"The prevalence of food allergy is growing and probably will continue to grow along with all allergic diseases," says Dr. Robert A. Wood, director of the pediatric allergy clinic at Johns Hopkins Medical Institutions in Baltimore. Wood says research over the last three decades indicates that the number of people with allergies is skyrocketing in developed and developing countries.

Allergies are the immune system's incorrect response to what is normally a harmless substance; in the case of food-based allergies, the harmless substance could be peanuts, eggs or even milk.

Once the immune system decides that a particular food is harmful, it creates specific antibodies to it. The next time the individual eats that food, the immune system releases massive amounts of chemicals, including histamine, in order to protect the body. These chemicals trigger a cascade of allergic symptoms that can affect the respiratory system, gastrointestinal tract, skin or cardiovascular system.

An allergic reaction is the result of how three factors interact with the body:

1. Allergen: The allergens that cause 90 percent of all food-allergic reactions are shellfish (for example, shrimp, lobster, crab), fish, peanuts, tree nuts (for example, walnuts, cashews), milk, eggs, soy and wheat.

2. Mast cells: Although mast cells are found throughout the body, most reside in connective tissues such as those of the skin, the tongue, the lining of the nose and intestinal tract, the lungs and the upper airways.

3. Immunoglobulin E: IgE is an allergic antibody, a type of protein made by the immune system to recognize and fight specific body "invaders." IgE coats the surface of the mast cells in tissues.

The first time an allergy-prone person is exposed to an allergen, large amounts of the corresponding IgE antibodies are produced. The IgE antibodies cause the mast cells to release inflammatory chemicals that cause swelling of tissues, as well as histamine and several other chemicals that cause itching, engorgement of blood vessels, increased secretions and bronchospasm (tightening of muscles that surround the airways).

If the allergen is in the air, the allergic reaction will occur in the eyes, nose and lungs. If the allergen is eaten, the allergic reaction will occur in the mouth, stomach and intestines. Sometimes enough inflammatory chemicals are released to cause a systemic reaction throughout the body. This severe type of reaction is called anaphylaxis and can be life-threatening.

People usually inherit the ability to form IgE antibodies against food. Those most likely to develop food allergies come from families in which hay fever, asthma or eczema are common.

Typical and often unnoticed food allergy symptoms are dark circles under the eyes ("allergic shiners"), puffiness under the eyes, chronic (noncyclic) fluid retention and chronic swollen glands.

Other more obvious symptoms may be present and can typically appear within minutes to two hours after a person has eaten the offending food. The affected person may experience a tingling sensation in the mouth, swelling of the tongue and throat, difficulty in breathing, hives, vomiting, abdominal cramps, diarrhea, a drop in blood pressure or loss of consciousness.

An estimated 150 Americans die each year from severe allergic reactions to food, says food allergy expert Dr. Hugh A. Sampson, director of the Elliot and Roslyn Jaffe Food Allergy Institute at Mount Sinai School of Medicine in New York City.

Scientists estimate that approximately 11 million Americans suffer from true food allergies. At the present time, there is no cure; avoidance is the only way to prevent an allergic reaction. Unfortunately, some of these problem foods are hidden as ingredients in commercially prepared foods and are therefore difficult to avoid, especially when instances of unintentional inclusion of allergens can occur in commercial food through poor cleaning and cooking schedules or improper cleaning of utensils.

The Food Allergy & Anaphylaxis Network (www.foodallergy.org or 800.929.4040) has been an advocate for simple, clear and accurate food labels for more than a decade.

"Reading food labels is the only way that food-allergic consumers can avoid dangerous allergens in packaged food," says Anne Muñoz-Furlong, network founder and president. She notes that today there are still more than a dozen ways to indicate the presence of milk protein without using the word "milk." Current labeling guidelines allow the use of the term "non-dairy" when foods contain milk derivatives such as casein.

In addition to the network's monitoring of hidden and unlabeled sources of allergens, the U.S. Food and Drug Administration maintains an informative website by the Center for Food Safety and Applied Nutrition (www.cfsan.fad.gov/~dms/wh-alrgy.html).

The "rotary diversified diet" has helped some to control dietary allergies. Check with your health care professional, your librarian or your web search engine for more information.