Food Allergy

Adverse Reactions to Foods - A Patient's Guide
Hippocrates, the "father of medicine," was one of the first to note that cow's milk could cause health problems for some people. Although we don't know if he was referring to a true allergy to cow's milk protein or to an inability to digest a milk sugar called lactose. We do know that food allergy reports began to appear in Europe in the early 1900s. Since the 1940s, food allergy has been recognized by doctors around the world.

The true number of people who have food allergy is unknown. Incidence is higher in infants than in adults. However, many adverse reactions to foods, such as cow's milk, are seldom a result of true allergic reactions. In some cases, symptoms have been presumed to be allergic reactions only because no other cause could be found and/or because the patient's symptoms improved when the food was removed from the diet.

What do we mean by the term "food allergy?" Here are some common terms that may help you understand this condition:

Adverse reaction: any abnormal reaction to a food or food additive, whether caused by allergic or non- allergic mechanisms.

Food allergy, hypersensitivity or sensitivity: an immunologic reaction that involves the body's immune system overreacting to ordinarily harmless substances. This also refers to irritating or uncomfortable symptoms that may result after eating a food or food additive. The word "allergy" is frequently overused and misused; the reaction only occurs in some people, and usually occurs after just a small amount of the food or food additive is ingested. An example of this is wheezing after consuming dairy products.

Food intolerance: a physical response to a food or food additive. This response is not necessarily immunologic, e.g., milk-sugar (lactose) intolerance, which occurs when an individual lacks the enzymes to break down the milk sugar for proper digestion.

Food anaphylaxis: a severe allergic reaction that can sometimes be fatal.

Food poisoning: an adverse reaction that does not involve immune system mechanisms. It can be caused by food that has been contaminated with toxins (poisons or bacteria), microorganisms or parasites.

Pharmacologic food reaction: an adverse reaction in which a chemical found in a food or food additive produces a drug-like (pharmacologic) effect, e.g., caffeine in coffee causing "the jitters."

Foods That May Cause Reactions
Food allergens, the parts of foods that cause allergic reactions, are usually proteins. Most of these allergens can still cause reactions even after they are cooked or have undergone digestion in the intestines. In studies of allergen content, cow's milk, eggs, peanuts, wheat, and soy have been found to be the most common food allergens. Other known food allergens include shrimp, codfish, soybeans, and crab.

In some food groups, especially legumes and seafoods, an allergy to one member of a family may result in the person being allergic to other members of the same group, known as cross-reactivity. People who are allergic to peanuts are more likely to be allergic to soybeans, peas, and other legumes than to walnuts or pecans. However, some may be allergic to both peanuts and walnuts. These allergies are called coincidental allergies.

Within animal-based food families, cross-reactivity is not seen as often. For example, people allergic to cow's milk can usually eat beef, and people allergic to eggs can usually eat chicken.

Cooking some proteins usually reduces their ability to cause a reaction, but not always. In fact, the heating process may actually make some proteins more allergenic. The protein of cow's milk is composed of two types: casein (80%,) and whey (20%). The allergenic potential of these proteins is not reduced by heating. Those allergic to eggs usually react only to the egg white, which contains several proteins. Again, cooking or heating does not make these proteins non-allergenic. Natural processes such as ripening also may affect the allergenic properties of a food; tomatoes become more allergenic as they ripen.

Food Intolerance Reactions
Food intolerance reactions are usually caused by factors in the diet other than proteins (food allergens). For instance, one common food intolerance reaction may be the result of the body's inability to properly digest sugars in the food, e.g., milk sugar intolerance. Other food intolerance reactions may be the result of natural drug-like chemicals in the foods, e.g., reactions to caffeine (jitteriness) in coffee or soft drinks, or reactions (headaches) to amines in cheese and chocolate. (Examples of the amine-type drugs include tyramine, found in cheese, and phenylethylamine, found in chocolate). Still other non-allergic adverse reactions may be due to chemicals added to food as preservatives or to increase its appeal. These chemicals are called food additives and their effects are discussed in Tip#13.

