Learning About Food Allergies

Who has food allergies?

Food allergies are an increasingly common problem all over the world. As many as 6% to 8% of children in the United States may be food allergic. While many allergies are outgrown, those to certain foods including peanuts and shellfish tend to persist into adulthood. Three to 4% of adults have food allergies. The numbers of allergic individuals are continuing to rise.

In the United States, some 2.5% of babies are allergic to cow’s milk, 1.6% are allergic to eggs, and between 0.8% and 1.5% are allergic to peanuts. Children can also be allergic to tree nuts, soy, fish, wheat, shellfish, and wheat. In many European countries, children are often allergic to vegetables like carrots and fruit such as kiwi and peach. Sesame seeds can also cause food allergies.

Most people who have food allergies also have other allergy-based diseases. In children, this can be eczema, a red and itchy rash that is often difficult to treat. Adults and children with food allergies can have asthma as well as hay fever. All of these disorders run in families.

Although many allergies disappear with age, during the period when the allergy is occurring, it tends to get worse with each exposure to the specific food.

Symptoms of food allergy

If you have had a true allergic reaction to food, you probably know, and it might have been very frightening. With most food allergies, your body makes a kind of antibody called IgE which causes a cascade of chemical reactions when it interacts with parts of the food, usually the proteins. These chemicals, which include histamine, cause itching, redness and swelling, sometimes in a small area but at other times affecting the entire body.

When you are mildly allergic to some foods, especially certain fruits, you can develop what is called the oral allergy syndrome. This causes redness and itching around the mouth.

Food allergies can also cause hives, which are itchy, raised bumps which look somewhat similar to mosquito bites, around the mouth or all over the body.

Severe food allergies can cause swelling in the mouth, the face, the throat, and the respiratory tract. This can impede breathing, by closing up the windpipe and/or triggering asthma. People experiencing difficulty breathing due to food allergies can have noisy, labored breathing.

Food allergies can cause vomiting, diarrhea and abdominal pain.

When the whole body is affected, the reaction is called anaphylaxis. This will include trouble breathing, gastrointestinal symptoms, and eventually a drop in blood pressure which can lead to death. This is also called anaphylactic shock. Most but not anaphylactic reactions are due to food allergies.

In the United States, there are as many as 120,000 patients with anaphylactic reactions a year seen in emergency rooms. As many as 3,000 people wind up in the hospital. Between 0.5% and 2% of these reactions are fatal.

As frightening as anaphylaxis is, it is still very rare. It does not usually happen with milk, egg or wheat allergies. It is more common with peanut, tree nut, and shellfish allergies.

Many people who believe they have food allergies are not really allergic, but have reactions to irritating ingredients. For example spicy foods can cause heartburn. Some people react to food or drink additives like sulfites. Others may have diarrhea, gas and cramps from dairy products. This is from lactose intolerance and not food allergy. Lactose intolerance is very common, and it occurs because many adults do not have enough of the enzyme that breaks down lactase, or milk sugar.

The diagnosis of food allergies

Food allergies can be difficult to diagnose in some cases. Especially with children, it is important to correctly identify the foods and not restrict their diet more than is needed.

The diagnosis can be suspected from a patient’s history, if reactions are consistent to certain foods and they are reproducible, occurring between 20 minutes and 2 hours after eating the food. Some children may be allergic to only one food; others are allergic to multiple foods that are dietary mainstays, like milk, eggs, and wheat. Some of these children are also allergic to soy, making a source of formula or calcium and protein-containing drinks difficult to find.

If food allergy is suspected, a primary care doctor like a pediatrician, family practitioner or internist may begin the evaluation. Unless symptoms are extremely mild, an allergist should be involved in the diagnosis and treatment of food allergies.

Skin prick testing (SPT) can be done to help diagnose food allergies. These tests are done by introducing tiny amounts of the allergic parts of common foods (called allergens) underneath the skin. A skin reaction is noted and measured. The larger the reaction, the more likely it is that a person is allergic to that substance. Skin tests may help pinpoint allergies, but are never completely accurate. SPTs are not done when someone has had a severe reaction.

Blood tests can also measure the amount of antibodies (IgE) in the blood to specific foods. This may be safer and more tolerable for people with strong reactions. There are specific cut-off values of IgE amounts, above which allergy is extremely likely. However, the blood tests are also not 100% accurate. There is research into finding out which specific, tiny parts of a food usually cause allergic reactions, and also research into testing for antibodies to those specific pieces. The results of these studies may be more accurate tests.

When a child or adult’s history suggests food allergies, the information from skin tests or blood tests may help narrow down the possible foods.

If a specific food is suspected as an allergic trigger, but the reaction is not severe, simply eliminating the food should help confirm the allergy. Symptoms should go away while the food is not eaten, and return when it is added back into the diet. However, anyone who has had a severe reaction or anaphylaxis from a specific food should not try eating it again.

