Allergic Reactions to Foods

Scores of the ordinarily harmless substances in foods, the air, and objects we touch can provoke symptoms ranging from a runny nose and hives to fatal anaphylaxis.

Allergies occur when our immune system overreacts to minute amounts of foreign substances. Of these, food allergies make up only a small percentage. Far more common are allergic reactions to pollen and other inhaled substances, medications, and substances that are absorbed into the skin.

Doctors do not completely understand why so many people have allergies, though heredity is instrumental. If both parents have allergies, their children will almost always follow suit, although the symptoms arid allergens may be quite different. Food allergies in infants and children, however, tend to lessen as they grow, and the problem may disappear by adulthood.

Allergies basically develop in stages. When the immune system first encounters an allergen (or antigen) a substance that it mistakenly perceives as a harmful foreign invaders signals specialized cells to manufacture antibodies, or immunoglobulins, against it. The person will not experience an allergic reaction in that initial exposure; however, if the substance again enters the body, the antibodies programmed to mount an attack against it will go into action. In some instances, the response will not produce symptoms; but the stage will have been set. At some future date, an antigenantibody reaction may provoke cells in the immune system to release large amounts of histamines and other chemicals that are responsible for an allergic response. When this happens, symptoms can range from something as mild as a sneeze or runny nose to an extremely serious reaction, such as sudden death.

Common Symptoms

The most common symptoms of food allergies are nausea, vomiting, diarrhea, constipation, indigestion, headaches, skin rashes or hives, itching, shortness of breath (including asthma attacks); and, in severe cases, wide spread swelling of the skin and mucous membranes. Swelling in the mouth or throat is potentially fatal because it can block the airways to the lungs. In the most severe cases, anaphylactic shock a life threatening collapse of the respiratory and circulatory system-may develop.

The allergen usually provokes the same symptoms each time, but many factors affect their intensity, including stress, how much of the offending food was eaten, how it was prepared, and whether it was eaten with other foods. Some people can tolerate small amounts of an offending food; others are so hypersensitive that they react to even a minute trace. Most allergic reactions arise quickly, usually within a few minutes or up to 2 hours after the allergen enters the body. In unusual cases, however, the reaction may be delayed for up to 48 hours, making it more difficult to identify the allergen.

Pinpointing Allergens

Some allergens are easily identified because characteristic symptoms will develop immediately after eating the offending food. In other instances, it may be necessary to keep a carefully documented diary of the time and content of all meals and snacks and the appearance and timing of any subsequent symptoms. After a week or two, a pattern may emerge. If so, eliminate the suspected food from the diet for at least a week, and then try it again. If symptoms develop only in the latter part of this experiment, chances are you have identified the offending food.

In more complicated cases, allergy tests may be required. The most common are skin tests; food extracts are placed on the skin, which is then scratched or pricked, allowing the penetration of a small amount of the extract. Development of a hive or itchy swelling usually indicates an allergic response. In some cases, a doctor may order a RAST (radioallergosorbent test) blood study in which small amounts of the patient's blood are mixed with food extracts and then analyzed for signs of antibody action. This test is more expensive than skin tests but may be safer for hypersensitive people, who may have a severe reaction to the skin test.

Still other tests may involve a medically supervised elimination diet and challenge tests. In one variation, the patient is put on a hypoallergenic diet of foods that are unlikely to cause allergies for example, lamb, rice, carrots, sweet potatoes, and pears for 7 to 10 days, at which time all allergic symptoms should completely disappear. (If they don't, a reaction to something other than food should be suspected.) The doctor then administers small amounts of food or food extracts, usually in capsule form, to see if an allergic response occurs.

Warning: Some people put themselves on highly restricted diets without proper medical consultation. This can result in serious nutritional deficiencies; it is best to consult a doctor.

Living With Allergies

Once the offending allergens have been identified, eliminating those foods from the diet should solve the problem. But this can be more complicated than it sounds. Some of the most common food allergens, such as milk, eggs, wheat, and corn, are hidden ingredients in many processed foods. When you shop, scrutinize all food labels carefully. Also, many foods are chemically related; thus, a person allergic to lemons may also be allergic to oranges and other citrus fruits. In some cases, the real culprit may be a contaminant or an accidental additive in food. For example, some people who are allergic to orange juice and other citrus juices may actually be able to tolerate the peeled fruits themselves, since it is limonene, the oil in citrus peels, that often produces the allergic reaction. Some people only experience food allergy symptoms if they consume the offending food just before exercising.

Eating out can pose a few problems. When invited to someone's home, let your host know in advance if you are allergic to specific foods. Or ask about the menu; if it presents problems, offer to bring a substitute dish for yourself. Usually, however, it's sufficient to make inquiries upon arrival and then quietly decline the problem dishes.

In restaurants, ask servers about food ingredients before ordering. If they are unable to answer your questions, ask that they be directed to the chef. In order to avoid potential allergens, some people will have to select simple, ungarnished dishes, such as unseasoned broiled fish, a baked potato, and steamed vegetables. Or call the restaurant ahead of time to request that food be specially prepared.

Treating Emergencies

If you have had or your doctor believes you are susceptible to-severe hives, asthma attacks, or anaphylactic reactions, you should always wear a medical identification pendant or carry emergency medical information in your wallet or purse. Your doctor may also recommend that you carry anti-histamine medication or an easy-to-inject form of epinephrine (Adrenalin) to use in case of breathing problems or another severe allergic reaction.

A Different Problem

Many people mistakenly assume they have food allergies when, in fact, the problem is intolerance. The symptoms may be similar, but an allergic reaction is mediated through the immune system, whereas food intolerance originates in the gastrointestinal system and entails an inability to digest or absorb certain substances.

One of the most common types is lactose intolerance, in which a person lacks an enzyme (lactase) needed to digest milk sugar. The degree of lactose intolerance varies in different people. In severe cases even a tiny amount of milk sugar may provoke symptoms-generally abdominal pain and bloating, diarrhea, and flatulence.

However, lactose reduced dairy products are available, as are tablets that can be taken before eating; these have the enzyme that makes digesting dairy products possible. In contrast, a person who is allergic to milk will still have symptoms after ingesting even lactose-free milk products.

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