In people with a food allergy, the immune system reacts to certain proteins in food as though they were harmful pathogens, such as bacteria, parasites, or viruses.

The National Institute of Allergy and Infectious Diseases estimate that food allergies affect 4% of adults and 5% of children in the United States.

The number of reported food allergies has increased in recent years. For instance, the prevalence of peanut allergy among children has reportedly doubled over 10 years in North America.

Most food allergies develop in childhood, and children generally outgrow them, although this is not always the case. Food allergies can also develop in adulthood, but this is rarer.

In this article, we will cover the symptoms, causes, triggers, and treatment of food allergies.

Five trays of tasty bakes that cater for people's allergies. A red tray contains gluten-free banana muffins, and a plastic tub contains nut-free, low-calorie banana loaf made with stevia.Share on Pinterest
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Symptoms can range from mild to severe and affect each individual differently.

Not every person will experience all of the possible symptoms, and each reaction may be slightly different. However, common signs and symptoms include:

  • tingling in the mouth
  • burning sensation in the lips and mouth
  • facial swelling
  • a skin rash known as hives
  • wheezing
  • nausea or vomiting
  • diarrhea
  • a runny nose
  • streaming eyes

Symptoms of anaphylaxis

Anaphylaxis is a severe and systemic allergic reaction. It usually occurs soon after exposure to the specific allergen but can occasionally take a few hours to develop.

The signs and symptoms usually come on quickly and worsen rapidly. They may include:

  • a rapid fall in blood pressure
  • fear or a feeling of apprehension
  • an itchy, tickly throat
  • nausea
  • respiratory problems, such as wheezing or shortness of breath, which often become progressively worse
  • itchy skin, or a rash that may spread rapidly and cover much of the body
  • sneezing
  • streaming nose and eyes
  • a fast heartbeat, known as tachycardia
  • rapid swelling of the throat, lips, face, and mouth
  • vomiting
  • loss of consciousness

The most common allergenic foods account for about 90% of all food allergies, and people commonly refer to them as the “big eight allergens.” These foods are:

  • eggs
  • fish
  • milk
  • nuts from trees, including hazelnuts, walnuts, cashews, and pistachios
  • peanuts or groundnuts
  • shellfish, including shrimps, lobster, and crab
  • soybeans
  • wheat

The American College of Allergy, Asthma & Immunology say that the most common food allergens for children are milk, eggs, and peanuts.

They report that children generally outgrow allergies to milk, egg, soy, and wheat and that up to 25% of children may outgrow an allergy to peanuts.

European countries have additional top allergens that include sesame, celery, lupin (a legume), and mustard. Sesame is an increasingly common food allergy in the U.S.

Read more about common food allergies here.

To diagnose an allergy, the doctor will ask the person about their reactions to the food. They will want to know:

  • what symptoms occur
  • how long it takes for the reaction to begin
  • which foods cause it
  • whether the food is cooked
  • where the person eats it

The doctor will also be interested in any other existing allergies, such as seasonal allergies or asthma, and the person’s family history of allergies.

The following tests can help the doctor diagnose a food allergy:

  • Skin prick test: A healthcare professional places diluted foods onto the person’s arm and lightly pierces the skin. Any reaction, such as itching, swelling, or redness, indicates that the person may have an allergy. People may need to repeat this test several times.
  • Blood test: This test looks for the presence of antibodies that are specific to certain food proteins and can indicate an allergy.
  • Food diary: The person writes down everything they eat and describes symptoms if they occur.
  • Physician-supervised blinded oral food challenge: This is the most scientific method to diagnose a food allergy accurately. A physician gives the person a suspected food allergen in increasing amounts, monitoring for symptoms under close supervision. This method removes the chance of psychological reactions.

Experts have found that many people who think that they have a food allergy actually have a food intolerance, which is not the same.

If a person has a food allergy, their immune system overreacts to the food by producing antibodies called immunoglobulin E (IgE). The binding of these antibodies to the offending food allergen causes the symptoms of the allergic reaction.

IgE antibodies do not play a role in food intolerances, though other parts of the immune system may be involved.

The symptoms of food intolerances may be similar to those of food allergies, but they typically take longer to appear.

Unlike an allergy, which is only in response to a protein, a food intolerance can occur due to proteins, chemicals, or carbohydrates in foods. It can also sometimes be due to a lack of enzymes or compromised intestinal permeability.

In those with a food allergy, even a small amount of the particular food is likely to trigger the immune system, causing an allergic reaction. With food intolerances, an individual can typically eat small amounts of the food without it affecting them.

Celiac disease is an exception, as even a small amount of gluten can cause a reaction in those with this condition. There is immune system involvement in Celiac disease, but doctors consider it an autoimmune condition, not an allergy.

