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Most people have a reaction to food from time to time. Dip into salsa or spicy Indian food, and your nose starts running. Maybe you get gas from eating beans or headaches from wine. If you're lactose intolerant, you likely get diarrhea if you eat cheese or milk. These are food sensitivities or intolerances, and they are not caused by the immune system.
A food allergy is different. When you're allergic to a food, your immune system reacts abnormally to that specific food. Your allergic symptoms can range from a mild skin rash or itchy eyes to a more serious, deadly reaction called anaphylaxis.
Common Food Allergy Symptoms
True allergic reactions to food involve the body's immune system. When the body identifies a food as harmful, it produces antibodies directed against that food. The next time the food is consumed, the body mounts an immune response with the release of histamine and other chemicals that trigger allergic symptoms. A common example of a food allergy is to peanuts.
With a food allergy, symptoms may occur almost immediately or up to hours after consuming the particular food. These symptoms may affect the respiratory system, gastrointestinal tract, cardiovascular system, or the skin.
Food allergy symptoms can include
- skin rash or hives,
- swelling of the tongue and throat,
- breathing problems including asthma,
- vomiting or diarrhea, and
- abdominal pain and cramping.
Severe allergic reactions may result in a drop in blood pressure, loss of consciousness, or even death.
Food intolerance is different from food allergy in that it does not involve an immunologic reaction. A common type of food intolerance is lactose intolerance. People with lactose intolerance lack an enzyme (called lactase) needed to digest the milk sugar (called lactose). They can develop gas, bloating, and abdominal pain when they consume milk products.
Some types of food intolerance can be treated. For example, lactase tablets are available without a prescription to aid those with severe symptoms of lactose intolerance and lactose-free dairy products are available at most supermarkets.
If an individual thinks they may have either food allergy or food intolerance, they should keep a diary of the foods eaten and any symptoms experienced. A food diary can help the doctor establish the correct diagnosis. A doctor can also order simple skin tests or blood tests to determine if an individual is allergic to specific foods. The strategy of dealing with a food allergy is different than dealing with food intolerance.
Foods That Cause Allergies
There are no medications that can cure food allergies. Diligent avoidance of the offending food is the only sure way to prevent a reaction. People with food allergies must thoroughly examine food labels and ask questions about the ingredients of dishes. For example, the label on a breakfast cereal may read, "May contain soy, peanuts, and/or other tree nuts."
To help you spot hidden food triggers, look over this list. See where they lurk in common grocery-store products. Almost any food can trigger an allergy, but these are most common ones:
- Milk (mostly in children)
- Tree nuts (like walnuts and pecans)
- Fish (mostly in adults)
- Shellfish (mostly in adults)
A milk allergy is a reaction to milk proteins like casein. Some people cannot drink cow's milk but are fine with sheep's or goat's milk. Others can't have any type of milk. Common symptoms are severe stomach pain, diarrhea, skin hives, or difficulty breathing.
Remember, lactose intolerance is not a milk allergy, but the inability to digest the sugar in milk (lactose). People who are lactose intolerant may suffer gastrointestinal symptoms such as bloating and gas but won't have the allergy symptoms above.
If you are allergic to cow's milk, read labels carefully. Greek-style yogurt is made with cow's milk, but Greek yogurt is made with goat's milk. Various forms of milk are found in products like cake mixes, instant mashed potatoes, and baked goods including pies. Milk products are also found in Indian dishes -- where ghee (a form of butter) is very common.
In most cases, egg allergies are mild but are caused by even tiny amounts of egg. Sometimes, it's the egg white (albumen) that's the problem; for other people, it's the egg yolk. In rare cases, an egg allergy can trigger anaphylaxis.
While some products clearly list eggs or egg proteins as ingredients, others are less clear. If only tiny amounts of egg are in the product, you won't always see it on the label.
Noodles may contain egg but not list it as an ingredient. Processed meats, like sausages, often have egg hidden in the mix. Bagels, pretzels, and other baked goods get their shiny appearance from egg white -- but it's not mentioned on the package label.
Peanut allergy is one of the most common food allergies and is the leading cause of deadly food allergy reactions. Shaking hands with someone who has handled peanuts, or even smelling peanuts, can produce an allergic reaction in some people. For some people, the reaction is so severe that it causes fatal anaphylaxis.
