Food allergy

Related Terms

Allergen, allergens, allergic, allergic reaction, allergic asthma, response, allergies, allergy, anaphylaxis, antibodies, antibody, asthma, epinephrine, epinephrine auto-injector, food additives, food intolerance, food poisoning, hypersensitivity, (IgE), immune, immune defense system, immune response, immune system, immunoglobulin, immunoglobulin E, lactose intolerance, radioallergosorbent test (RAST?), sensitization, sensitized, white blood cells.

Background

A food allergy occurs when an individual's immune system mistakes a food protein for a foreign substance. The immune cells overreact to substances that are normally harmless. During the allergic reaction, the body releases chemicals that trigger symptoms that can than affect the eyes, nose, and throat, as well as the skin and the lungs. Even a trace amount of the allergen can cause a reaction in sensitive individuals.
Food allergens are the parts of foods (usually proteins) that cause allergic reactions. Most allergens can still cause allergic reactions even after they are cooked or have been digested. However, some allergens (usually from fruit and vegetables) only cause allergic reaction when they are eaten raw. Such reactions are generally limited to the mouth and throat.
Trace amounts of food allergens may also trigger reactions in some patients. For instance, patients who are allergic to peanuts may develop an allergic reaction after eating food that has been manufactured in the same facility as peanuts. Some patients may develop an allergic reaction if a kitchen utensil touched a food allergen and then touched their food. It is also possible to have an allergic reaction after smelling food allergens.
The severity and duration of allergy symptoms vary among patients. Symptoms can develop anywhere from several minutes to several hours after exposure to the food allergen. Anaphylaxis is the most severe type of allergic reaction that may occur. The most serious symptoms of anaphylaxis include low blood pressure, breathing difficulties, shock, and loss of consciousness, all of which can be fatal. About 30,000 Americans need emergency room treatment and 150 die each year because of allergic reactions to food, according to the U.S. Food and Drug Administration (FDA).
Certain food allergies, including allergies to peanuts, tree nuts, and/or shellfish, may have longer-lasting effects. However, new studies show that up to 20% of people who are allergic to these foods may lose their allergic sensitivities over time.
Food allergy is usually prevalent among individuals who have a family history of allergies. About eight percent of children, and two percent of adults in the United States are estimated to have food allergies. Food allergies are most common during the first few years of life, and allergic sensitivity declines over the first decade of life for most patients.
To help patients avoid known food allergens, the U.S. Congress passed the Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA). The law, which went into effect January 1, 2006, requires food manufacturers to clearly state on their packages whether the food is made with any ingredients that contain protein from the eight major allergenic foods. These foods include: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, and soybeans.

Author information

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography

American Academy of Allergy Asthma & Immunology. .
American College of Allergy, Asthma & Immunology. .
Eigenmann PA. The spectrum of cow's milk allergy. Pediatr Allergy Immunol. 2007 May;18(3):265-71. .
Natural Standard: The Authority on Integrative Medicine. .
Taylor SL, Hefle SL. Ingredient and labeling issues associated with allergenic foods. Allergy. 2001;56 Suppl 67:64-9. .
The Food Allergy and Anaphylaxis Network. .
Ring J, Mohrenschlager M. Allergy to peanut oil - clinically relevant? J Eur Acad Dermatol Venereol. 2007 Apr;21(4):452-5. .
U.S. Food and Drug Administration. .

Causes

Most allergies are inherited, which means they are passed on to children by their parents. Although people inherit a tendency to be allergic, they may not inherit an allergy to the same allergen. When one parent has allergies, each of his/her children has a 50% chance of developing allergies. That risk increases to 75% if both parents have allergies.
Typically, an allergic response is not triggered the first time the body encounters the allergen. The immune system may become sensitized the first, or several times after the body is exposed to an allergen. During this process, the body's white blood cells develop immunoglobulin E (IgE) antibodies to the allergens. Once sensitized, the antibodies quickly detect and bind to the allergens in the body. These antibodies also trigger the release of chemicals (like histamine) that cause allergic symptoms, such as runny nose and sneezing.

