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Food allergy

Definition

A food allergy is type of immune response triggered by eggs, peanuts, milk, shellfish or some other specific food.

Test Your Food Allergy Knowledge

What are common symptoms of food allergies?

Answer:

The correct answer is all of the above. Eating something you're allergic to can trigger symptoms ranging from a runny nose to a dangerous full-body reaction. Talk to your doctor if you have any of these symptoms after eating a food, even if it's a small reaction.
Food allergy and food intolerance are the same.

Answer:

The correct answer is false. A food allergy occurs when your immune system overreacts to a food and releases the chemical histamine. This causes allergic symptoms. Food intolerance is more common and doesn't involve your immune system. Sometimes it occurs because you can't digest part of a food, such as lactose, a type of sugar in milk.
Which is a common food allergy?

Answer:

The correct answer is all of the above. Any food can cause an allergic reaction, but these are the most common. Other common foods include shellfish, soy, and tree nuts.
If you eat something you're allergic to, your body will react within:

Answer:

The correct answer is two hours. Rarely, the symptoms may begin several hours after eating the food. Mild symptoms, such as a hive on your chin after eating something, will disappear soon and do not require treatment. However, you should tell your doctor about it.
For some people, food allergies can be life-threatening.

Answer:

The correct answer is true. Some people have a severe allergic reaction, called anaphylaxis. This causes a whole-body reaction. Symptoms can start within minutes and may include breathing and swallowing problems, slurred speech, or passing out. If you have any of these symptoms, call 9-1-1 right away.
The only proven treatment for a food allergy is to avoid the food.

Answer:

The correct answer is true. If you're allergic to a food, the best way to prevent a reaction is to cut the food from your diet. Other treatments, such as allergy shots and probiotics, don't work to treat food allergies.
Many children outgrow their allergy to:

Answer:

The correct answer is eggs. Many children will outgrow their allergy to eggs, milk, wheat, and soy by the time they are 5 years old if they avoid that food when they are young. Allergies to peanuts, tree nuts, and shellfish tend to last a lifetime.
To find out if you're still allergic to a food, you should eat a small amount.

Answer:

The correct answer is false. Do not eat a food that caused a reaction in the past without checking with your doctor first. A mild reaction in the past can become a more severe reaction the second or third time you try a food. Your doctor may want to be present when you try the food.
People with food allergies should always carry epinephrine.

Answer:

The correct answer is true. Epinephrine is a medicine you can carry with you. It can stop a severe allergic reaction and save your life. It comes in a small syringe that is ready for you to give yourself a shot. If you've had an allergic reaction to food -- even a mild reaction -- talk to your doctor about this medicine.
If you begin wheezing after eating a food, you should:

Answer:

The correct answer is to inject epinephrine and then call 9-1-1. Make sure you know how to use it. Also show loved ones how to use it in case you can't inject yourself.
Fresh fruits are a common cause of mouth allergies.

Answer:

The correct answer is true. If you have an allergy to fruit, melons, apples, pineapple, and other fruits can cause your lips, tongue and throat to itch – especially if you eat them raw. The more fruit you eat, the more severe the reaction. A more severe reaction is rare.
Which of the following may prevent food allergies in children?

Answer:

The correct answer is breastfeeding. Waiting to add allergy-causing foods until your baby is a little older also may help. The timing for this varies from food to food and from baby to baby. Ask your child’s health care provider when is best to start certain foods that commonly cause allergic reactions.

Alternative Names

Allergy to food; Food allergy - peanuts; Food allergy - soy; Food allergy - fish; Food allergy - shellfish; Food allergy - eggs; Food allergy - milk

Causes

Many people have a food intolerance. This term usually refers to heartburn, cramps, belly pain, or diarrhea that can occur after they eat foods such as:

  • Corn products
  • Cow's milk and dairy products (lactose intolerance)
  • Wheat and other grains that contain gluten (celiac disease)

A true food allergy is much less common.

The immune system normally protects the body against harmful substances, such as bacteria and viruses. It also reacts to foreign substances called allergens. These are usually harmless, and in most people, do not cause a problem.

