Food Allergies: When Eating Is Risky

by Food and Drug Administration (FDA)

Do you start itching whenever you eat peanuts? Does seafood cause your stomach to churn? Symptoms like these cause millions of Americans to suspect they have a food allergy.

But true food allergies affect a relatively small percentage of people: Experts estimate that only 2 percent of adults, and from 2 to 8 percent of children, are truly allergic to certain foods. Food allergy is different from food intolerance, and the term is sometimes used in a vague, all-encompassing way, muddying the waters for people who want to understand what a real food allergy is.

"Many people who have a complaint, an illness, or some discomfort attribute it to something they have eaten. Because in this country we eat almost all the time, people tend to draw false associations [between food and illness]," says Dean Metcalfe, M.D., head of the Mast Cell and Physiology Section at the National Institute of Allergy and Infectious Diseases. For example, food intolerance may produce symptoms similar to food allergies, such as abdominal cramping. But while people with true food allergies must avoid offending foods altogether, people with food intolerance can often eat small amounts of the offending food without experiencing symptoms.

Lactose intolerance, for instance, is sometimes mistaken for milk allergy. Lactose intolerance is a problem of digestion due to an enzyme deficiency, with cramps and diarrhea the common hallmarks. Estimates are that about 80 percent of African- Americans have lactose intolerance, as do many people of Mediterranean or Hispanic origin. It is quite different from the true allergic reaction some have to the proteins in milk. Unlike allergies, intolerances generally intensify with age.

Dangerous Dishes

For people with true food allergies, the simple pleasure of eating can turn into an uncomfortable — and sometimes even dangerous — situation. For some, food allergies cause only hives or an upset stomach; for others, one bite of the wrong food can lead to serious illness or even death.

FDA regulates drugs used to treat severe allergic reactions and has recently issued regulations under the Nutrition Labeling and Education Act of 1990 to make such reactions less likely. The early Greek philosopher and physician Hippocrates was one of the first to note that cow's milk caused health problems for some people, but it was not until the early 1900s in Europe that the first scientifically documented food allergy reports began to appear. The word "allergy" is derived from a Greek word meaning "altered reaction," and initially conveyed the idea that certain substances could cause adverse reactions in some people while having no effect on the public at large.

By the mid-1920s, allergists had defined food allergy as an abnormal response of the immune system to an otherwise harmless food. Food allergens, those parts of food causing allergic reactions, are usually proteins. When the allergen passes from the mouth into the stomach, the body recognizes it as a foreign substance, producing antibodies to halt the invasion. In allergic individuals, as the body fights off the invasion, symptoms begin to appear throughout the body. The most common sites are the mouth (swelling of the lips or tongue, itching lips), digestive tract (stomach cramps, vomiting, diarrhea), the skin (hives, rashes or eczema), and the airways (wheezing or breathing problems). Food allergies are much more common in infants and young children, who often later outgrow them. Increased susceptibility of young infants to food allergic reactions is believed to be the result of immunologic immaturity and, to some extent, intestinal immaturity. Older children and adults may lose their sensitivity to certain foods if the responsible food allergen can be identified and completely eliminated from the diet, although some food allergies can last a lifetime.

Heredity may cause a predisposition to have allergies of any type. Some experts believe that, rarely, a specific allergy can be passed on from parent to child. Several studies have indicated that exclusive breast-feeding, especially with maternal avoidance of major food allergens, may deter some food allergies in infants and young children. (Smoking during pregnancy can also result in the increased possibility that the baby will have allergies.) Most patients who have true food allergies have other types of allergies, such as dust or pollen, and children with both food allergies and asthma are at increased risk for more severe reactions. Repeated exposure to allergens starts sensitizing those who are susceptible. Cow's milk, eggs, wheat, and soy are the most common food allergies in children. An early peanut allergy may be lifelong. Adults are usually most affected by nuts, fish, shellfish, and peanuts.

Life-Threatening Reactions

The greatest danger in food allergy comes from anaphylaxis, a violent allergic reaction involving a number of parts of the body simultaneously. Like less serious allergic reactions, anaphylaxis usually occurs after a person is exposed to an allergen to which he or she was sensitized by previous exposure (that is, it does not usually occur the first time a person eats a particular food). Although any food can trigger anaphylaxis (also known as anaphylactic shock), peanuts, tree nuts, shellfish, milk, eggs, and fish are the most common culprits. As little as one-fifth to one- five-thousandth of a teaspoon of the offending food has caused death.

Anaphylaxis can produce severe symptoms in as little as 5 to 15 minutes, although life-threatening reactions may progress over hours. Signs of such a reaction include: difficulty breathing, feeling of impending doom, swelling of the mouth and throat, drop in blood pressure, and loss of consciousness. The sooner anaphylaxis is treated, the greater the person's chance of surviving. The person should be taken to a hospital emergency room, even if symptoms seem to subside on their own.

There is no specific test to predict the likelihood of anaphylaxis, although allergy testing may help determine what a person may be allergic to and provide some guidance as to the severity of the allergy. Experts advise people who are susceptible to anaphylaxis to carry medication, such as injectable epinephrine, with them at all times, and to check the medicine's expiration date regularly. Doctors can instruct patients with allergies on how to self- administer epinephrine. Such prompt treatment can be crucial to survival.

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