Symptoms

General: There is a broad range of allergy symptoms experienced by both adults and children with food allergies. Symptoms can develop anywhere from several minutes to several hours after ingestion.
Anaphylaxis (anaphylactic reaction): Anaphylaxis is a systemic allergic reaction, which means that many parts of the body are affected. Symptoms of anaphylaxis can vary from mild to severe and may be potentially life threatening. The most dangerous symptoms are low blood pressure, breathing difficulties, shock, and loss of consciousness, all of which can be fatal. The time lapse between ingestion/or contact with the allergen and anaphylactic symptoms varies among individuals. Symptoms may appear immediately or may be delayed from 30 minutes to one hour after exposure. Symptoms may also disappear and then recur hours later. Once symptoms arise, they progress quickly.
Asthma:Asthma symptoms, including coughing, wheezing, shortness of breath, or difficulty breathing, may be triggered by food allergies, especially in infants and young children.
Atopic dermatitis (eczema): Eczema, which is itchy, scaly, red skin, may also be triggered by food allergy. Others may experience itchy skin or facial flushing.
Gastrointestinal symptoms: Gastrointestinal symptoms may include vomiting, diarrhea, gas, and abdominal cramping. Some patients may develop a red rash around the mouth, as well as swelling of the mouth, stomach, and throat.
Hives: Hives are the most common allergic skin reaction associated with food allergies. Hives are red, itchy swollen welts on the skin that may appear suddenly and disappear quickly. They often develop in clusters, with new clusters appearing as other areas clear up.

Diagnosis

A specialized type of doctor called an allergist or immunologist is the best-qualified medical professional to diagnose food allergy. First, the allergist/immunologist will take a thorough medical history, followed by a physical examination. The allergist will ask for detailed information about the types of foods consumed, as well as the frequency, severity, and type of symptoms. The amount of time between food consumption and allergy symptoms will also be considered.
If food allergy is suspected, a skin test or allergen-specific immunoglobulin (IgE) test will then be conducted to determine specific food allergens.
Skin test: A skin test is used to determine whether a patient is allergic to certain foods. During the test, the skin is exposed to different food allergens. The skin is then observed for an allergic reaction. If an allergen triggers an allergic reaction to a test, the patient will develop reddening, swelling, or a raised, itchy red wheal (bump) that looks similar to a mosquito bite. The healthcare provider will measure the size of the wheal and record the results. The larger the wheal, the more severe the allergy. A skin test is typically conducted in a healthcare provider's office. Skin tests cause minimal, if any, discomfort. The needles used barely penetrate the skin's surface and will not cause bleeding.
Allergen-specific immunoglobulin (IgE) test: An allergen-specific immunoglobulin E (IgE) test, commonly referred to as radioallergosorbent test (RAST?), may also be used to determine whether the patient is allergic to certain foods. However, this test is less accurate than a skin test. It is usually performed in patients who have coexisting severe skin diseases (like eczema or psoriasis) that make it difficult to interpret a skin test.
The in vitro test is conducted in a laboratory. During the procedure, a sample of blood is taken from the patient. The blood is then sent to a laboratory that performs specific IgE blood tests. The allergen is bound to an allergosorbent (paper disk). Then the patient's blood is added. If the blood contains antibodies (immunoglobulins that detect and bind to antigens) to the antigens, the blood will bind to the allergen on the disc. A radiolabelled ANTI-IgE antibody is then added to the disc to measure the level of immunoglobulin E present in the blood. The higher the radioactivity, the higher the level of IgE in the blood and the more severe the allergy.
A qualified healthcare provider will interpret the results of the test. In general, the sensitivity of these tests range from 50-90%, with the average being about 70-75%. The patient will receive test results in about seven to 14 days.