Hives (urticaria) - close-up
Hives develop when histamine is released into the small blood vessels (capillaries). The capillaries dilate which causes a welt, and fluid oozes into the surrounding tissue, causing swelling. Histamine also causes intense itching.

In a person with a food allergy, the immune response is oversensitive. When it recognizes an allergen, the immune system launches a response. Chemicals such as histamines are released. These chemicals cause allergy symptoms.

Any food can cause an allergic reaction. The most common food allergies are to:

  • Eggs (mostly in children)
  • Fish (older children and adults)
  • Milk (people of all ages)
  • Peanuts (people of all ages)
  • Shellfish such as shrimp, crab, and lobster (people of all ages)
  • Soy (mostly in children)
  • Tree nuts (people of all ages)
  • Wheat (people of all ages)

In rare cases, food additives, such as dyes, thickeners, and preservatives can cause a food allergy or intolerance reaction.

Some people have an oral allergy. This is an allergy type syndrome that affects the mouth and tongue after they eat certain fresh fruits and vegetables:

  • Melons, apples, pineapple, and other foods contain substances that are similar to certain pollens.
  • The reaction most often occurs when you eat the raw form of the foods. How severe the reaction is depends on how much of the food you eat.

Symptoms

Symptoms usually begin within 2 hours after eating. Sometimes, the symptoms begin hours after eating the food.

Key symptoms of a food allergy include hives, a hoarse voice, and wheezing.

Other symptoms that may occur include:

  • Swelling (angioedema), especially of the eyelids, face, lips, and tongue
  • Trouble swallowing or breathing due to swelling in the throat
  • Itching of the mouth, throat, eyes, skin, or any other area
  • Lightheadedness or fainting
  • Nasal congestion, runny nose
  • Stomach cramps, diarrhea, nausea, or vomiting
Perioral dermatitis
Perioral dermatitis is most common in young to middle age women. Frequently, no specific cause is found. However, there appears to be an association with fluorinated steroids. In children, dermatitis around the mouth may be associated with irritation from specific foods or other materials carried to the face on the hands.

Symptoms of mouth (oral) allergy syndrome:

  • Itchy lips, tongue, and throat
  • Swollen lips (sometimes)

In a severe reaction, called anaphylaxis, in addition to the above symptoms, you may have low blood pressure and blocked airways. This can be life threatening.

Exams and Tests

Blood or skin tests are sometimes used to confirm that you have an allergy. A double-blind food challenge is one way to diagnose true food allergies. During this test, you and your health care provider will not know what you are eating.

With elimination diets, you avoid the suspected food until your symptoms disappear. Then you start eating the foods again to see if you develop an allergic reaction.

In provocation (challenge) testing, you eat a small amount of the suspected food under medical supervision. This type of test may cause severe allergic reactions. Challenge testing should only be done by a trained provider.

Never try to cause a reaction or reintroduce a food on your own. These tests should only be done under the guidance of a provider, especially if your first reaction was severe.

Patient Education Video: Allergy testing

Treatment

If you suspect that you or your child has a food allergy, see an allergy specialist doctor (allergist).

Treatment may involve any of the following:

  • Avoiding the food (this is the most effective treatment).
  • Desensitization, during which you eat a small amount of the food each day. This must be done under an allergist's guidance.

Other treatments, including allergy shots and probiotics, have not been proven to help with food allergies.

If your child has a problem with cow's milk formula, your provider may suggest trying a soy-based formula or something called an elemental formula, if it is available.

If you have symptoms on only one area of the body, for example, a hive on the chin after eating the food, you may not need any treatment. The symptoms will likely go away in a brief time. Antihistamines may relieve the discomfort. Soothing skin creams may also provide some relief.

If you have been diagnosed with a food allergy, learn how to use injectable epinephrine. You should have it with you at all times. If you develop any type of serious or whole-body reaction (even hives) after eating the food:

  • Inject the epinephrine.
  • Then go to the nearest hospital or emergency facility right away, preferably by ambulance.

Support Groups

The following groups can provide more information about food allergies:

Outlook (Prognosis)

Allergies to peanuts, tree nuts, and shellfish tend to last a lifetime.

