While food allergies are more common in children, they may develop at any age. In general, however, they tend to diminish in severity or disappear entirely later in life. Hereditary factors have been implicated in their development, and individuals with a personal or family history of atopy (asthma, hay fever, or eczema) appear at somewhat greater risk for them. Although any food is potentially allergenic, the foods most commonly implicated in immediate hypersensitivity reactions include eggs, milk, wheat, peanuts, soybeans, chicken, fish, nuts, shellfish, and mollusks.

The complexity of our modern diets makes the avoidance of food allergens more difficult than you might think. Without your knowing it, you may be eating all kinds of derivatives of foods that you are allergic to. For example, if you have an allergy to corn, you must also be wary of corn-derived additives such as caramel coloring, citric acid, xanthin gum, lecithin, modified food starch, and malto-dextrin. And if you are super-sensitive to corn, you may run into problems from just licking a postage stamp whose sticky side is coated with a corn derivative.

Milk is another good example. Besides being in numerous dairy products such as creams, cheeses, and yogurts, it may also be found, though less obviously, in caramel coloring, lactic acid, and calcium lactate. Soy, too, which is found in texturized vegetable protein as well as the soybean by-products of glycerin and tocopherols, may be difficult to avoid. What is clear is that just knowing the specific foods you are allergic to and avoiding them may not be enough. You must also know their derivatives and in which products they may be found.

Interestingly, despite the widely held notion that tomatoes and citrus fruits are frequent food allergens, well-designed medical studies have not supported this contention to date. Moreover, some people most certainly develop hives after eating strawberries, but no studies have been able to demonstrate an allergic (IgE antibody) basis for the reaction.

Food Contaminants
Allergies to contaminants in certain foods must be distinguished from true allergies to the foods themselves. For example, an allergic reaction to cheeses, dried fruits, yogurt, or wine may not actually represent an allergy to these foods per se but to the presence of certain molds that often contaminate them. Unsavory as it may sound, insect parts, which occasionally find their way into certain spices and other foods, can provoke allergies and lead to the mistaken assumption that the particular food item is at fault. And, finally, it may not be the milk itself that is responsible for all cases of supposed "milk allergy" but the bacitracin, tetracycline, or penicillin that finds its way into our milk supply after it has been fed to the herds to prevent cattle diseases.

Food Additives
Despite what has been said, it might appear that isolating the cause of a potential food allergy is a fairly easy task. You might be tempted to reason: "I ate applesauce. I broke out in hives. I am therefore allergic to apples." Unfortunately, this may not be true. These days, foods contain additives of all kinds, and this can make determining the specific allergenic agent a very difficult piece of detective work. Unlike contaminants, additives, as the term suggests, are chemicals that have been added intentionally to a product for one reason or another.

In the broadest terms, a food additive is any substance that becomes part of a food product by being added directly or indirectly. For example, many foods are fortified with vitamins and minerals to maintain or improve their nutritional value. Others contain additives to prevent spoilage and to maintain freshness, color, and flavor. Still others are used to make foods more appealing to the eye and to the palate. Finally, a wide variety of chemicals are added to foods to give body or texture, or to enhance preparability.

According to the Public Health Service, approximately twenty-eight hundred substances are intentionally added to foods to produce a desired effect. Moreover, as many as ten thousand other ingredients or ingredient mixtures may be added to foods during processing, packaging, or storage. The most common food additives are sugar, salt and corn syrup, citric acid, baking soda, vegetable colors, mustard, and pepper. Taken together, these substances currently account by weight for greater than 98 percent of all the food additives used in the United States.

The following is a brief description of some common additive ingredients and the more frequent kinds of adverse reactions that have been associated with them:

1. Aspartame (NutraSweet), a non-nutritive sweetener found in numerous foods and beverages, has been linked with ordinary hives as well as a severe form of hives known as angioedema. In 1985 I reported the first proven case in the world's literature of the development of numerous nodules in the legs of a young woman who had consumed large amounts of aspartame-containing soda. The condition was fortunately reversible and entirely cleared once the patient stopped consuming the aspartame beverages.
2. Butylated hydroxyanisole (BHA) and Butylated hydroxytoluenebutylated hydroxyanisole (BHT-BHA), common antioxidants used in cereals and other grain products, have been linked to hives and other skin rashes.
3. FD&C Yellow #5 (tartrazine), a food coloring found in many foods and beverages, is another known hive provoker.
4. Monosodium glutamate (MSG), a popular flavor enhancer, especially for Chinese foods and also found in many fresh and packaged products, frozen dinners, and gourmet seasonings, has been associated with a variety of adverse reactions, including aggravation of asthma, burning sensations in the back of the neck, chest tightness, diarrhea, facial pain, headache, and nausea.
5. Nitrates and Nitrites, which serve as preservatives, flavor enhancers, and colorants in processed foods such as bacon, bologna, frankfurters, salami, sausages, and smoked fish, are known to trigger headaches and hives.
6. The parabens, including butyl-, ethyl-, methyl-, and propyl-, and their relative, sodium benzoate, are common preservatives used in many foods and drugs. They are well-recognized causes of itching, pain, skin rashes, and swelling.
7. The sulfites, including bisulfite, metabisulfite, potassium sulfite, sodium sulfite, and sulfur dioxide, are another large group of chemicals used as preservatives and container sanitizers. They are found in canned, frozen, and dehydrated fruits; beer, wine, wine coolers, and cider; pizza, processed grains, and packaged potato products; prescription drugs; salad dressings; soups; vegetables; shrimp; tea mixes, and Mexican food. They have been linked to such diverse reactions as abdominal cramps, asthma, chest tightness, diarrhea, elevated pulse rate, hives, light-headedness, lowered blood pressure, and vomiting.