Treatment

Epinephrine: Epinephrine is only used to treat very severe reactions, including anaphylaxis. Epinephrine is injected and acts as a bronchodilator because it dilates the breathing tubes. It also constricts the blood vessels, which increases blood pressure. Patients who experience anaphylaxis may also be admitted to the hospital to have their blood pressure monitored and possibly to receive breathing support. Other emergency interventions may also include endotracheal intubation (placing a tube through the nose or mouth into the airway) or emergency surgery to place a tube directly into the trachea (tracheostomy or cricothyrotomy).
Individuals with a history of severe food allergies should carry a prescription epinephrine auto-injector. If symptoms of anaphylaxis appear after exposure to an allergen, the patient uses the device to inject the epinephrine into his/her thigh. A trained family member of friend may help the patient administer the epinephrine, if necessary.
Less severe allergic reactions that affect breathing may be treated with an inhaled epinephrine bronchodilator.
Antihistamines: Antihistamines like diphenhydramine reverse the actions of histamine and help reduce allergy symptoms. Diphenhydramine is injected when quick action is needed during a severe allergic reaction. It may be given by mouth for a less severe reaction.
Corticosteroids: Corticosteroids are usually given through an IV (intravenously) at first in order to quickly reverse of the effects of the mediators (like histamine). These drugs reduce swelling and many other symptoms of allergic reactions. Individuals may also need to take a corticosteroid in pill form for several days after the initial treatment. These drugs are often given for less severe reactions. Also, a corticosteroid cream or ointment may be used for skin reactions.

Integrative therapies

Note: Anaphylaxis is considered a medical emergency that requires immediate medical care. Therefore, integrative therapies should not be used in place of conventional medicine when an individual has an anaphylactic reaction.
Unclear or conflicting scientific evidence:
Acupuncture: Acupuncture plus point-injection has been found beneficial for the treatment of hives, although more research is needed to confirm these findings.
Needles must be sterile in order to avoid disease transmission. Avoid with valvular heart disease, infections, bleeding disorders, or with agents that increase the risk of bleeding (anticoagulants), medical conditions of unknown origin, and neurological disorders. Avoid on areas that have received radiation therapy and during pregnancy. Use cautiously with pulmonary diseases (like asthma or emphysema). Use cautiously in elderly or medically compromised patients, diabetics, or with history of seizures. Avoid electroacupuncture with arrhythmia (irregular heartbeat) or in patients with pacemakers.
Applied kinesiology: Applied kinesiology (AK) is commonly used for food allergy diagnosis. However, evidence is mixed as to whether AK can aid in this type of assessment.
Applied kinesiology techniques in themselves are considered harmless. However, medical conditions should not be treated with AK alone, and AK should not delay appropriate medical treatment.
Lactobacillus acidophilus: Lactobacilli are bacteria that normally live in the gastrointestinal tract, mouth, and vagina. There is conflicting information from several human studies as to whether using Lactobacillus acidophilus by mouth is helpful for lactose intolerance. More research is needed before a conclusion can be drawn.
L. acidophilus may be difficult to tolerate if allergic to dairy products containing L. acidophilus. Avoid with a history of an injury or illness of the intestinal wall, immune-disease, or heart valve surgery. Avoid with prescription drugs, like corticosteroids, because of the risk of infection. Use cautiously with heart murmurs. Antibiotics or alcohol may destroy Lactobacillus acidophilus. Therefore, it is recommended that Lactobacillus acidophilus be taken three hours after taking antibiotics or drinking alcohol. Some individuals can use antacids (like famotidine (Pepcid?), esomeprazole (Nexium?)) to decrease the amount of acid in the stomach one hour before taking Lactobacillus acidophilus.
Probiotics: Probiotics are beneficial bacteria and are sometimes called friendly germs. They help maintain a healthy intestine by keeping harmful bacteria and yeasts in the gut under control. Most probiotics come from food sources, especially cultured milk products. Probiotics can be taken as capsules, tablets, beverages, powders, yogurts, and other foods. Supplementation of infant formulas with probiotics is a potential approach for the management of cow's milk allergy, but there is conflicting evidence as to whether it improves lactose intolerance. More research is needed in this area before a conclusion can be drawn.
Probiotics are generally considered to be safe and well-tolerated. Avoid if allergic or hypersensitive to probiotics. Use cautiously if lactose intolerant. Caution is advised when using probiotics in neonates born prematurely or with immune deficiency.

