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Slideshow: Food Allergy Triggers, Common and Uncommon

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Peanuts

Peanuts cause more life-threatening allergic reactions than any other food. They're a legume, like soybeans, rather than a true nut. But among people with a peanut allergy, 25%-50% will also react to tree nuts, such as walnuts. Foods and ingredients to avoid include beer nuts, goobers, arachic oil, and some hydrolyzed vegetable proteins. Baked goods, sauces, even chili can contain hidden peanut proteins.

Milk and Dairy Foods

A milk allergy is the most common food allergy in children, but 80% outgrow it. Infants may need hypoallergenic or soy formula, and sometimes breastfeeding mothers need to avoid drinking milk. Milk proteins, including casein, are ubiquitous in processed foods, even found in canned tuna. If you're allergic to cow's milk, goat's milk may not be safe, either. Lactose intolerance is not an allergy, but a digestive problem.

Eggs

Eggs are the second most common cause of food allergy in children, although they usually outgrow this allergy, as well. Read the labels carefully for noodles, mayonnaise, and baked goods. Eggs can also be found in some unlikely products: the foam topping in drinks or the egg wash on pretzels. Eggs are used to produce the influenza vaccine, so check with a doctor before getting the flu vaccine.

Shellfish

An allergy to shellfish most often develops in adulthood, and it is a lifelong allergy. Shrimp, crab, crawfish, and lobster -- crustaceans -- produce the most severe allergic reactions. Mollusks can trigger reactions, too: clams, mussels, scallops, escargot, octopuses, and squid. People allergic to shellfish should avoid steam tables or stovetops where shellfish is cooked because the vapors can trigger a reaction.

Tree Nuts

Walnuts, almonds, pecans, hazelnuts, cashews, pistachios, Brazil nuts, and pine nuts may all be off limits if you have a tree nut allergy. These must be clearly labeled in packaged foods, but nuts are more difficult to avoid in restaurants and bakeries. Nutmeg, water chestnuts, sunflower seeds, and sesame are not nuts and can be eaten safely. Be aware that tree nut oils, such as shea oil, may be used in skin lotions.

Finned Fish

The protein in finned fish can cause severe allergies, most commonly from eating salmon, tuna, or halibut. If you're allergic to one type, you may react to others, too. Many ethnic restaurants flavor dishes with fish sauces. So tread carefully in Thai and Chinese restaurants, and beware of Caesar dressing and Worcestershire sauce, made from anchovies. Some people can safely eat canned tuna and salmon, but not fresh fish.

Soy

If you're allergic to soy, you need to read the fine print very carefully on food labels. Soy protein is widely used in breads, cookies, canned soups, processed meats, and snack foods. Foods to avoid include edamame, (young green soybeans), tofu, soy milk, miso, and soy sauce. Most people with soy allergy can still eat soy oil and soy lecithin. Soy allergy is more common among babies and children.

Wheat

Wheat allergy is an allergic reaction to one of four proteins in wheat. You do not necessarily react to the gluten. People allergic to wheat can usually eat other grains, including barley, oats, rye, corn, and rice. Wheat allergy is more common among children and is often outgrown. Bulgur, couscous, and farina contain wheat protein, and many products, including beer, salad dressing, and processed meats, may contain wheat.

Contrast: Gluten Intolerance

People with celiac disease have an autoimmune disorder that is triggered by gluten, a protein in wheat, rye, and barley. Eating gluten actually damages the small intestine. Symptoms include diarrhea, bloating, weight loss, chronic fatigue, and weakness -- but not the skin rashes, swelling, or wheezing seen with a food allergy. Some people may have gluten intolerance that is a digestive problem and not immune-related. Celiac disease can be diagnosed with a blood test.

How a Food Allergy Begins

With the first exposure to a trigger food, your body treats it as something harmful and creates immunoglobulin E antibodies in your blood stream. You won't notice symptoms at the first exposure, but your body is primed to release histamine the next time. Although some food allergies are more common among young children, food allergies can develop at any time in life.

