mammalian-based products such as cow’s milk, cheese, or gelatin. Symptoms can be avoided in most individuals who follow this food avoidance strategy. If additional tick bites are avoided the alpha-gel syndrome often fades with time, so prevention is facilitated by to avoiding future tick bites.

Certain medications, such as a blood thinner (heparin), snake antivenom, and certain cancer medications (such as cetuximab), as well as mammal-based organ replacements (such as heart valves) can cause allergic reactions in patients with alpha-gal syndrome and should be avoided.

All individuals with a food allergy should know how to identify and treat mild, moderate, and severe allergic reactions. They should always have access to an epinephrine auto-injector device (EpiPens and Auvi-Q) or epinephrine nasal spray (Neffy) and other medications such as antihistamines and inhalers to treat food related allergic reactions and anaphylaxis.

Can food allergies be cured?

Some individuals with food allergies may undergo oral immunotherapy, also called food allergy desensitization. Administered by an allergist, oral immune therapy involves consumption of small, successively increasing amounts of a food allergen, or multiple allergens, and then maintenance of a daily target amount indefinitely. This is not a therapy that any parent should try on their own. Currently, only oral immunotherapy for peanut allergy has received U.S. Food and Drug Administration approval. In addition, many children’s response to some allergens such as to egg and milk diminish or disappear over time–but fewer than one-third of children outgrow peanut or tree nut allergies.

Not everyone outgrows egg and dairy.  There is a baked egg and baked dairy study that shows children building tolerance-but not everyone. Xolair (omalizumab) is being used to reduce allergic responses.  Allergic individuals still need to avoid all allergens but Xolair seems to reduce the allergic reaction.

Can food allergies be prevented?

A prominent approach to the prevention of food allergies among children is focused on the timing of the introduction of the various foods that commonly cause food allergies. For years it was thought that pregnant and nursing mothers should avoid eating peanuts and other common allergens and delay the introduction of certain foods until an infant was 3 years old. This advice was abandoned when it was not found to be very effective and subsequent studies found that peanut allergy was lower among the infants of women who ate peanuts during pregnancy.

An important influence on changing the advice about when to introduce foods was a 2015 clinical trial in UK infants. It found that earlier peanut introduction brought about an 86% relative risk reduction in peanut allergy development if peanut-containing foods were introduced between 4 and 11 months of age. However, the infants studied were at high-risk of developing allergies because they had early-onset eczema, and the study may not be as relevant to a general population.

The UK study led to changes in infant feeding guidelines in many countries. For example, in 2016 Australian guidelines recommended early introduction of peanut foods before age 12 months for all infants to reduce the risk of peanut allergy. To evaluate the impact of the changed guidelines, a 10-year study was undertaken to measure any change in the prevalence of peanut allergy among Australian infants.

The study did find that when peanut introduction at age 12 months was compared to introduction at age 6 months or younger there was a significantly lower risk of peanut allergy among infants of Australian ancestry but no significant decline among infants of East Asian ancestry–an ethnic group considered to be more susceptible to developing food allergies.

The study found that after standardizing for infant ancestry and other demographics changes, over the 10-year period, peanut allergy prevalence in the general population of infants was not significantly decreased by the new guidelines. It remained at 2.6% in 2018-2019, compared with 3.1% in 2007-2011.

Another study found that the use of cow’s milk formula earlier than 3 days after birth to supplement breastfeeding more than doubled the likelihood of sensitization to cow’s milk and increased the frequency of other food allergies. The study authors noted that there is no clear clinical evidence to support the early introduction of cow’s milk formula and recommend avoiding it for the first 3 day after childbirth to prevent the development of food allergies.

A 2023 systematic review and meta-analysis, considered 23 randomized clinical trials that evaluated age at allergenic food introduction (milk, egg, fish, shellfish, tree nuts, wheat, peanuts, and soya) during infancy and the development of immunoglobulin E (IgE)–mediated food allergy from 1 to 5 years of age.

The study authors found that there was high-certainty evidence that introduction of egg, from 3 to 6 months of age, was associated with reduced risk of egg allergy, and high-certainty evidence that introduction of peanut from 3 to 10 months of age was associated with reduced risk of peanut allergy. Evidence for timing of introduction of cow’s milk and risk of cow’s milk allergy was considered to be of very low certainty.

The study concluded that earlier introduction of multiple allergenic foods in the first year of life was associated with lower risk of developing food allergy. The authors noted that uncertainty was introduced into studies they evaluated because there was a high rate of withdrawal from the feeding interventions for a variety of reasons including feeding difficulties and parent-reported allergy symptoms. They concluded that further work is needed to develop more acceptable forms of multiple allergenic food interventions that are safe and acceptable for infants and their families.