Prevention

Avoid known food allergens: Avoiding known food allergens is the best way to prevent an allergic reaction from occurring.
Ask about ingredients: To avoid eating a food allergen, individuals should always ask about ingredients in the food when dining at a restaurant or someone else's home. Even a trace amount of the allergen can cause a reaction in sensitive individuals.
Read food labels: Patients who have food allergies should carefully read food labels.
Many countries, including the United States, have food labeling laws that require manufacturing companies to list all food allergens in common language, rather than scientific or technical terms.
Some ingredients, such as hydrolyzed proteins, edible oils, lecithin, lactose, starch, flavors, and gelatin may be derived from food proteins known to cause allergic reactions in sensitive individuals. To help patients avoid known food allergens, the U.S. Congress passed the Food Allergen Labeling and Consumer Protection Act of 2004 (FALCPA). The law, which went into effect January 1, 2006, requires food manufacturers to clearly state on their packages whether the food is made with any ingredients that contain protein derived from the eight major allergenic foods. These foods include, milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, and soybeans.
Be prepared for emergencies: Anaphylactic reactions caused by food allergies can be potentially life threatening. Individuals who have experienced anaphylactic reactions should avoid allergy-causing food. Individuals with a history of anaphylaxis should carry an autoinjectable epinephrine device (known as an EpiPen?) with them at all times. A trained family member or friend may help the patient administer the epinephrine, if necessary.
Individuals with food allergies should also wear an identification bracelet that describes the allergy.
If children have allergies, their baby-sitters, teachers, and other caretakers should be informed of their allergies.

Children and food allergy

According to the American Academy of Allergy Asthma & Immunology (AAAAI), six foods cause 90% of food allergies in children. These six foods are milk, peanuts, soy, eggs, wheat, and tree nuts (like pecans and walnuts). Children usually outgrow allergies to milk, eggs, and soy. However, allergies to peanuts, tree nuts, fish, and shellfish continue throughout adulthood.
Children with skin disorders (like eczema or psoriasis) are more likely to develop food allergies. In fact, food allergies are seen in about 35% of children with eczema.
Children who have allergic reactions to inhaled substances, such as dust, mold spores, or pollen, also have an increased risk of developing food allergies.
Low-dose exposure of peanut protein or peanut oil products may cause peanut allergies in children, according to one study. According to the American Academy of Pediatrics, children should not consume peanuts or peanut-containing products until they are three years old if they have experienced other food allergies. Strawberries should also be avoided until the baby is about 10-12 months old.
Children whose mothers have food allergies are more likely to inherit the allergy if born by cesarean section, according to one study. One study of children with allergic mothers who had C-section deliveries found that the babies were seven times more likely to develop food allergies than predisposed children who were born vaginally.

Cross reactivity and oral allergy syndrome

In some cases, an allergy to one food may result in sensitivity to similar foods because they share the same or similar proteins. For instance, consuming cross-reactive proteins that are found in foods like peaches, apples, pears, and cherries will cause itchiness of the mouth and throat in people who are allergic to birch tree pollens.
Some patients who experience seasonal allergy symptoms may experience a worsening of symptoms after eating fresh fruits. This is called oral allergy syndrome.

