Food allergy

Causes

Many people have what is called a food intolerance. This term 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 (See: Lactose intolerance)
• Wheat and other grains that contain gluten (See: Celiac disease)

A true food allergy is much less common.

• Normally, your body's immune system defends against possibly harmful substances, such as bacteria, viruses, and toxins.
• In some people, this immune response is triggered by a certain food.
• When this occurs, the immune system releases substances that cause the symptoms of food allergies.

Any food can cause an allergic reaction, but a few foods are the main culprits. The most common food allergies are to:

• Eggs (mostly in children)
• Fish (older children and adults)
• Milk (mostly in children)
• 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 (mostly in children)

Food additives -- such as dyes, thickeners, and preservatives -- may rarely cause a food allergy or intolerance reaction.

Some people have an allergy 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. Rarely, the symptoms may begin hours after eating the food.

If you develop symptoms shortly after eating a certain food, you may have a food allergy. Key symptoms of a food allergy include hives, a hoarse voice, and wheezing.

Other symptoms that may occur include:

• Abdominal pain
• Diarrhea
• Difficulty swallowing
• Itching of the mouth, throat, eyes, skin, or any other area
• Light-headedness or fainting
• Nasal congestion
• Nausea
• Runny nose
• Swelling (angioedema), especially of the eyelids, face, lips, and tongue
• Shortness of breath
• Stomach cramps
• Vomiting

Symptoms of mouth (oral) allergy syndrome:

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

Exams and Tests

In severe reactions, you may have low blood pressure and blocked airways.

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 health care 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 health care provider -- especially if your first reaction was severe.

Treatment

The only proven treatment for a food allergy is to avoid the food. 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 health care provider may suggest trying a soy-based formula or something called an elemental formula, if it is available.

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

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 can also provide some relief.

Talk to your health care provider if you think you have had an allergic reaction to food, even if it is only a local reaction.

Anyone who has been diagnosed with a food allergy should carry (and know how to use) injectable epinephrine 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 Anaphylaxis Network -- www.foodallergy.org

Outlook (Prognosis)

Many children will outgrow their allergy to milk, egg, 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.

Avoiding the offending foods may be easy if the food is uncommon or easy to identify. However, you may need to severely restrict your diet, carefully read all package ingredients, and ask detailed questions when eating away from home.

Possible Complications

Anaphylaxis is a severe, whole-body allergic reaction that is life threatening. Although people with oral allergy syndrome rarely have an anaphylactic reaction, they should ask their doctor whether 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 evaluated by an allergy specialist.

Prevention

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

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

Alternative Names

Allergy to food

References

Lack G. Clinical practice. Food allergy. N Engl J Med. 2008;359:1252-1260.

Chafen JJ, Newberry SJ, Riedl MA, et al. Diagnosing and managing common food allergies: a systematic review. JAMA. 2010 May 12;303(18):1848-56.

Update Date: 8/2/2012

Updated by: Stuart I. Henochowicz, MD, FACP, Associate Clinical Professor of Medicine, Division of Allergy, Immunology, And Rheumatology, Georgetown Unviersity Medical School. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.