Severe Allergic Reactions Caused by Foods
Anaphylaxis is a general allergic reaction that is often severe and sometimes fatal. This reaction may involve any body system; however, the skin, nose, throat, lungs, stomach, intestinal tract, heart, and blood vessels are primarily affected. The first signs of anaphylaxis may be a red, itchy rash and a feeling of warmth. These may be followed or accompanied by light-headedness, shortness of breath, or sneezing; a feeling of anxiety; stomach or uterine cramps; and/or vomiting and diarrhea. In most cases of anaphylaxis, the symptoms go away or are reversed by treatment with epinephrine. In other rare cases, the symptoms are prolonged and may lead to death.

Foods that frequently cause anaphylaxis in allergic persons include peanuts, nuts, shellfish, eggs, and seeds. Anaphylactic reactions have also been reported in persons who have eaten milk, chocolate, barley, rice, wheat, citrus fruits, melons, bananas, tomatoes, spinach, corn, potatoes, and soybeans. However, any given food protein can be troublesome, depending on the individual.

More recently, cases of food-related anaphylaxis have occurred in patients who perform aerobic exercises within several hours of a snack. It appears that these reactions can be avoided if the snack and the exercise are separated by at least four hours.

Skin & Respiratory Reactions Caused by Foods
The most common allergic skin reaction to a food is hives. Hives are red, very itchy, swollen areas of the skin. They arise suddenly and can disappear quickly, and often appear in clusters, with new clusters appearing as other areas clear. Hives may occur alone or with any of the symptoms listed under anaphylaxis.

Atopic dermatitis is an occasionally transient, but more likely chronic, itchy inflammation of the skin often occurring in individuals with personal or family histories of allergic rhinitis or asthma. The role of specific food allergens' effect on atopic dermatitis has been a matter of debate. Many physicians support that exposure of an infant to food allergens (especially milk) and even food exposures encountered during pregnancy and through breast feeding can worsen atopic dermatitis. Recent studies have indicated a relationship between food hypersensitivity and a worsening of the rash in some children with atopic dermatitis.

Nasal allergy may occasionally be the respiratory tract's reaction to food allergens, although such reactions are caused more commonly by intolerance. Symptoms of nasal allergy, often referred to as "hay fever," include itching of the nose or roof of the mouth, sneezing, and difficulty breathing through the nose. Symptoms of eye allergy can include itchy, red, and tearing eyes.

Asthma, the condition in which the airways of the lung narrow, may sometimes be related to food allergy. Most cases of asthma caused by a food allergen occur in infants and are frequently connected to cow's milk sensitivity. Foods, however, do not seem to play a frequent role in triggering asthma in adults.

Gastrointestinal Reactions Caused by Foods
The most common symptoms one might be likely to experience are vomiting, diarrhea, and abdominal cramping. Other less common symptoms may include a red rash around the mouth, itching and swelling of the mouth and throat, nausea, abdominal pain, swelling of the stomach, and gas. Although diarrhea and vomiting are the two most common symptoms of food allergy reactions, these symptoms are not necessarily caused by allergy. They may also signify food intolerance or other problems, such as parasites or infections. In fact, lactose intolerance is a major cause of adult diarrhea, and in infants, reactions to certain foods, especially fruits, cow's milk, egg white, peanuts, and wheat are common.

Some of these reactions, such as a rash around the mouth, due to natural acids in foods like tomatoes and oranges, or diarrhea, due to excess sugar in fruit juice or other beverages, are non-allergic in nature and are usually temporary problems. Other reactions, though, are truly allergic and may be caused by other traces of the offending food when eaten again.

As the child becomes older, however, even those foods which previously caused allergic reactions may be tolerated by the maturing immune system. Therefore, periodic food allergy check-ups with appropriate food testing should be carried out under the supervision of an allergy specialist.