Common food allergens

General: The most common food allergens are the proteins in cow's milk, eggs, peanuts, wheat, soy, fish, shellfish, and tree nuts.
In some food groups, especially tree nuts and seafood, an allergy to one food may cause the patient to be allergic to all the members of the same group. This is known as cross-reactivity. However, it is also possible to be allergic to both peanuts and walnuts, which are from different food families.
Cross-reactivity is not as common in the meat food group. For instance, many patients who are allergic to eggs can eat chicken, and many patients who are allergic to cow's milk can eat beef.
Cow's milk: Although individuals of any age can develop allergies to cow's milk, it is most common among infants. It is estimated that two to three percent of infants have a milk allergy, but they typically outgrow it by the time they reach three to five years old. Breastfed infants are less likely to develop allergies to cow's milk than those who are not. Allergy symptoms may develop immediately after ingesting milk or as long as seven days after consuming cow's milk. Mother's of an allergic infant should limit their intake of cow's milk. The protein in cow's milk that causes the allergic reaction may pass from the mother to her baby via breastfeeding.
Eggs: Most individuals who are allergic to eggs are allergic to the protein in egg whites. However, some patients cannot tolerate the egg yolks either. An allergic reaction can also occur if the eggs are cooked or prepared with other foods. In fact, some patients develop an allergic reaction just by smelling or touching eggs. Most allergic reactions develop minutes to hours after ingesting or coming into contact with eggs or food made with eggs. Symptoms generally subside in less than one day.
Peanuts: Peanut allergy is the number one cause of severe or fatal allergic reactions in children and adults in the United States. Peanut allergy causes 15,000 emergency room visits each year and is responsible for nearly 150 deaths nationwide. Even a trace amount of the food can cause a serious reaction in sensitive individuals. Less than 21% of patients with peanut allergy will outgrow it.
When allergic individuals consume peanuts or peanut-containing foods, an anaphylactic reaction takes place. This is a serious, life-threatening reaction that affects many parts of the body. Symptoms of an anaphylactic reaction include itching, hives over large areas of the body, swelling in the throat or tongue, difficulty breathing, dizziness, stomach cramps, nausea, or diarrhea.
Despite the increase in peanut allergies over the years, the exact cause remains unknown. Some research believe they may be inherited or due to prenatal exposure to peanuts. They may also be caused by exposure to peanut oils (from products like diaper creams) on an infant's skin.
Wheat: An allergic reaction to wheat occurs when the body's immune system overreacts to a protein in wheat called gluten. Gluten is found in products such as wheat, rye, barley, and oats. However, some patients are able to tolerate oats. Modern wheat products are manufactured to contain high amounts of gluten. Celiac disease is not the same as wheat allergy because it does not involve the body's immune system.
Soy: The proteins in soy can cause an allergic reaction in sensitive people. Soy products are used in many manufactured products. Also, many fast food restaurants use soy products in their foods. Therefore, patients who are allergic to soy should always read food labels carefully and ask about ingredients. Many medications, including Benadryl? Fastmelts, contain soy proteins. Therefore, patients who are allergic to soy should consult their healthcare providers and pharmacists before taking medications.
Some patients may be able to tolerate some soy products. For instance, soybean oil does not usually cause an allergic reaction because it does not contain the soy proteins responsible for such a response. Also, some fermented soy foods like miso and tempeh may cause a more mild allergic reaction than whole soybeans. Patients who are allergic to soy may also react to other similar foods, such as peanuts, green peas, lima beans, chickpeas, wheat, string beans, rye, and barley.
Fish: Allergic reactions to fish are often severe, and they are usually life-long. Individuals can develop a severe allergic reaction after coming into contact with just trace amounts of the allergen. Some patients may develop a reaction after inhaling the fumes of fish that is being cooked. Therefore, individuals who are allergic to fish should avoid seafood restaurants. Even if the patient orders a non-fish meal, there is a significant risk that a kitchen utensil (like a spatula whisk or spoon) may have come into contact with fish. Patients may be allergic to one or more types of fish. Patients can be tested to determine their exact fish allergies.
Shellfish: Most people are only allergic to one type of shellfish; either crustaceans (like shrimp, crabs or lobsters) or mollusks (like clams, oysters, or muscles). Crustaceans are more likely to cause an allergic reaction. Some patients may be allergic to both types of shellfish. Shellfish allergies may be severe, and they are typically life-long. Even trace amounts of shellfish are capable of inducing a severe allergic reaction. Some patients may develop a reaction after inhaling the fumes of shellfish that is being cooked. Therefore, individuals who are allergic to shellfish should avoid seafood restaurants. Even if the patient orders a non-fish meal, there is a significant risk that a kitchen utensil (like a spatula, whisk, or spoon) may have come into contact with shellfish. Also, imitation shellfish (like imitation crab meat) might contain trace amounts of shellfish. Many manufacturing companies add shellfish for flavoring.
Tree nuts: Tree nut allergies are often severe, and they are typically life-long. Even trace amounts of tree nuts can cause an allergic reaction in sensitive people. Examples of nuts in the tree nut family include walnuts, pecans, pistachios, cashews, Brazil nuts, beechnuts, chestnuts, hazelnuts, filbert nuts, hickory nuts, almonds and macadamia nuts. Patients can be tested to determine the nuts they are allergic to. Some patients who are allergic to tree nuts may be able to tolerate peanuts. Others cannot tolerate either.

