Eight foods comprise 90 percent of all food allergies. They are peanuts, tree nuts, wheat, milk, eggs, soy, shellfish, and fish. A person may be allergic to just one of these foods, or may have multiple allergies to two or more of these substances.

Peanuts

An allergy to peanuts is the most publicized and widely known because news reports have pointed out spectacular anaphylactic reactions to unbelievably minute quantities of the peanut protein. There are a few reasons why peanut allergies can be so severe.

The protein responsible for the allergy has a unique shape that is very easy for your immune system to recognize. All proteins have bends and folds in their structures, but the peanut proteins are folded so the allergenic molecules are right on the surface.

Three specific protein molecules in peanuts, called Ara h 1, 2, and 3, provoke an allergic reaction. Your immune system has three times the targets and three times the potential response with peanuts compared to other foods that generate allergic reactions. The antibody in your blood that is created when you have a peanut allergy is called PN-IgE.

Milk

Two main types of milk allergies exist: slow onset and rapid onset. Rapid onset can occur within minutes of consuming the milk protein. Symptoms include itching, hives, difficulty breathing, and anaphylaxis. It is less common than slow onset, which is manifested in vomiting, fussiness in babies, and failure to thrive. The slow-onset allergy can be more difficult to diagnose, as the RAST test isn't very accurate for this type.

Most milk allergies are reactions to both the casein and whey portions of the milk protein. The casein protein is heat stable, that is, cooking will not destroy its configuration. Heated milk products are therefore still allergenic. Whey is not heat stable, so if your allergy is to the protein in whey only, you may be able to consume heated milk products.

When you're looking for milk or cheese substitutes, it can help to look for the word “vegan.” Vegan means that no animal products whatsoever were used in making that food. The word “pareve” can also be a good clue. This is a kosher term meaning no dairy or meat.

The good news about milk allergies is that most children outgrow them after avoiding milk and milk products for one to two years. However, if a young child is allergic to milk, the odds are fairly good that she will develop allergies to other foods as well.

Fish and Shellfish

There is usually no cross-reactivity to shellfish (shrimp, crab, and lobster) and finfish (grouper, haddock, walleye), but some people are allergic to both. If you have a severe allergy to one or the other, it's best to simply avoid both.

This allergy can, and does, occur at any time of life, not only in childhood. It's a tricky allergy to manage because of cross-contamination. Crosscontamination in this subgroup can occur when the oil used to fry shrimp is then used to cook French fries. Or a spoon that contained fish-based Worcestershire sauce could contaminate a salad.

Fish proteins can even become airborne during the cooking process and can cause reactions. Make sure the fish you do eat is very fresh. Fish that has begun to spoil will have a buildup of histamine in the flesh, which can cause a reaction even in people who are not allergic. Iodine is not the cause of fish allergies, as many people believe; the reaction is to the protein in fish.

Eggs

The proteins in egg whites cause most of the allergic reactions in people who are allergic to eggs. Uncooked or poorly cooked egg whites can cause the most severe reactions. But some people are also allergic to the proteins in egg yolks. This is another one of the very serious reactions that can be life threatening. Some people who are allergic to eggs can even get a reaction from skin contact with egg products or from inhaling fumes from cooking eggs.

One of the best ways to avoid eggs is to read labels. With the new labeling requirements now in effect, look for terms such as “made in a facility that also processes eggs.” But, as with all processed foods, mistakes can happen. It's a good idea to become familiar with the names eggs can hide behind in processed foods, and scan the ingredient list even if the label reassures you the product doesn't contain egg. Again, the word “vegan” is probably your best clue, because these foods are made with no animal products whatsoever.

People generally outgrow egg allergies. Most allergies begin in young children, who outgrow the reaction by age five. Food challenges are usually used to diagnose egg allergies.

Some vaccines, including the flu vaccine and the shot for measles/ mumps/rubella, are developed and made using egg proteins. Your doctor can actually test the vaccine to see if it contains egg proteins before it is administered to you or your child.

Wheat

An allergy to wheat is sometimes a reaction to the gluten, or protein, found in wheat and some other grains; other times it's a reaction to the grain itself. A pure reaction to wheat is different from celiac disease, also known as celiac sprue. Some researchers think gluten allergies may go far beyond celiac disease, and if there are IgE antibodies to gluten in the blood, avoiding gluten may improve symptoms.