People often confuse the following conditions or issues for food allergies:

  • A lack of enzymes: The individual does not have any or enough of an enzyme necessary to digest a food properly. For example, those with lactose intolerance, which causes diarrhea, gas, cramping, and bloating, do not have enough of the enzyme lactase.
  • Irritable bowel syndrome (IBS): This long-term condition causes diarrhea, constipation, and stomach pains. People with IBS often have an intolerance to fermentable carbohydrates.
  • Food additive sensitivity: Triggers may include sulfites, which manufacturers use for preserving dried fruits or canned foods.
  • Psychological factors: Some people may feel ill just thinking about a particular food. The reasons for this are not always known.
  • Celiac disease: After eating gluten, those with this long-term autoimmune digestive condition may have diarrhea, stomach pain, and bloating, although many people are asymptomatic.

Read more about food allergy vs. food intolerance here.

In those with food allergies, the immune system treats a specific protein in a food as a harmful substance that may cause disease. It responds by producing IgE antibodies that will play a role in attacking this protein.

When the person eats the same food again, the antibodies are ready, so the immune system reacts immediately by releasing histamine and other chemical substances into the bloodstream. These chemicals cause the symptoms of food allergies.

Histamine causes blood vessels to expand and the skin to become inflamed or swollen. It also affects the nerves, making the skin feel itchy. The nose may produce more mucus, resulting in itching, burning, and a streaming nose.

Anyone can experience a food allergy, but some risk factors make it more likely to develop:

  • Family history: Food allergies can run in families. If close family members have asthma or any allergic diseases, including food allergies, eczema, and seasonal allergies, the person is more likely to develop food allergies.
  • Other allergic conditions: A child with one allergic condition often develops others, too. These conditions include food allergies, asthma, and seasonal allergies.
  • Early experiences: Research has shown that babies born by cesarean delivery may be more likely to develop food allergies. Introducing common allergens, such as peanuts, earlier in life can reduce the risk of food allergies developing.
  • Gut bacteria: Some research shows that people with nut or seasonal allergies have altered gut bacteria. Specifically, they have higher levels of Bacteroidales and lower levels of Clostridiales strains. Scientists are trying to determine whether influencing gut bacteria could help treat or prevent allergies.

Why do certain people have allergic reactions?

Food allergies appear to be on the rise. For instance, the Centers for Disease Control and Prevention (CDC) say that among children, “the prevalence of food allergies increased from 3.4% in 1997–1999 to 5.1% in 2009–2011.”

Researchers are not sure why numbers are increasing, but there are some theories:

  • Diet: Changes in eating habits in Western nations — such as a lower consumption of animal fats and higher intake of vegetable fats — may be the cause.
  • Antioxidants: Most people eat smaller quantities of fresh fruit and vegetables than previous generations did. These foods are high in antioxidants, which help protect against cell damage. Some research suggests that a lower antioxidant intake may be related to allergies.
  • Vitamin D: Food allergy prevalence is higher in countries further from the equator, where there is less sunlight, an important source of vitamin D. The suggestion is that low vitamin D intake may result in a higher food allergy risk.
  • Lack of early exposure: Also known as the hygiene hypothesis, this theory notes that many children are now growing up in sterile environments with much lower exposure to germs. Developed countries, in which people tend to have higher use of antibacterial products and less exposure to healthy bacteria in the environment, have significantly higher rates of food allergies.

However, all of the above are theories, with no compelling evidence to support them.

The traditional way to manage food allergies has been to avoid the food that causes the reaction. People can also treat the symptoms of a reaction when they arise.

Oral immunotherapy is a relatively new and investigative way to manage food allergies. It involves giving the person increasing amounts of an allergen to increase the threshold that triggers a reaction.

Oral immunotherapy is not available for all foods, but the Food and Drug Administration (FDA) have approved a treatment for peanut allergy, called Palforzia.

Elimination may involve not only not eating the particular food but also never inhaling it, touching it, or eating foods with traces of it inside. Cutlery, crockery, cooking surfaces, and chopping boards may also need to be free of the allergen.

When on an elimination diet, a person may need to look for other sources of certain nutrients. For instance, milk is a common source of calcium and protein, so people removing this from their diet will need to ensure that they get these nutrients from other foods.

People will need to read food and drink labels carefully. Even some soaps, pet foods, glues, and adhesives may have traces of a food allergen.

When eating out, being vigilant can be particularly difficult.

Medication for emergencies

The following medications are helpful in the event of an allergic reaction:

Antihistamines

These come in the form of gels, liquids, or tablets. They are usually effective for people with mild or moderate food allergy symptoms. Histamines are chemicals that cause most allergy symptoms, and antihistamines block their effects.

Epinephrine (adrenaline)

This treatment is for individuals who have food allergies that may result in anaphylaxis. Epinephrine keeps blood pressure up by constricting blood vessels. It also relaxes the airways.

People who have had severe allergic reactions should always carry an epinephrine auto-injector, such as an EpiPen, EpiPen Jr., Twinject, or Auvi-Q.

Food allergies are relatively common in the U.S., and their rates are increasing. They are most common in childhood, with many children outgrowing them before adulthood.

The most common food allergies in children include eggs, milk, and peanuts. The symptoms can range from mild to severe.

There has been no traditional cure for food allergies, but oral immunotherapy offers hope, and people can treat the symptoms when they arise. Avoiding products that contain the allergen allows people to prevent reactions from occurring.