Food intolerance

General: Food intolerance is different than a food allergy because it does not involve the immune system. Food intolerance refers to an abnormal response to food or food additives that is not an allergic reaction. Also, unlike food allergies, which may be potentially fatal, food intolerance is generally not life threatening.
For instance, patients who are lactose intolerant may experience abdominal pain and cramping after consuming milk because the patients lacks the enzymes necessary to break down milk sugar for digestion. Since the immune system is not involved in the reaction, it is not an allergic response.
Food additives: Food additives are substances or chemicals that are added to food to make it last longer, taste better, or look more appealing. Some individuals develop adverse reaction to food additives.
Consuming large amounts of food additives may produce symptoms that appear similar to allergic symptoms. The most common foods additives that cause intolerance include yellow dye number 5, monosodium glutamate (MSG), and sulfites.
In rare cases, yellow dye number 5 has caused hives in sensitive people.
MSG, which is used to enhance the flavor of foods, can cause flushing, sensations of warmth, light-headedness, headache, facial pressure, chest pain, and feelings of detachment when consumed in large amounts. These symptoms are temporary and occur soon after consuming large amounts of food that contains MSG.
Sulfites occur naturally in some foods, and they are sometimes added to food to prevent mold growth or enhance crispness. However, high concentrations of sulfites can cause the airways to constrict in asthma patients. The sulfites emit a gas called sulfur dioxide, which the asthmatic inhales while eating the food. This gas irritates the lungs and may make it difficult to breathe. Consequently, the U.S. Food and Drug Administration (FDA) banned sulfites that were used as spray-on preservatives for fruits and vegetables. However, sulfites are still added to some foods. They also form when wine ferments.
Food poisoning: Another type of food intolerance is called food poisoning. Food poisoning usually occurs after consuming food that is contaminated with microorganisms like bacteria. Ingesting contaminated food can produce symptoms that appear similar to food allergy.

Who should consult an allergist

Individuals with a diagnosed food allergy.
Individuals who have limited diets based on perceived side effects of foods.
Individuals with a family history of allergies.
Individuals who are pregnant or have a newborn.
Individuals who have experienced allergic symptoms (such as hives, itching, wheezing, gastrointestinal responses) linked to certain food exposure.
Individuals who experience itchiness in their mouth after eating raw fruits and vegetables.
Infants and elderly patients with acid reflux disease that does not respond to treatment (especially if it is difficult to swallow).
Infants with unexplained gastrointestinal symptoms, such as vomiting, diarrhea (especially if there is blood in the stool), poor growth, and/or poor absorption, which do not respond to medical treatment.
Individuals who have an inflamed gut caused by an increase of white blood cells called eosinophils.