Food allergies: Symptoms, treatments, and causes

People with a food allergy have an immune system that reacts to certain proteins found in food. Their immune system attacks these compounds as if it were a harmful pathogen, such as a bacterium or virus.

The National Institute of Allergy and Infectious Diseases estimates that about 5 percent of children and 4 percent of adults in America have a food allergy. This is a 20 percent increase in childhood food allergies in the last 20 years. Worldwide, food allergies affect 250 million to 550 million people in developed and developing countries.

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

Fast facts on food allergies

Here are some key points about food allergies. More detail and supporting information is in the main article.

Allergies in children appear to be increasing.

In some people, food allergies can be life-threatening.

Symptoms can include nausea, diarrhea, and streaming eyes.

Common triggers include eggs, nuts, soya, and milk.

Diagnosing food allergies can be challenging.

Symptoms of food allergy

Food allergies appear to be on the rise.
Food allergies appear to be on the rise.

Symptoms can range from mild to severe and affect each individual differently. Not every person will experience all of the below, and each reaction may be slightly different, but commons signs and symptoms include:

tingling in the mouth

burning sensation in the lips and mouth

lips and face might swell

skin rash

skin may become itchy and/or blotchy

wheezing

nausea

diarrhea

runny nose

streaming eyes

Symptoms of anaphylaxis

Anaphylaxis means a severe allergic reaction. It usually occurs soon after exposure to the specific allergen, but can take a few hours.

Signs and symptoms usually come on quickly and worsen rapidly; they may include:

a rapid fall in blood pressure

fear, a feeling of apprehension

itchy, tickly throat

nausea

respiratory problems, which often become progressively worse

skin is itchy, rash may spread rapidly and cover much of the body

sneezing

streaming nose and eyes

tachycardia (accelerated heartbeat)

throat, lips, face, and mouth swell rapidly

vomiting

loss of consciousness

Common food allergy triggers

According to the National Health Service, United Kingdom, among children, the most common foods to trigger allergic reactions are peanuts, wheat, soya, milk, and eggs.

In adults, they are types of fish, peanuts, some shellfish, such as lobster, crab, and prawns, tree nuts, such as pistachios, Brazil nuts, almonds, walnuts, and peanuts.

The most common allergenic foods, which account for about 90 percent of all food allergies, commonly referred to as the “big eight,” are:

eggs

fish

milk

nuts from trees (including hazelnuts, walnuts, almonds, and Brazil nuts)

peanuts (groundnuts)

shellfish (including shrimps, mussels, and crab)

soya

wheat

European countries have additional top allergens that include sesame, celery, lupin (a legume), and mustard.

A summary of these common food allergies is available here.

Skin prick test
A skin prick test can help diagnose a food allergy.

The doctor will ask the patient about their reaction, including the symptoms, how long it takes for a reaction to occur, which foods cause it, whether the food is cooked or not, and where it was eaten.

The doctor will be interested in any other existing allergies, such as hay fever or asthma.

The patient will also need to tell the doctor about close relatives who might have allergies.

Skin prick test – diluted foods are placed on the patient’s arm, and then the skin is pierced, introducing the food into the system. If there is any reaction, such as itching, swelling, or redness, it is likely there is some kind of allergy.

Skin prick testing can sometimes produce false-negative or false-positive results. Doctors usually order other tests to be sure.

Blood test – a patient’s blood is drawn to check for IgE antibodies that are specific to certain food proteins.

Elimination diet – suspected foods are not eaten for 4-6 weeks, typically, to see whether symptoms clear up. They are then reintroduced to see whether symptoms return.

Elimination diets should be supervised by a doctor or dietitian. It is important not to exclude major groups of foods indefinitely. Elimination diets are often considered the gold standard for identifying problem foods since many diagnostic tests can produce false results.

Food diary – patients write down everything they eat and describe symptoms if they occur.

Physician-supervised blinded oral food challenge – this is more accurate. The patient is given several different foods. One of them has tiny amounts of the suspected allergen. The patient eats each one, and their reaction is observed closely.

Blinded means the patient does not know which food has the suspected allergen; this is important because some people react psychologically to some foods (this would not be classed an allergy).

This type of test should only be done by a doctor at a suitable medical facility.

Allergy vs. intolerance

Experts have found that many people who think they have a food allergy actually have a food intolerance, which is not the same. Food intolerances do not involve IgE antibodies, though other parts of the immune system may be involved.

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