Adverse Reactions to Food Additives
Currently, food intolerance caused by chemical food additives is an increasing concern. The symptoms of some of these reactions can mimic allergic reactions. The food and drug dye tartrazine (yellow-FD & C No. 5) has been shown to cause asthma in some aspirin-sensitive asthmatics. Mixed colors, particularly red and yellow dyes of this type, may produce a drug-like effect and worsen the problem in some children who are hyperactive.

The "Chinese restaurant syndrome," which is characterized by anxiety, a flushed face and pressure in the chest, is suspected to be caused by large amounts of the flavor enhancer monosodium glutamate (MSG). Some preservatives (BHT/BHA) and coloring agents (yellow dye) have been linked to a few cases of chronic hives in adults.

Another type of preservative, sulfites, are used in some restaurants as "stay fresh" agents, particularly in the form of chemicals sprayed on salads to prevent wilting and browning edges. Sulfites also can be found in some processed foods and beverages, including fresh shrimp, mushrooms, potato chips, dried fruits, and wine. Sulfites can cause serious asthma attacks in some sulfite-sensitive asthmatics, especially adult asthmatics who require regular medication. These reactions can result in hives, shock or even death. Though figures vary, studies have indicated at least six percent of all asthmatics are likely to be at risk for sensitivity to these preservatives.

Preventing Food Sensitization & Allergy
No study has proven that avoidance of cow's milk in infancy prevents food allergy; however, some evidence suggests that using breast milk in early infancy may result in a delayed or lower rate of occurrence of other forms of allergy. The nursing mother also should avoid foods that may cause her infant to become allergic. However, no nursing mother should make alterations in her own diet without first consulting her physician or the baby's pediatrician. Unsupervised dietary eliminations could potentially result in nutritional deficiencies which would affect both the mother and the unborn child. Although cow's milk is the chief cause of food allergy in infants, other foods, including eggs, chicken, beef, wheat and other cereals, fish, and citrus fruits, may also cause food allergy. Some doctors recommend that solid food not be fed to a baby during the first six months of life, especially if allergy is prominent in the child's family.

Diagnosing Food Allergy
An allergist diagnoses food allergy by carefully assessing the problem in an organized, detailed and painstaking manner. There are no "quick fixes" to the evaluation and treatment of food allergy problems. First, a detailed medical history will be taken, followed by a physical examination. The allergist will then inquire about the frequency, seasonality, severity, and nature of the symptoms. The patient will also be asked about how much time elapses between eating a food and the reaction.

The allergist may suggest keeping a food diary to aid in narrowing down the food allergy. A food diary is a detailed record of foods eaten that lists date, time, and any symptoms that occurred afterward.

When an allergy to a single food is suspected, the allergist may recommend eliminating the food for a time, a standard technique for diagnosing food allergies. If the symptoms are relieved, the allergist may add the food to the diet once again to see what happens. When a food allergy is suspected on the basis of frequent or continuous symptoms, no single food may be identified as the likely offender. A diet in which several suspected foods are eliminated may be recommended, or a non-allergic food substitute might be suggested for a period of time.

Allergy skin testing may be helpful in determining which foods cause an allergic response. Skin testing may also help to rule out food allergy rather than food intolerances. It is rare for someone with a negative skin test to have a positive reaction to an objective food challenge. (Food challenges are explained later in this section.)

Skin testing involves placing a small amount of liquid extract made from the food on the patient's back or arm. A needle is then passed through the liquid on the top layer of skin (called a prick test), or small scratches are made through the liquid and the top layer of skin (called a scratch test). The development of any wheal (bump) within 20 minutes indicates a positive response. Skin tests are not helpful when sensitivity to simple foods such as sugars or food additives is suspected. Unfortunately, skin testing with food is not as useful as it is for diagnosing other allergies.

Blood tests (known as the RAST test) may be helpful for selected patients but are generally not as helpful as the elimination and "challenge" of a suspected food. In some cases, a food RAST blood test may be recommended by your doctor to obtain similar information as with the allergen skin test. Food cytotoxic blood tests and sublingual provocation food testing are not recommended, however, since the FDA has determined that these tests are unproven procedures to diagnose food allergies in well-controlled studies and clinical trials.

