Food allergy

What are food allergies?

Food allergies are a group of closely related responses that involve an allergic reaction to a specific food. Roughly 1 to 2 percent of adults and 3 to 8 percent of children are estimated to have true food allergies, according to Asthma and Allergy Foundation of America.

An allergic response to a food or food ingredient involves the immune system’s exaggerated response to a food protein. The body produces immunoglobulin E (IgE) antibodies against the food. These IgE antibodies attach to the body’s mast cells, a type of white blood cell that contains chemicals called histamines and leukotrienes.

The next time IgE antibodies come in contact with the offending food molecule, these chemicals are released, causing symptoms ranging from mild (e.g., itching, hives) to severe and life-threatening anaphylactic shock, which is characterized by difficulty breathing and dangerously low blood pressure.

There is no way to know whether a person with a food allergy is likely to have a mild or severe reaction after eating the problem food. Reactions can be fatal and individuals with a food allergy must completely avoid all foods to which they are allergic. Food allergies can be triggered by even tiny amounts of a problem food.

It is important to note that allergic individuals do not necessarily have to ingest a food allergen to have a reaction. Even touching another person who has recently consumed a problem food can bring on a reaction in some people. These sensitive individuals must be very careful not to have skin contact with any type of product containing the allergen and should also be careful not to inhale fumes produced by the food.

There are several conditions that may predispose an individual to develop food allergies. People with a family history of hay fever, asthma, hives or eczema have an increased likelihood of having a child who will develop food allergies. Age is also a factor. Although food allergies affect people of all ages, they are most common in toddlers and infants.

Several food allergies that are typically prevalent in children gradually go away as children grow older. For instance, food allergies to milk, eggs, wheat and soy, are common in the first few years of life, but are often outgrown over the next 10 years. This is because the body is less likely to absorb food proteins that trigger allergies as the digestive system matures over time.

However, certain food allergies, such as those related to peanuts, tree nuts, fish and shellfish, are likely to persist throughout adult life. Food allergies can also develop during adulthood. Unlike children, adults do not usually lose their sensitivity to food allergens.

It is important to note that not all reactions to food are allergic reactions. Related issues that may be confused with food allergies include food intolerances, food poisoning, sensitivity to food additives and other problems.

Potential causes of food allergies

Eight types of food are responsible for triggering almost 90 percent of known food allergies, according to the Food Allergy and Anaphylaxis Network.

They are:

  • Milk. Includes cheese, butter, cream, casein (a milk protein) and whey. A milk allergy should not be confused with milk intolerance, which is an inability to digest milk and not a true allergy.
  • Wheat. Includes crackers, pastas, bread and malt. A wheat allergy should not be confused with gluten intolerance, which is a sensitivity to the protein gluten and not a true allergy.
  • Soy. Includes lecithin (a food ingredient often made from soy), some types of baked foods, canned tuna, sauces and baby formulas.
  • Peanuts. Includes peanut butter, “gourmet” peanut oil (includes cold-pressed, expelled or extruded), many types of ethnic foods (including Chinese, Indonesian, Thai, Vietnamese and possibly Mexican) and some flavorings.
  • Tree nuts. Includes hazelnuts, cashews, almonds, walnuts, pecans, Brazil nuts and others.
  • Shellfish. Includes crab, crayfish, shrimp, clams and lobster.
  • Fish. Includes yellowtail, salmon, mackerel, tuna and hake.
  • Eggs. Includes commercially processed cooked pastas, mayonnaise and some brands of egg substitutes.

Other food allergies are less common, but significant because of the popularity of their trigger foods:
  • Corn. This allergy is triggered by corn protein and is notable because of the large number of food products that contain corn-based ingredients.
  • Rice. This rare allergy can be triggered through both ingestion and inhalation (of rice pollen). It has a much more common occurrence in geographies where rice is regularly served – such as Japan.
Among adults, shellfish, peanuts, tree nuts and fish are among the most common triggers for food-related allergic reactions. In children, eggs, milk, peanuts, soy and wheat are most often the cause.

As noted earlier, even trace amounts of an allergen can provoke a reaction. For instance, foods sold in bakeries and ice cream parlors often come into contact with surfaces contaminated with peanuts. Processed foods also may come into contact with allergen particles. In both cases, this can be enough to cause an allergic reaction in highly susceptible individuals.

