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Food allergy

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

Causes

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

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.

Food allergies

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
Dermatitis, perioral

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.

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 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.

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

Food Allergy and Research and Education (FARE) -- www.foodallergy.org

Outlook (Prognosis)

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

Read food labels

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

Anaphylaxis

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

  • 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 doctor 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 don't know whether it is effective to introduce foods that commonly cause allergies in breastfed or other children to prevent future food allergies. Always discuss this with your child's provider.

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

Alternative Names

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

References

Bohle B. Food allergy. In: Rich RR, Fleisher TA, Shearer WT, Schroeder HW Jr, Frew AJ, Weyand CM, eds. Clinical Immunology. 4th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 43.

Du Toit G, Sayre PH, Roberts G, et al; Immune Tolerance Network LEAP-On Study Team. Effect of avoidance on peanut allergy after early peanut consumption. N Engl J Med. 2016;374(15):1435-1443. PMID: 26942922 www.ncbi.nlm.nih.gov/pubmed/26942922.

NIAID-sponsored expert panel, Boyce JA, Assa'ad A, et al. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel. J Allergy Clin Immunol. 2010;126(6 Suppl):S1-S58. PMID: 21134576 www.ncbi.nlm.nih.gov/pubmed/21134576.

Sicherer SH, Lack G, Jones SM. Food allergy management. In: Adkinson NF Jr, Bochner BS, Burks AW, et al, eds. Middleton's Allergy: Principles and Practice. 8th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 84.

Review Date 10/1/2016

Updated by: Stuart I. Henochowicz, MD, FACP, Associate Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School, Washington, DC. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.