What is a food allergy?

A food allergy is an immunological response to a food, typically a protein, that the body mistakenly identifies as harmful. Allergic reactions are commonly associated with foods like eggs, milk, fish, peanuts, and tree nuts, though more than 120 foods have been reported as causing allergies. Symptoms can range from mild, such as itchy skin or a runny nose, to severe, including life-threatening anaphylaxis , which requires immediate medical attention. There is currently no cure for food allergies; the primary way to prevent a reaction is to avoid the offending food.

What are common symptoms of a food allergy?

Common symptoms of a food allergy can manifest in various ways, affecting different organ systems. Gastrointestinal symptoms include vomiting, pain, or diarrhea, which can occur rapidly after consuming the allergen. Oral allergy syndrome can cause itchy, swollen lips and tongue. Other symptoms include atopic dermatitis or eczema, hives, and angioedema (inflammation beneath the skin). Respiratory symptoms such as tightening of the throat, wheezing, and difficulty breathing may also occur. In severe cases, food allergies can result in life-threatening anaphylactic shock , requiring immediate medical attention.

Which foods most often cause allergies?

True food allergies are triggered by an abnormal immune response to a food component, typically a protein. While nearly any food can be an allergen, cow's milk, eggs, wheat, fish, shellfish, soybeans, peanuts, and tree nuts are the most common causes of antibody-mediated allergic reactions. Many children outgrow food allergies, but some, like those to peanuts, tree nuts, and shellfish, can be lifelong. Because there is no cure, avoidance of the causative food is the only recommended way to prevent a reaction.

How is a food allergy different from a food intolerance?

A food allergy is an immune response, often mediated by immunoglobulin E (IgE), where the body recognizes a food protein as a threat. This triggers the release of inflammatory molecules, leading to symptoms like hives, swelling, or even life-threatening anaphylaxis. Food intolerance , on the other hand, is not an immune response. It's usually a digestive issue where the body has difficulty breaking down certain foods. For example, lactose intolerance results from a deficiency in lactase, the enzyme that digests lactose in dairy products, leading to gastrointestinal discomfort.

How are food allergies diagnosed?

Food allergies are diagnosed through various methods. Immunoglobulin E (IgE) antibodies can be detected via a blood test or a skin prick test , where small amounts of allergens are scratched onto the skin to check for a reaction. An oral challenge, under medical supervision, involves eating increasing amounts of the suspected food to observe any reaction. A detailed food diary can help detect the timing and amount of food that triggers reactions, as well as the severity and duration of symptoms. An elimination diet, where a particular food is removed to see if the reaction resolves, may also identify the cause. The most conclusive test is a double-blind food challenge, though it is expensive and time-consuming.

What steps should someone take to manage a food allergy?

To manage a food allergy, strict avoidance of the problem food is critical. Read food labels carefully to identify potential allergens, and when dining out, ask about ingredients to ensure the food is safe. For accidental ingestion, medications can relieve mild symptoms; however, those with severe allergies need quick access to care to prevent life-threatening anaphylaxis. Anaphylaxis requires an epinephrine injection using an epinephrine autoinjector (like an EpiPen) to reverse the reaction’s effects by constricting blood vessels, relaxing lung muscles, and stimulating the heart. Following the injection, seek immediate medical attention.

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What is a food allergy?
A food allergy is an immunological response to a food, typically a protein, that the body mistakenly identifies as harmful. Allergic reactions are commonly associated with foods like eggs, milk, fish, peanuts, and tree nuts, though more than 120 foods have been reported as causing allergies.

Symptoms can range from mild, such as itchy skin or a runny nose, to severe, including life-threatening anaphylaxis, which requires immediate medical attention. There is currently no cure for food allergies; the primary way to prevent a reaction is to avoid the offending food.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are common symptoms of a food allergy?
Common symptoms of a food allergy can manifest in various ways, affecting different organ systems. Gastrointestinal symptoms include vomiting, pain, or diarrhea, which can occur rapidly after consuming the allergen. Oral allergy syndrome can cause itchy, swollen lips and tongue. Other symptoms include atopic dermatitis or eczema, hives, and angioedema (inflammation beneath the skin).

Respiratory symptoms such as tightening of the throat, wheezing, and difficulty breathing may also occur. In severe cases, food allergies can result in life-threatening anaphylactic shock, requiring immediate medical attention.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Which foods most often cause allergies?
True food allergies are triggered by an abnormal immune response to a food component, typically a protein. While nearly any food can be an allergen, cow's milk, eggs, wheat, fish, shellfish, soybeans, peanuts, and tree nuts are the most common causes of antibody-mediated allergic reactions.

Many children outgrow food allergies, but some, like those to peanuts, tree nuts, and shellfish, can be lifelong. Because there is no cure, avoidance of the causative food is the only recommended way to prevent a reaction.
2 Britannica Sources
1. nutritional disease: Food allergies and intolerances
2. food allergy
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How is a food allergy different from a food intolerance?
A food allergy is an immune response, often mediated by immunoglobulin E (IgE), where the body recognizes a food protein as a threat. This triggers the release of inflammatory molecules, leading to symptoms like hives, swelling, or even life-threatening anaphylaxis.