If you are allergic to wheat, you may also want to avoid barley, rye, triticale, and perhaps oats. Cross-contamination can be a problem with wheat allergies, so make sure the grains you consume are pure, from the field to the packing plant.

Starting in 2008, the Food and Drug Administration tightened guidelines for food labeling. Standards apply to products labeled “gluten free,” which help people who are allergic to gluten more readily identify safe foods. Guidelines labeling other allergenic foods were put into effect in January 2006. However, there is a caveat with this rule. The claim “gluten free” will only apply to products containing wheat. Oats, barley, rye, and triticale, which can be sources of gluten through cross-contamination, are not included in this claim, so you still must read labels carefully.

Gluten can hide in lots of foods that seem innocuous. Thoroughly study labels on all the processed foods you buy and learn about these hidden sources. The only way to be safe is to examine labels on all foods more complicated than lettuce. Gluten can be found in some unlikely places including:

Sour cream, ice cream, and cheese

Nondairy creamers

Meat patties and sausages

Soy meat substitutes

Malt flavoring and caramel coloring

Rice mixes and seasoning mixes

Some medications

Canned soups and bouillon cubes

Salad dressing, mustard, flavored vinegars, and mayonnaise

Canned baked beans and vegetables with sauces

Nonstick baking sprays with flour

Cocoa mixes and chocolate drinks

Wheat allergies can be difficult to diagnose because skin tests and blood tests are usually inconclusive. An elimination diet, under the supervision of a doctor or nutritionist, may be your best bet.

Soy

Soy is a legume, as are peanuts. If you are allergic to peanuts, you may have a cross-reactivity to soy or other legumes, including chickpeas, lima beans, and Great Northern beans. But an allergy to one does not guarantee an allergy to another.

It's rare for adults to develop an allergy to soy. Soy allergies usually develop at around three months, and many children outgrow it. The allergy usually begins as a reaction to soy-based formulas; breastfeeding is one of the best ways to prevent allergies to soy and milk.

Soy can hide behind certain terms in food that aren't included in labeling laws. “Vegetable protein” and “natural flavors” are blanket terms manufacturers are allowed to use for products that can contain soy. Monoglycerides and diglycerides may be derived from soy, so avoid foods that include those terms on the label.

Some of the symptoms more unique to soy allergies include skin reactions such as eczema and acne, along with canker sores and hives. These reactions are more uncomfortable than life threatening, although an anaphylactic reaction is still possible. For mild reactions, taking an antihistamine will help reduce symptoms.

You have five different types of taste buds on your tongue: sweet, salty, sour, bitter, and umami. Umami is less commonly known and understood. In 2000, researchers isolated the receptor for umami and officially added it to the types of taste buds. It is a “meaty” taste triggered by the presence of glutamate amino acids, found in soy sauce, mushrooms, and monosodium glutamate.

If you are allergic to soy, you must omit soy sauce from your diet, or use a substitute you make at home. You'll have to carefully read labels of medications, too. Some of the fast-melt medicines are soy-based.

Tree Nuts

As with peanut allergies, tree-nut allergies can be very severe and usually last your entire life. If you have an allergy to peanuts, there is about a 40–50 percent chance you will develop an allergy to tree nuts as well. Nuts can hide in processed and prepared foods, and cross-contamination is a great risk, even if the food has been properly labeled. Avoid all nut butters and pastes as well. Tree nuts include:

Walnuts

Pecans

Pistachios

Chestnuts

Hazelnuts

Almonds

Macadamia nuts

Cashews

Beechnuts

Brazil nuts

Nut oils may or may not be safe for you to eat. The processing that extracts oil from nuts usually removes the allergenic proteins. But if you have a severe allergy, it's best to simply avoid all nut oils. Natural extracts such as almond extract should also be avoided. Also be aware that nut products and oils can be found in some lotions and shampoos; skin contact can trigger a severe reaction in people with these allergies.

Coconut, water chestnuts, and nutmeg are not part of the tree-nut family. Unless you are specifically allergic to these foods, they don't cross-react with the tree-nut families.

• Why Are Cases Increasing?
• Cross-Contamination