Some people have expressed concern over the dangers potentially posed by the increasing use of genetically modified foods (GMOs). While there have been no studies to indicate GMOs are dangerous, the introduction of new kinds of proteins could trigger previously unknown types of allergies in some people. Research designed to guard against the release of any new genetically modified allergens is ongoing.

Clinical research suggests that a nursing mother who has a history of allergies in her family may be able to prevent or delay passing on a food allergy to her child by avoiding common trigger foods. By staying away from foods such as milk, soy, eggs and peanuts, a nursing mother may keep her young child free of the proteins that can trigger a food allergy. Though physicians almost unanimously agree that there are benefits to children who are breastfed, there is currently no clinical evidence that this method can, in fact, prevent allergies in children.

Related allergies and conditions

Individuals who have exhibited a history of allergies, eczema or asthma are more likely to have a food allergy. These individuals are also more likely to have a severe or life-threatening reaction, such as anaphylactic shock.

Several related conditions may be mistaken for a food allergy.

These include:

Food intolerances

These conditions involve the body’s inability to breakdown specific food substances (such as lactose with milk intolerance) – rather than an allergic response to the food in question. With lactose intolerance, for example, a person lacks sufficient amounts of the enzyme lactase, which makes it possible to breakdown the lactose in milk. Symptoms of food intolerances generally involve discomfort, such as stomach cramps, bloating, diarrhea or gas. However, they are very rarely severe or potentially life-threatening. Also, people with food intolerances can often enjoy small quantities of the problem food without risk. People with food allergies need to completely avoid even trace amounts of the problem food.

Food poisoning

Food poisoning can also imitate an allergic reaction. But, while the symptoms might appear similar, the body is not producing an actual allergic reaction in these instances. Rather, it is responding to harmful bacteria or other toxins within contaminated or spoiled foods. Reactions can be severe and may therefore be confused with food allergies.

Additive sensitivity

Food additives are substances added to food for better preservation, taste and color. Some people have reported experiencing reactions to certain additives when ingested (e.g., MSG). However, there is currently no clinical proof that confirms the existence of this type of sensitivity. More research is needed on this subject before the medical community can confirm or reject this condition.

Irritable syndrome bowel

A disorder in which the large intestine (colon) does not function normally, leading to cramping, abdominal pain, bloating, constipation and/or diarrhea. Because specific types of food will sometimes trigger irritable bowel symptoms, this condition may be confused with a food allergy.

Other gastrointestinal conditions

Some kinds of cancers, inflammatory bowel disease and ulcers of the gastrointestinal tract can produce symptoms similar to those experienced with food allergies. These symptoms can include vomiting, diarrhea or cramping abdominal pain that gets worse when eating.

Stress or psychological issues

Though the relationship between stress and allergy symptoms is not entirely clear, some individuals will feel sick simply by thinking about a certain type of food.

Cross-reactivity can occur when a person who already has one known type of food allergy seems susceptible to a chemically related food or other allergen. For example, someone with a strong reaction to wheat may also be allergic to oats. For individuals with severe allergic reactions, a physician will often suggest avoiding related food types.

Cross-reactivity can also occur with nonfood allergies. For instance, most people with latex allergies react only to the natural latex protein found in latex products. However, some of these individuals find they are also allergic to fresh fruits, vegetables and nuts. This occurs because the protein in latex is so similar to the proteins found in the fruits, vegetables and nuts that the body is unable to distinguish between them.

Other conditions associated with food allergies include:

Oral allergy syndrome

This cross-reactive condition involves an allergic reaction being triggered in an individual who is allergic to pollen or another airborne allergen. Fresh fruits, vegetables and nuts can all have allergens similar to some airborne allergens. When these foods are eaten the allergens come into contact with the lining of the mouth and throat, resulting in itching or swelling of the lips, tongue or throat. In this case, the immune system confuses the allergens in the fruit with the airborne allergens.

Exercise-induced food allergy

An exercise-induced food allergy is usually triggered when an individual exercises after eating a specific kind of food. People who are susceptible to this kind of reaction can avoid problems by eating at least two hours before exercising.

