Food Allergies

About Food Allergies

With a food allergy, the body reacts as though that particular food product is harmful. As a result, the body's immune system (which fights infection and disease) creates antibodies to fight the food allergen, the substance in the food that triggers the allergy.

The next time a person comes in contact with that food by touching or eating it or inhaling its particles, the body releases chemicals, including one called histamine, to "protect" itself. These chemicals trigger allergic symptoms that can affect the respiratory system, gastrointestinal tract, skin, or cardiovascular system. These symptoms might include a runny nose; an itchy skin rash; a tingling in the tongue, lips, or throat; swelling; abdominal pain; or wheezing.

People often confuse food allergies with food intolerance because of similar symptoms. The symptoms of food intolerance can include burping, indigestion, gas, loose stools, headaches, nervousness, or a feeling of being "flushed." But food intolerance:

• doesn't involve the immune system
• can be caused by a person's inability to digest certain substances, such as lactose
• can be unpleasant but is rarely dangerous

According to the U.S. Food and Drug Administration (FDA), up to 6% of children in the United States under age 3 have food allergies. They are less common in adults but, overall, food allergies affect nearly 11 million people in the United States.

Common Food Allergens

A child could be allergic to any food, but these eight common allergens account for 90% of all reactions in kids:

1. milk
2. eggs
3. peanuts
4. soy
5. wheat
6. tree nuts (such as walnuts and cashews)
7. fish
8. shellfish (such as shrimp)

In general, most kids with food allergies outgrow them. Of those who are allergic to milk, about 80% will eventually outgrow the allergy. About two-thirds with allergies to eggs and about 80% with a wheat or soy allergy will outgrow those by the time they're 5 years old.

Other food allergies are harder to outgrow. Only about 20% of people with allergies to peanuts and about 10% of those allergic to tree nuts outgrow the allergies. Fish and shellfish allergies usually develop later in life and are even more rarely outgrown.

Food Allergy Reactions

Food allergy reactions can vary from person to person. Some can be very mild and only involve one part of the body, like hives on the skin. Others can be more severe and involve more than one part of the body. Reactions can occur within a few minutes or up to a few hours after contact with the food.

Food allergy reactions can affect any of the four following areas of the body:

1. skin: itchy red bumps (hives); eczema; redness and swelling of the face or extremities; itching and swelling of the lips, tongue, or mouth (skin reactions are the most common type of reaction)
2. gastrointestinal tract: abdominal pain, nausea, vomiting, or diarrhea
3. respiratory tract: runny or stuffy nose, sneezing, coughing, wheezing, shortness of breath
4. cardiovascular system: lightheadedness or fainting

A serious allergic reaction with widespread effects on the body is known as anaphylaxis. This sudden, potentially life-threatening allergic reaction involves two or more of the body areas listed above. In addition, there also can be swelling of the airway, serious difficulty with breathing, a drop in blood pressure, loss of consciousness, and in some cases, even death.

Diagnosing a Food Allergy

If you suspect that your child might have a food allergy, contact your doctor. To diagnose an allergy, the doctor will likely ask about:

• your child's symptoms
• how often the reaction occurs
• the time it takes between eating a particular food and the start of the first symptoms
• whether any family members have allergies or conditions like eczema and asthma

The doctor will look for any other conditions that could cause the symptoms. For example, if your child seems to have diarrhea after drinking milk, the doctor may check to see if lactose intolerance could be the cause rather than a food allergy. Celiac disease — a condition in which a person cannot tolerate gluten, a protein found in wheat and certain other grains — also can mimic the symptoms of food allergies.

If the doctor suspects a food allergy, you'll likely be referred to an allergy specialist, who will ask more questions, perform a physical exam, and probably perform tests to help make a diagnosis.

One of those tests might be a skin test. The test involves placing liquid extracts of food allergens on your child's forearm or back, pricking the skin, and waiting to see if reddish raised spots (called wheals) form within 15 minutes. A positive test to a certain food only shows that your child might be allergic to that food — the allergist may do additional tests for confirmation.

The allergy specialist might also perform blood tests, called RASTs (radioallergosorbent tests), which check the blood for IgE antibodies to specific foods. The results show the concentration of IgE in the blood. For several foods, different cutoffs indicate a high likelihood of an allergy. If someone has both a positive skin test and and a RAST above the cutoff, an allergy to that food is diagnosed and no further testing is needed.

If the test results are still unclear, the allergist may perform a food challenge. (More often, though, this test is done to determine if someone has outgrown a certain allergy.) During this test, a person might be given gradually increasing amounts of the potential food allergen to eat while being watched for symptoms by the doctor. The test should only be performed in an allergist's office or hospital that has access to immediate medical care and medications because a life-threatening reaction could occur.

Treating a Food Allergy

After diagnosing your child with a food allergy, the allergist will help you create a treatment plan. No medication can cure food allergies, so treatment usually means avoiding the allergen and all the foods that contain it.

You'll need to familiarize yourself with food labels so you can avoid the allergen. Since 2006, a new food labeling law has made this a little easier. Makers of packaged foods are required to clearly state, in or near the ingredient lists, whether the product contains milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, or soy.

Although there's no cure for food allergies, medications can treat both minor and severe symptoms. Antihistamines might be used to treat symptoms such as hives, runny nose, or abdominal pain associated with an allergic reaction.

If your child wheezes or has asthma flares (also called attacks) as the result of a food allergy, the doctor will likely recommend that a bronchodilator such as albuterol (which can be inhaled from a handheld pump device) be taken right away to reduce breathing difficulties.

But remember: If your child experiences an allergy-triggered asthma attack, it's important to consider also giving epinephrine and seek emergency medical treatment immediately in case the asthma symptoms are part of anaphylaxis.

Epinephrine is often used to treat severe allergic reactions, or anaphylaxis. If your child has severe food allergies, your allergist will want you to have two epinephrine autoinjectors (commonly called EpiPens) on hand at all times in case of a life-threatening reaction. This will mean keeping epinephrine in your home, briefcase or purse, and also at relatives' homes and your child's day care or school.

Signs and symptoms of anaphylaxis that would require epinephrine include:

• hoarseness
• sensation of tightness in the throat
• difficulty breathing
• any symptoms from two or more of the body systems, such as hives and abdominal pain, or any other combination of two or more symptoms that affect different parts of the body

After your child receives epinephrine, you should go immediately to a hospital emergency room so additional treatment can be given, if needed. Also, they'll observe your child for at least 4 hours to watch for signs of a second wave of symptoms (called a biphasic reaction), which occurs in many cases.

You and your child's allergist should work together to develop a written food allergy emergency action plan to give to the school, childcare provider, and any other caregivers.

Reviewed by: Steven Dowshen, MD
Date reviewed: January 2012
Originally reviewed by: Stephen J. McGeady, MD