If diagnosis of food sensitivity remains in doubt after the patient has used diet diaries, eliminated certain foods, and undergone allergy tests, the allergist may recommend "blinded" food and/or food additive "challenges" in the office or hospital under close observation. Usually, the suspected food or a neutral food, called a placebo, is fed in opaque colorless capsules, or as a hypoallergenic slush or pudding (such as tapioca) so neither the patient nor the doctor knows whether the suspected food or the placebo is being eaten. This is called a "double-blind" challenge, and when properly performed is helpful in establishing a cause-and-effect relationship between a food and an allergy symptom.

Treatment of Food Allergy
Studies in children have shown that many adverse reactions to foods resolve as children get older. It's a good idea to have the child undergo food challenges at regular intervals to identify when this occurs.

There is a great deal of research going on in the field of food allergy including better methods to diagnose this problem. Medications are also being tested that may make it safer for food-allergic individuals to eat away from home. Avoiding specific foods is the best treatment method for food allergy. Allergy injections for food are not helpful or recommended, and may be dangerous. Treating food allergies with drugs may be helpful only when symptoms persist or when offending foods are likely to be eaten away from home and cannot be avoided.

Anaphylactic reactions caused by food allergies are among the few potentially life-threatening allergic conditions. Persons who have experienced an anaphylactic reaction to a food must strictly avoid it. Because the sensitive individual may be exposed to the food in an unrecognized form, in a restaurant, for instance, he or she should carry a kit containing epinephrine (adrenalin) at all times and should be taught how to inject the medication in order to be prepared for an emergency. The allergic individual should also wear an identification bracelet that describes the allergy.

Some restaurants, airlines and major hotels may help the food-allergic person avoid obviously troublesome foods. However, restaurant meals or foods that have been processed may contain small amounts of foods that need to be avoided. Therefore, a person who is highly allergic must be cautious about all restaurant foods, particularly combination foods such as soups, quiche or sauces. Again, he or she should carry a kit containing epinephrine (adrenalin).

A person who is highly allergic to a food must also read food labels carefully. Foods that have been processed may contain trace amounts of the food that needs to be avoided. For example, milk may not be one of the ingredients listed on a label. Instead, the label may list casein, sodium caseinate, or milk solids. Not every food that contains wheat identifies it as such; sometimes wheat is listed as gluten. Similarly, egg white is frequently listed as albumin. Also, cottonseed flour may be used in place of wheat flour in pastry cooking. Today, government agencies are proposing stricter regulations for food ingredient labeling so that consumers will be more aware of the existence of all food additives and preservatives.

A listing of allergy cookbooks and other informational books on food allergy can be obtained by writing to the American Academy of Allergy, Asthma and Immunology, 611 E. Wells Street, Milwaukee, WI 53202, or e-mail the Academy at

Other Resources

Allergy and Asthma Network/Mothers of Asthmatics
3554 Chain Bridge Road, Suite 200
Fairfax, VA 22030-2709

Asthma and Allergy Foundation of America
1125 15th Street NW, Suite 502
Washington, DC 20005

Food Allergy Network
10400 Eaton Place, Suite 107
Fairfax, VA 22030-2208

International Life Sciences Institute-Nutrition Foundation
1126 16th Street, NW
Washington, DC 20036

This was prepared under the direction of the American Academy of Allergy, Asthma and Immunology's Public Education Committee, in cooperation with the Asthma and Allergy Foundation of America and the National Allergy and Asthma Network.

Material is based upon information in the monograph Adverse Reactions to Food, American Academy of Allergy, Asthma and Immunology's Committee on Adverse Reactions to Foods and the National Institute of Allergy and Infectious Diseases, Anderson, J.A. and Sogn, D.D., Editors.

U.S. Department of Health and Human Services, NIH Publication #84 2442, July, 1984.

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