The “gold standard” test for food allergy is a double-blind, placebo-controlled, oral food challenge. This means that a person with allergies will be given small amounts of the food under suspicion in a doctor’s office or even hospital. Only tiny amounts are used to begin with. Double blind means that neither the doctor nor the patient know what food the patient is being given. Placebo controlled means that foods not under suspicion are also given. If there is no reaction, larger doses may be used. Open challenges are often done instead, when everyone knows what the person is eating.

In all cases of oral food challenges, the medical staff must be ready to treat a severe reaction. However, patients who have had severe reactions in the past should not be given oral challenges.

Treatment of food allergies

Once the diagnosis is made, the only way to handle food allergies is to avoid the foods known to cause them. Treatment for mild allergies like the oral allergy syndrome can include antihistamines like Benadryl®.

People who have had any serious reaction to foods need to have an Epipen®, which is an epinephrine (also known as adrenaline) autoinjector. They need to carry the autoinjector at all times and know how to use it. With any suspected exposure, they must inject themselves immediately. People who die from anaphylaxis are usually those with known food allergies who delay using the Epipen or don’t use it at all. It is critical that every seriously allergic person, their families and anyone taking care of allergic children learn how to use an Epipen.

The minute a person with a history of anaphylaxis believes they may have eaten a food they are allergic to, they need to use their Epipen and call 911. Further treatment is frequently necessary. Sometimes the reactions are biphasic, meaning that symptoms start to improve and then worsen again. More than one injection of adrenaline may be necessary, as well as fluids, corticosteroids, and different types of antihistamines.

Hidden dangers: Food contamination

Foods are not always properly labeled. Anything bought in a store or restaurant can be contaminated with an allergen that is not supposed to be in the product. The FDA has initiated guidelines for correct labeling of products, but they are not always followed.

Anything that is baked in a bakery that uses nuts can be contaminated by nut residue on the machinery. The same is true for wheat, eggs, milk, and virtually anything else. Since children tend to outgrow many of these allergies, and severe reactions to eggs and milk are rare, the greatest danger tends to be with peanuts, tree nuts, and shellfish.

Allergic individuals need to discuss their diet with their allergist. Children especially may need a dietician to help make sure they get enough nutrition. Allergic people need to talk to their doctors about food labels. Some companies selling baked goods have chosen labels that say they could have been contaminated just for legal protection.

Accidental exposure can also occur at school when children eating peanut butter sandwiches leave behind enough to make a peanut-allergic child sick, or when parents bring cupcakes to school and an the teacher and parent do not think to prevent an allergic child from eating something they are allergic to. This is something that can be very difficult and stressful for children.

Adults with food allergies also need to be very careful. Certain cuisines commonly contain certain allergens like peanuts. Others use fish and shellfish. Adults have to learn where it is the safest to eat out.

Help with all of this can be found at the Food Allergy Network (http://www.foodallergy.org/). This is an invaluable resource for parents of children with food allergy as well as allergic adults.

The future of food allergy treatment

The treatment of food allergies in the future may be different. There is work being done to desensitize people to their food allergen, so that if they are accidentally exposed they will not have a potentially deadly reaction. Peanuts are being tested in this way, as is milk. Foods are given in extremely tiny amounts, either orally or under the tongue. The danger is of provoking a serious reaction. The hope is that people can learn to tolerate increasing doses of the food in question, up to the point that they can tolerate the amount that they might accidentally eat.

Other work includes trying to use foods that have been heated or baked to try and make people tolerant of those antigens.

There is ongoing research looking for drugs that can prevent or stop food allergies. One class of drug being evaluated blocks IgE. There is also a Chinese herbal medicine in early stages of testing.

For now, accurate diagnosis and avoidance of the foods causing allergy is the only safe way to handle food allergies.


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Clark, A.T. et al. Successful oral tolerance induction in severe peanut allergy. Allergy. 2009;64:1218-20.

Lack, Gideon. Food Allergy. New England Journal of Medicine 2008;359:1252-60.

Pereira, C, Bartolome, B, Asturias, JA, et al. Specific sublingual immunotherapy with peach LTP (Pru p 3). One year treatment: a case report. Cases Journal. 2009;2:6553.

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Dr. Anna Kaplan

Dr. Anna Kaplan graduated with a BA in English literature from Pomona College in 1975. She received her MD from U.S.C. School of Medicine in 1979. A three-year residency (training period) in family practice followed, and she was certified by the American Board of Family Physicians in 1982. She recertified, a normal procedure, in 1988 and 1995. She retired from active practice after 15 years, but keeps up with medicine via continuing medical education.

Dr. Kaplan has written in the medical field for both consumers as well as professionals. She has also authored hundreds of articles on other subjects.

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