Introduction of complementary foods (i.e., solid foods introduced to infants between the ages of 4 and 6 months to complement breastfeeding and/or formula feeds) is a fundamental topic of discussion every pediatrician should have with families of young infants.

This brings up an issue on which there is conflicting advice. Should single ingredient foods should be introduced one at a time with a gap prior to feeding a different food? The American Academy of Pediatrics (AAP) recommends introduction of solid foods between the ages of 4 and 6 months. The AAP and the Centers for Disease Control and Prevention (CDC) further recommend introducing one single-ingredient food at a time and observing the infant for 3 to 5 days between the introduction of each new food to monitor for allergic reactions.

A recent survey notes, “Although it is important to monitor for adverse food reactions in infants, it is unclear why specifically a 3- to 5-day period is recommended.” It goes on to say that since early introduction of complementary foods is beneficial, the current published feeding recommendations may hinder the rapid introduction of a diverse diet and negatively affect the timely coordination of early peanut introduction in infants.
.
The survey found that most pediatric practitioners did not counsel families to wait 3 days or longer, some recommended 2 days, others 1 day and still others did not recommend a gap between types of food unless infants were considered at risk for food allergy development.
And most practitioners recommended waiting 2 days or less between the introduction of new foods, with only 2 of 5 reported following the AAP and CDC recommendation of waiting 3 to 5 days between the introduction of new foods. Most also believed that administering multiple nonallergenic foods was safe, although only 2.7% recommended it. Despite reporting that food-related reactions occurred infrequently among infants, most practitioners recommended waiting longer and complying with AAP recommendations for infants with food allergy risk factors, with 66.3% recommending 3 or more days between the introduction of new foods.

The survey authors concluded: “Because the approach to food allergy prevention has changed, a reevaluation of published feeding guidelines may be necessary. Further research appears to be needed to explore an introduction schedule that is evidenced based, safe, and practical for infants and their families.”

Conclusion

The general information in this report is not a substitute for expert medical diagnosis and care. Both parents and children with a food allergy should rely on the advice of their pediatricians and/or allergists for guidance about their own situation. They should know how to be vigilant to avoid foods that trigger allergic reactions and be able to identify and treat mild, moderate, and severe allergic reactions. They should always have access to an epinephrine auto-injector device (EpiPens and Auvi-Q) or epinephrine nasal spray (Neffy) and other medications such as antihistamines and inhalers to treat food related allergic reactions and anaphylaxis.

References:
Information and language text for this report has been taken from the following publications:

Du Toit G, Roberts G, Sayre PH, et al; LEAP Study Team. Randomized trial of peanut consumption in infants at risk for peanut allergy. N Engl J Med. 2015;372(9):803-813. doi:10.1056/NEJMoa1414850

Urashima M, Mezawa H, Okuyama M, et al. Primary Prevention of Cow’s Milk Sensitization and Food Allergy by Avoiding Supplementation With Cow’s Milk Formula at Birth: A Randomized Clinical Trial. JAMA Pediatr. 2019;173(12):1137–1145. doi:10.1001/jamapediatrics.2019.3544

Samady W, Campbell E, Aktas ON, et al. Recommendations on Complementary Food Introduction Among Pediatric Practitioners. JAMA Netw Open. 2020;3(8):e2013070. doi:10.1001/jamanetworkopen.2020.13070

Dantzer J, Wood RA. Can Peanut Allergy Prevention Be Translated to the Pediatric Population? JAMA. 2022;328(1):25–26. doi:10.1001/jama.2022.6263

Scarpone R, Kimkool P, Ierodiakonou D, et al. Timing of Allergenic Food Introduction and Risk of Immunoglobulin E–Mediated Food Allergy: A Systematic Review and Meta-analysis. JAMA Pediatr. 2023;177(5):489–497. doi:10.1001/jamapediatrics.2023.0142

Soriano VX, Peters RL, Moreno-Betancur M, et al. Association Between Earlier Introduction of Peanut and Prevalence of Peanut Allergy in Infants in Australia. JAMA. 2022;328(1):48–56. doi:10.1001/jama.2022.9224

Iglesia EGA, Kwan M, Virkud YV, Iweala OI. Management of Food Allergies and Food-Related Anaphylaxis. JAMA. 2024;331(6):510–521. doi:10.1001/jama.2023.26857

Voelker R. What Are Food Allergies? JAMA. 2024;332(5):434. doi:10.1001/jama.2024.6703

Mollah F, Zacharek MA, Benjamin MR. What Is Alpha-Gal Syndrome? JAMA. 2024;331(1):86. doi:10.1001/jama.2023.23097

Back to top