Food Allergy Symptoms

Symptoms usually occur within a few minutes to two hours after eating the food. Reactions range from mild to severe and can include:

Hives or other skin rash
Tingling or itching in the mouth
Swelling of face, tongue, or lips
Coughing or wheezing
Vomiting, diarrhea, or abdominal cramps
Swelling of throat and vocal chords
Difficulty breathing

Anaphylaxis: Severe Reaction

Mild symptoms can sometimes progress to a dangerous condition known as anaphylaxis, so it's important to act quickly. This life-threatening reaction involves constricted airways, throat swelling that may cause suffocation, and a large drop in blood pressure. Doctors often prescribe epinephrine injections such as EpiPen or Twinject to carry and use at the first sign of a reaction. You should still go to an emergency room for evaluation.

Myth: Food Allergy Is Predictable

If one bite of seafood went down OK last time, will you always be safe with one bite? Maybe, maybe not. In general, your reaction will depend on the extent of your allergy and the amount of the food you eat. But reactions can be unpredictable, so you may have hives once but vomiting or breathing problems on a different occasion.

Contrast: Food Intolerance

Trouble digesting a food isn't the same thing as a food allergy. An allergy occurs as an immune reaction. Food intolerance, such as lactose intolerance, can cause bloating, cramps, and diarrhea, but it doesn't cause an immune system reaction. Lactose intolerance occurs when the body doesn't produce enough lactase, an enzyme that breaks down lactose, the sugar found in milk and dairy products.

Contrast: Food Additives

A reaction to food additives also can be confused with food allergy. Monosodium glutamate (MSG), a flavor enhancer, can cause flushing, warmth, headache, and chest discomfort. Sulfites, sometimes used to prevent mold growth, can cause breathing problems for people who have asthma. Sulfites also are found in wine and other products. The FDA requires labeling of sulfites and bans their use as a preservative on fruits and vegetables.

Variant: Oral Allergy Syndrome

An allergy to certain raw (not cooked) fruits and vegetables is known as oral allergy syndrome. It occurs most often in people who have hay fever, especially hay fever triggered by birch or ragweed pollen. Raw produce such as apples, cherries, kiwis, celery, tomatoes, and green peppers may cause tingling, itching or swelling of the lips, tongue or throat, watery or itchy eyes, a runny nose, and sneezing.

Exercise-Induced Food Allergy

This food allergy only occurs when the food is eaten just before exercising. The rise in body temperature and the food trigger the reaction, which can range from itching, hives, or lightheadedness to anaphylaxis. The foods most often associated with exercise-induced allergy are crustacean shellfish, alcohol, tomatoes, cheese, and celery.

Elimination Diet

Sometimes a reaction is immediate after eating a particular food. But if you're not sure what caused your reaction, you may begin by keeping a diet diary and working with a health professional. In an elimination diet, you eliminate one food at a time from your diet. This may help you figure out which food is causing your problem.

Allergy Testing

In a skin prick test, an allergist places a drop of solution on your skin, then pricks the skin to allow it to penetrate. A negative result means you are not allergic, but there are sometimes false-positive results. A blood test measures antibodies to a particular food and also can produce false positives. Your doctor also may give you a medically supervised food challenge to see if you react to a food.

Outgrowing Allergies

Children are likely to outgrow allergies to milk, egg, wheat and soy but to have lifelong allergies to peanuts, tree nuts, fish, and shellfish. Blood tests for food-specific antibodies may help determine whether the child has outgrown an allergy. A doctor may supervise a "food challenge" to see if the child has outgrown the allergy. Do not try a food challenge on your own. Even a small amount of a food may produce a life-threatening reaction in some people.

Living With Food Allergies

There is no cure for food allergies, so you need to avoid the food that causes a reaction. The Food Allergen Labeling and Consumer Protection Act requires labeling of the eight major causes of food allergy. Call 911 at signs of anaphylaxis (wheezing, trouble breathing, dizziness) and use an epinephrine injection. Maintain a food allergy action plan for yourself or your allergic child. You may want to wear a medical ID bracelet indicating the allergy.