Food intolerance, on the other hand, is not an immune response. It's usually a digestive issue where the body has difficulty breaking down certain foods. For example, lactose intolerance results from a deficiency in lactase, the enzyme that digests lactose in dairy products, leading to gastrointestinal discomfort.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How are food allergies diagnosed?
Food allergies are diagnosed through various methods. Immunoglobulin E (IgE) antibodies can be detected via a blood test or a skin prick test, where small amounts of allergens are scratched onto the skin to check for a reaction. An oral challenge, under medical supervision, involves eating increasing amounts of the suspected food to observe any reaction. A detailed food diary can help detect the timing and amount of food that triggers reactions, as well as the severity and duration of symptoms. An elimination diet, where a particular food is removed to see if the reaction resolves, may also identify the cause. The most conclusive test is a double-blind food challenge, though it is expensive and time-consuming.
2 Britannica Sources
1. nutritional disease: Food allergies and intolerances
2. food allergy
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What steps should someone take to manage a food allergy?
To manage a food allergy, strict avoidance of the problem food is critical. Read food labels carefully to identify potential allergens, and when dining out, ask about ingredients to ensure the food is safe. For accidental ingestion, medications can relieve mild symptoms; however, those with severe allergies need quick access to care to prevent life-threatening anaphylaxis. Anaphylaxis requires an epinephrine injection using an epinephrine autoinjector (like an EpiPen) to reverse the reaction’s effects by constricting blood vessels, relaxing lung muscles, and stimulating the heart. Following the injection, seek immediate medical attention.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

food allergy, immunological response to a food. Although the true prevalence of food allergy is unclear, studies have indicated that about 1 to 5 percent of people have a clinically proven allergy to a food. More than 120 foods have been reported as causing food allergies, though the majority of allergic reactions in children are associated with eggs, fish, milk, peanuts, and tree nuts. There is no cure for food allergies, and avoidance of the causative food is the only recommended prevention method. Certain medications may be taken to relieve mild symptoms (e.g., itchy skin, runny nose) following unintended ingestion of the offending food. Access to care is crucial for individuals who suffer from severe food allergy; without it, the reaction can lead to life-threatening anaphylaxis (systemic allergic reaction), with inflammation of the airways, restricted breathing, and unconsciousness.

Many food allergies begin in childhood. A period of sensitization follows the first introduction of the food; during this time the child typically does not show signs or symptoms of an adverse reaction. On a later exposure to the same food, however, an allergic reaction occurs. Food allergy can develop from a combination of genetic factors and environmental exposures, as part of overall atopy, a genetic predilection toward overreactive immune responses against harmless environmental exposures. Many children outgrow their food allergies, although many of the most serious allergies, particularly those involving peanuts, tree nuts, and seafood, are lifelong.

Most symptoms of food allergy can be classified according to the organ system affected. Gastrointestinal signs can include vomiting, pain, or diarrhea and can develop rapidly after consumption of the allergen. Oral allergy syndrome (also known as pollen-food allergy) is a result of cross-sensitivity to pollen proteins and certain proteins in fruits, vegetables, and nuts. It often affects individuals with allergic rhinitis (hay fever) and manifests as itchy, swollen lips and tongue. Atopic dermatitis, or eczema, can be caused by food allergy, as can hives and angioedema, or inflammation in tissues beneath the skin. The most severe result of food allergy is anaphylaxis, to which certain persons with asthma, eczema, or hay fever may be predisposed.

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Food allergies are associated with an allergic response mediated by an antibody known as immunoglobulin E (IgE). This response usually is triggered by a protein in the food that acts as an allergen. Through sensitization to the particular allergen, the immune system develops a memory of the allergen’s molecular identity. On encountering the allergen for the first time, IgE is produced. Once IgE has been synthesized, a second exposure to the allergen induces IgE to cause the release of inflammatory molecules.

IgE antibodies can be detected through a blood test or a skin prick test. In a skin prick test, small amounts of common allergens are scratched onto the skin, usually at a series of sites on the underside of the forearm; if the person is allergic, a red, itchy wheal will develop within minutes at the prick site. To confirm a food allergy, an oral challenge may be undertaken (with medical supervision). In this test the suspected food is eaten in increasing amounts over a period of time until a reaction occurs. An oral challenge may not be possible for those who experience anaphylactic reactions.

In the case of those with milder symptoms, food allergies can be difficult to detect. The timing of a reaction can be delayed as a result of the digestive process. A detailed food diary can help in detecting the timing of reactions, as well as the amount of food that triggers them and the duration and severity of symptoms. An elimination diet, in which one particular food is eliminated in order to see if the existing reaction resolves, may be used to identify the causative food.

Because there is no prevention method for food allergies analogous to allergy shots for respiratory allergies, those with food allergies are advised to avoid their triggering food (or foods) at all costs. This can be accomplished by reading food labels, contacting the food’s manufacturer for more details about its contents, and asking about food ingredients while dining out at restaurants. In a resource-poor environment, where food labels and available emergency treatment are rare, food allergies can be especially deadly.

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Epinephrine autoinjectorThe hormone epinephrine can be administered rapidly using an epinephrine autoinjector.

The main treatment for an anaphylactic food response is injection with epinephrine or adrenaline. This can be self-administered with an epinephrine autoinjector (e.g., EpiPen), which is designed to inject a controlled amount of drug. Epinephrine constricts swollen blood vessels and decreases inflammation, providing relief from hives and tongue, throat, and airway constriction and restoring blood pressure to normal levels.

Erin Fitch

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