Infantile colic

This condition is sometimes associated with food allergies. An allergy to milk or soy may be responsible for up to one in five cases of colic in infants. This likely comes as a result of the immaturity of the immune system in infants with these allergies.

Signs and symptoms of food allergies

A food-related allergic reaction usually occurs anywhere from a few minutes to a few hours after eating the problem food. These reactions can range from mild to severe and potentially life-threatening anaphylactic shock. Symptoms may involve the eyes, nose, throat, skin, respiratory system and digestive system.

Mild to moderate symptoms of an allergic food reaction may include:

  • Skin conditions, including hives and rashes of raised bumps
  • Itchy or watery eyes
  • Runny nose or nasal congestion
  • Swelling, commonly around the lips and mouth
  • Itching or tingling in the tongue and lips
  • Hoarseness
  • Wheezing
  • Abdominal cramps
  • Nausea or vomiting
  • Diarrhea

Mild to moderate symptoms may progress rapidly to more severe symptoms. Therefore, people having any kind of food reaction should seek immediate medical attention to prevent anaphylactic shock. It is also possible for severe symptoms to appear even when mild to moderate symptoms are not present.

Signs and symptoms of a more severe reaction include:

  • Difficulty breathing
  • Shortness of breath
  • Tightness in the chest or throat
  • Choking
  • Drop in blood pressure
  • Rapid pulse
  • Dizziness or lightheadedness
  • Fainting

People who suspect a food allergy should consult an allergist/immunologist.

Diagnosis methods for food allergies

The first step a physician is likely to take in the diagnosis of a food allergy is to create a detailed medical history and dietary history of the patient. The history may include the following information:

  • Timing of the reaction (e.g., whether the reaction occurred within an hour of eating)
  • Whether the reaction is always associated with a certain food or food group
  • How much of the food was consumed, because the severity of a reaction may relate to the amount of food consumed
  • How the food was prepared (e.g., was it consumed raw or thoroughly cooked)
  • Were symptom relief measures successful (e.g., if taking antihistamines relieved the symptoms)
The physician will also perform a physical examination to help identify or exclude medical problems that may be causing the patient's symptoms. By gathering this basic information, a physician can get a better idea of where to proceed with further evaluations. This may include attempts to identify the specific allergen to which the patient is sensitive. Such procedures are not definitive, but can provide information that is relevant to the patient’s condition and useful in designing treatment plans.

These measures may include:

Skin test

This test involves pricking the patient’s skin with food extracts. The skin will react with redness and swelling for those extracts capable of eliciting an allergic reaction when consumed. This accuracy of this test's results will vary depending on the food being tested.

RAST (radioallergosorbent test)

This type of blood test allows a laboratory to directly test a blood sample for antibodies that correspond to specific foods. While less sensitive than a skin test, it can be used on individuals who have reactions too severe for a skin test. The RAST test is also a good option for infants, or individuals with skin disorders such as eczema.

Oral food challenge

Also called the double-blind food challenge, this is considered the most effective way of determining the cause of a food allergy because it supplies the most convincing results. Different foods are placed within capsules to hide their identity. Neither the patient nor the physician knows which capsule contains the suspected allergen. The patient consumes the capsules and the physician looks for signs of an allergic reaction. This type of test is time-consuming and difficult. It is often reserved to confirm suspicions that a patient's symptoms are not caused by a food allergy. This type of test should only be performed in the presence of a physician who can treat anaphylaxis.

Elimination diet

This process involves removing suspect foods from a patient’s diet to see if the allergic reactions persist. Foods are removed on a trial-and-error basis for a period of time. The results of the diet make it easier to confirm, rule out or permanently remove a problem food.

People should not attempt to “self-diagnosis” their food allergy by eliminating foods on their own. Performing an elimination diet without the supervision of a physician can lead to an unbalanced diet and a number of resulting health problems.

Physicians may also ask their patients to keep a food diary over the period of a week or two. While keeping the diary, patients will note all of the foods they eat, the symptoms they experience and when the symptoms occur. This information can be used in combination with findings from the medical history, physical exam and allergy tests to determine the particular food that is triggering symptoms.