Simple carbohydrates
Simple carbohydrates are broken down quickly by the body to be used as energy. Simple carbohydrates are found naturally in foods such as fruits, milk, and milk products. They are also found in processed and refined sugars such as candy, table sugar, syrups, and soft drinks. The majority of carbohydrate intake should come from complex carbohydrates (starches) and naturally occurring sugars rather than processed or refined sugars.

Avoiding the problem foods may be easy if the food is uncommon or easy to identify. When eating away from home, ask detailed questions about the food you are served. When buying food, read package ingredients carefully.

Possible Complications

Shock
Shock is a severe condition that occurs when not enough blood flows through the body, causing very low blood pressure, a lack of urine, and cell and tissue damage.

Anaphylaxis is a severe, whole-body allergic reaction that is life threatening. Although people with oral allergy syndrome may have an anaphylactic reaction in rare cases, they should ask their doctor if they need to carry injectable epinephrine.

Food allergies can trigger or worsen asthma, eczema, or other disorders.

When to Contact a Medical Professional

Steps to take when a food allergy reaction occurs:

  • Call your local emergency number, such as 911, if you have any serious or whole-body reactions, particularly wheezing or difficulty breathing, after eating a food.
  • If your provider prescribed epinephrine for severe reactions, inject it as soon as possible, even before calling 911. The sooner you inject the epinephrine, the better.
  • Anyone who has had an allergic reaction to a food should be seen by an allergist.

Prevention

Breastfeeding may help prevent allergies. Otherwise, there is no known way to prevent food allergies.

A common belief and practice is to delay introducing allergy-causing foods to infants until their gastrointestinal tract has had a chance to mature. The timing for this varies from food to food and from baby to baby.

Avoiding peanuts in early childhood does not appear to prevent, and may even enhance, the development of peanut allergy. Doctors now suggest introducing peanut-containing foods to infants, which may prevent peanut allergy. Talk to your child's provider to learn more.

Once an allergy has developed, carefully avoiding the offending food usually prevents further problems.

Gallery

Simple carbohydrates
Simple carbohydrates are broken down quickly by the body to be used as energy. Simple carbohydrates are found naturally in foods such as fruits, milk, and milk products. They are also found in processed and refined sugars such as candy, table sugar, syrups, and soft drinks. The majority of carbohydrate intake should come from complex carbohydrates (starches) and naturally occurring sugars rather than processed or refined sugars.
Shock
Shock is a severe condition that occurs when not enough blood flows through the body, causing very low blood pressure, a lack of urine, and cell and tissue damage.
Hives (urticaria) - close-up
Hives develop when histamine is released into the small blood vessels (capillaries). The capillaries dilate which causes a welt, and fluid oozes into the surrounding tissue, causing swelling. Histamine also causes intense itching.
Simple carbohydrates
Simple carbohydrates are broken down quickly by the body to be used as energy. Simple carbohydrates are found naturally in foods such as fruits, milk, and milk products. They are also found in processed and refined sugars such as candy, table sugar, syrups, and soft drinks. The majority of carbohydrate intake should come from complex carbohydrates (starches) and naturally occurring sugars rather than processed or refined sugars.
Stomach
The stomach is the portion of the digestive system most responsible for breaking down food. The lower esophageal sphincter at the top of the stomach regulates food passing from the esophagus into the stomach, and prevents the contents of the stomach from reentering the esophagus. The pyloric sphincter at the bottom of the stomach governs the passage of food out of the stomach into the small intestine.

References

Bird JA, Jones S, Burks W. Food allergy. In: Rich RR, Fleisher TA, Shearer WT, Schroeder HW, Frew AJ, Weyand CM, eds. Clinical Immunology: Principles and Practice. 5th ed. Philadelphia, PA: Elsevier; 2019:chap 45.

Sicherer SH, Lack G, Jones SM. Food allergy management. In: Burks AW, Holgate ST, O'Hehir RE, et al, eds. Middleton's Allergy: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 82.

Togias A, Cooper SF, Acebal ML, et al. Addendum guidelines for the prevention of peanut allergy in the United States: report of the National Institute of Allergy and Infectious Diseases-sponsored expert panel. J Allergy Clin Immunol. 2017;139(1):29-44. PMID: 28065278 pubmed.ncbi.nlm.nih.gov/28065278/.

Last reviewed October 11, 2020 by David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team..

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