Food Allergies: An Overview

Posted on August 13, 2018

Food allergy develops when a person’s immune system becomes sensitized to proteins from a certain food. Whenever the person eats the allergenic food, the immune system launches an abnormal reaction as though the food were a dangerous invasive particle such as a virus, bacterium, toxin, or parasite. Food allergies can cause a huge range of symptoms, which may be mild or severe. An allergenic food may cause a mild reaction in a person one day and a severe one in the same person the next day.

What is a food allergy?

Our immune systems have many different types of defenses designed to protect us against infections. Each defense has a different way of responding to attacks from foreign particles, or antigens. One of the most important defenses our bodies have is antibodies (also called immunoglobins or Ig) produced by white blood cells called B cells. Antibodies are proteins that can recognize specific antigens and launch an attack against them. The first time B cells come into contact with an antigen, they memorize the makeup of the particle. In the case of food allergies, the antigen is a protein from a particular food. On this first contact, there is no allergic reaction, but B cells begin producing antibodies called immunoglobulin E, or IgE, specific to that antigen.

The IgE antibodies circulate through the blood and collect in the skin, lungs, and mucus membranes such as those that line the nose, mouth, and throat. After this first contact, each time the antibodies come into contact with the antigen, they recognize it and launch an attack that involves triggering inflammatory chemicals – histamines, interleukins, and leukotrienes. The inflammatory chemicals flood the body, causing allergy symptoms.

The history of food allergies

Food allergies have been noted throughout history. Chinese emperors Shen Nong and Huang Di recorded their existence as early as 2,500 BCE. In ancient Greece, the philosopher Aristotle later observed that some people experienced reactions to fruit that others did not. Ancient Greek physician Hippocrates observed that certain foods could cause death in some people.

Early in the 20th century, American pediatrician Oscar Menderson Schloss developed a skin test to diagnose food allergies. The test placed extracted protein from food on the skin to observe a reaction. However, the skin test can produce false-negatives – reactions that indicate a food allergy when the person is not actually allergic. Many doctors were frustrated by the lack of accuracy.

The mid-20th century saw scientists study food allergies such as eggs, wheat, tree nuts, peanuts, and dairy. Aristotle's centuries-old observations about fruit allergies were tested in a 1942 study. The results showed that some people experience oral reactions to raw fruit, now known as oral allergy syndrome.

In the mid-1970s, American pediatrician Charles May developed the double-blind oral food challenge, which is considered the gold standard of food allergy diagnosis today. In an oral food challenge, according to Food Allergy Research & Education (FARE), the patient receives increasing doses of the suspected food allergen and a placebo (a harmless substance).

Epinephrine – also known as adrenaline – is a naturally-occurring hormone. Epinephrine was first synthesized in 1904 by German chemist Friedrich Stolz. In the 1970s, American scientists Robert Lefkowitz and Brian Kobilka studied how epinephrine works in the body. They received the Nobel Prize in Chemistry in 2012. Epinephrine is now prescribed in a pen-like device that can be automatically injected into the muscle without needing to measure the medication or prepare a syringe. Epi-Pen and other brands are prescribed to be used in cases of anaphylactic shock, a severe reaction to a food or other allergen.

Studies in the 1990s found that breastfeeding prevented atopic dermatitis and milk allergy in infants. This led to the belief that delaying an infant’s exposure to major food allergens (such as peanut, egg, and milk) would allow the immune system to “mature” and decrease the chance for food allergies later. Avoidance became standard advice from pediatricians and allergists. However, studies in 2015 and 2016 found that early oral introduction to peanuts dramatically reduced the occurrence of peanut allergy in children. Early oral introduction has not yet been proven effective with other food allergens.

Today researchers are studying a type of oral desensitization called oral immunotherapy (OIT). OIT introduces minute amounts of allergens to allergic children to build up an immune tolerance. Several studies have shown a reduction in peanut allergy severity. OIT is still in experimental stages.

How common are food allergies?

Between 4 to 6 percent of children and approximately 4 percent of adults have a food allergy. Food allergies are most common in children under age 3. Some children outgrow their food allergies. Less commonly, an adult develops an allergic reaction to a food they have eaten for years.