Treatment options for food allergies

The only form of treatment for food allergies is the complete removal of problem foods from the diet. There are currently no drugs available that can prevent a food allergy from taking place. Food allergies can be deadly if avoidance is not practiced diligently.

Once a physician has helped a patient determine which foods are allergy triggers, people must remove these foods from their diet by paying close attention to the ingredients in the foods they eat. By checking the ingredient labels on foods at the grocery store, and asking about ingredients and preparation techniques at restaurants, people can successfully avoid problem foods and control their food allergy.

To be sure that a problem food is not consumed by accident, people should also learn alternate names of the food. For example, those allergic to milk must also avoid anything with casein, which is a milk protein. New legislation may make it easier for people to determine if a food item contains a potential allergen. As of January 2006, the Food and Drug Administration (FDA) is requiring food manufacturers to list food allergens on their product labels.

Though some allergies are outgrown, many kinds of food allergy persist throughout adulthood. Fortunately, avoiding food allergens is a way for allergic individuals of all ages to prevent an allergic reaction from ever taking place.

Although preventive measures can be taken to reduce the likelihood of ingesting a problem food, accidental consumption can still occur. For this reason, individuals who are highly sensitive to a food allergen should carry injectable epinephrine with them at all times. This drug can be used to quickly counteract the effects of the life-threatening condition known as anaphylactic shock. These sensitive individuals should also wear a medical alert bracelet or necklace that can identify their condition to healthcare workers.

Parents of children with food allergies should alert their child's day care center or school to the allergies. They should also provide the staff with written instructions on how to properly identify and treat the child's allergic reaction. Other adults who have frequent contact with the child, such as parents of the child’s friends, coaches and babysitters, should also be prepared to respond quickly to a reaction.

Symptom relief for food allergy reactions

The only effective treatment for a food allergy is the complete removal of food allergens from the diet. The diligent practice of avoidance is a necessity for anyone suffering from a food allergy.

Once an allergic reaction to a food has occurred, however, there are some alternatives for the relief of allergy symptoms. These medications can help relieve symptoms somewhat, but are by no means a cure for the condition. These medications should not be viewed as a countermeasure or effective antidote for food allergies. Only avoidance of problem foods can successfully treat a food allergy.

Though some medications for the relief of allergy symptoms are available over-the-counter, they should be used only under the direction of a physician. Some medications that may be recommended include:


Medications that provide relief for more common allergy reactions such as hives, sneezing, runny nose and gastrointestinal symptoms. Antihistamines directly counteract the effects of the histamines, which are chemicals responsible for most allergy symptoms. With mild symptoms, these drugs are usually administered orally. For more severe allergic reactions, a physician may recommend an injected form of antihistamine.


Medications that open the airways of the lungs, relieving symptoms such as shortness of breath or wheezing. They may be recommended for people whose food allergies trigger asthma attacks or asthma-like symptoms. They are usually breathed directly into the lungs using an inhaler.

Epinephrine injection

A synthetic form of adrenaline that, when injected, is a powerful bronchodilator, opening breathing tubes and restoring normal respiration quickly. It is used for the most severe allergic reactions involving life-threatening anaphylactic shock. Most physicians recommend that individuals who are susceptible to severe reactions carry an injection of epinephrine with them at all times and understand how to self-administer the drug. A medical alert bracelet or necklace is also a good idea for these individuals.


Medications that reduce inflammation. These medications are most commonly used to treat severe allergic reactions in infants.

Questions for your doctor about food allergies

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to food allergies:

  • What symptoms may indicate that I am having an allergic reaction to a food?
  • How can we be sure my reactions are from food allergies? Can we determine which foods are causing the reaction?
  • What food allergy treatment options are available to me? Are there any over-the-counter or prescription medications that may aid in relieving symptoms?
  • When should I seek medical treatment for a food-related allergic reaction?
  • Is it safe for me to occasionally eat a small portion of the problem food?
  • Would you advise me to carry an epinephrine-pen in case of an allergic reaction?
  • Is this likely to be a life-long allergy?
  • Is it safe for me to prepare foods that I am allergic to for my family?
  • What should I do if I suspect that I have ingested a problem food?
  • How likely is it that I will pass this allergy on to my children?