The prevalence of food allergies seems to be increasing, especially in Western countries such Australia, the United Kingdom, and the United States. According to the Centers for Disease Control and Prevention, reported cases of food allergies in children under 18 grew by 18 percent from 1997 to 2007 in the U.S.

Which foods cause allergies?

More than 160 different foods can cause allergic reactions. However, eight foods are responsible for 90 percent of food allergies, and reactions to these foods tend to be particularly intense. The eight major food allergens and any ingredients derived from them are listed on food labels by law in the U.S. They are:

  • Eggs
  • Fish
  • Milk
  • Peanuts
  • Shellfish
  • Soybeans
  • Tree nuts
  • Wheat

What are the possible symptoms of food allergies?

Symptoms of food allergy can vary widely. Some people develop skin symptoms such as itching, rash, or hives. Others have respiratory symptoms such as asthma, sneezing, cough, and trouble breathing. Gastrointestinal symptoms including diarrhea are also common. Others experience anxiety, behavior changes, heart palpitations, dizziness, or many other reactions.

The most serious symptom of food allergy is anaphylaxis – a life-threatening reaction characterized by a sudden drop in blood pressure, narrowing of the airways that makes it difficult to breathe, rash, and swelling. Learn more about food allergy symptoms.

Resources

External resources

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FAQs

Can you die from a food allergy?

Some food allergies can cause a potentially deadly reaction called anaphylaxis. If anaphylaxis is not immediately treated with Epinephrine followed by emergency medical treatment, it can be fatal. The U.S. Food and Drug Administration (FDA) estimates that on average, allergic reactions to food result in 30,000 emergency room visits, 2,000 hospitalizations, and 150 deaths each year.

How is a food allergy diagnosed?

There is no one test that conclusively diagnoses a food allergy. Allergists diagnose food allergies with a combination of detailed patient and family history, a physical exam, blood tests, a skin-prick test, an elimination diet, and finally a food challenge to confirm the diagnosis. Learn more about the diagnosis process for food allergies.

How is food allergy treated?

The safest and most effective way to treat food allergies is to totally avoid the allergen. Mild allergic reactions to foods may respond to antihistamines such as Benadryl (Diphenhydramine), Zyrtec (Cetirizine), or Claritin (Loratadine). People may manage specific symptoms for short periods of time with corticosteroids, which dampen the immune system and can be oral, topical, or inhaled. Severe allergic reactions such as anaphylaxis require immediate treatment with Epinephrine and a visit to the emergency room. Some people with food allergies participate in clinical trials studying pioneering new treatments for food allergies. Learn more about medications for symptoms of food allergies.

Is food intolerance the same thing as food allergy?

No, food allergy and food intolerance are not the same. Allergy and intolerance are caused by different aspects of the immune system. Food intolerance tends to cause symptoms that are mild but chronic, while food allergies tend to cause more rapid, intense reactions. Read more about differences between food allergy and food intolerance.

What causes food allergies?

There are many theories about why some people’s immune systems target food proteins and launch the process that leads to food allergies. Most researchers believe food allergies develop due to a combination of inherited and environmental factors. Read more about potential causes and risk factors for food allergies.

Can food allergies go away?

Some children outgrow food allergies. Outgrowing an allergy is defined as the ability to eat the allergenic food without experiencing a reaction. One nationwide study of more than 40,000 children showed that 26.6 percent of those with food allergies outgrew them. The average age for outgrowing the allergies was 5.4 years. The likelihood for outgrowing an allergy depends on the type of allergy and the severity of the symptoms. Egg, milk, and soy allergies were more likely to be outgrown than other common allergies. Approximately 20 percent of children with a peanut allergy outgrow it. About 14 percent of those with tree nut allergies and 4 to 5 percent of those with fish or shellfish allergies outgrow their sensitivities. The study also found that boys had a higher likelihood of outgrowing their food allergies than girls, and children of European descent had a higher likelihood of outgrowing their food allergies than children of African descent.

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