Peanuts are used in a variety of processed foods like ice cream (as a flavoring), marinades, snack foods, biscuits, baked goods, and candy. Certain ethnic dishes also contain peanuts or peanut oil: African, Chinese, Indonesian, Mexican (enchilada sauce), Thai, and Vietnamese cuisines all contain dishes that use peanuts as an ingredient. Some flavorings are nut-based. Peanuts are also used as a thickener in prepared foods. Many roasted and fried foods (including roasted chicken) contain peanut oil.
If you have a peanut allergy, be careful with other types of nuts. Although peanuts are technically a legume (a bean) that grows underground, you may be allergic to nuts grown on trees -- especially almonds, walnuts, hazelnuts, Brazil nuts, and cashews.
Tree Nut Allergies
If you have a peanut allergy, you likely need to avoid tree nuts, too -- cashews, almonds, pecans, walnuts, hazelnuts, pine nuts, Brazil nuts, and macadamia nuts. Also, be careful with coconut, chestnut, ginkgo nuts, and lychee (lichee) nuts as they are also considered tree nuts. Like peanuts, tree nuts are dangerous because they are hidden in so many foods -- even nonfood products like lotions and shampoos.
When you have an allergic reaction to wheat, it's really intolerance to gluten -- the protein found in wheat, rye, barley, and oats. Wheat is found in many types of baked goods and breads -- from white bread to Indian naan -- and is also found in rye bread. Even gluten-free bread may contain small amounts of wheat.
Gluten intolerance is associated with the disease called "gluten-sensitive enteropathy" or "celiac disease." With celiac disease, your immune system responds abnormally to gluten. Some researchers include celiac disease as a food allergy. Technically, however, the immune response caused by celiac disease is different than the response caused by other food allergies. Symptoms of celiac disease include gas, bloating, diarrhea, weight loss, fatigue, and sometimes vomiting.
Ale, beer, bourbon, and whiskey contain wheat -- and so does wine.
Many medications in tablet form have a wheat binder that isn't listed on the label. If you have a wheat allergy, you need a liquid form or one that uses potato or corn starch.
Soybeans have nearly unlimited uses -- as the main ingredient in soy milk, soy sauce, and soy nuts. Like peanuts and tree nuts, soy hides in a great many food products you would never suspect. Soybean flour is used in many baked goods, like pastries, cakes, biscuits, and breads, as well as ice cream, breakfast cereal, frozen dinners, salad dressings, mayonnaise, and margarine. It's also used in sausages, hamburgers, and other meat products. Even baby food contains soy!
Soy is used so widely in food processing that is very difficult to avoid, but many products do not list "soy" on an ingredient label. For example, there may be soy added to margarine, but you won't find soy listed in the ingredients. You must look for key words like "hydrolyzed protein," "lecithin," "texturizer," "emulsifier," "protein filler," or "extender."
A fish allergy is relatively easy to avoid. When you've had a severe anaphylactic reaction to a type of fish, your health health-care provider will show you how to avoid similar foods that might trigger this reaction. For example, if you have a history of allergy to shrimp, allergy testing will usually show that you are not only allergic to shrimp but also to crab, lobster, and crayfish. This is called "cross-reactivity."
There's also the risk of contamination from other foods. When eating in restaurants, check with the chef. Make sure your fish is not cooked in the same skillet or in the same oil as other food. Also, certain food products (like dressings and sauces) contain small amounts of fish protein that could trigger an allergic reaction.
If you have an allergy to shellfish, you must avoid all types of shellfish. Also, be careful of cross-contamination in restaurants. Some places fry fish in the same skillet or oil as other food.
Shellfish is not often a hidden ingredient in foods. However, there are a few things you should be careful about. Caesar salad dressing and chili may contain fish or shellfish. Some imitation shellfish (Surimi) contain flavoring made from small amounts of real shellfish. Many Asian dishes contain fish and shellfish.
How Are Food Allergies Diagnosed?
By keeping a food diary, your doctor will have a much better starting point to determine the foods that could trigger your allergies.
Your doctor may recommend a food elimination diet in which you may be asked to eliminate one or several potentially allergenic foods to see if the reaction goes away,
Oral food challenges -- exposing the person to the suspected food under medical supervision -- are thought to be helpful as well.
Your doctor may order a radioallergosorbent blood test (RAST) to check the number of antibodies produced by your immune system. Elevated levels of certain types of antibodies can help your doctor identify specific food allergies.
The doctor may also perform an allergy skin test, also called a scratch test, to identify the substances that are causing your allergy symptoms.
Food allergies are caused by immunological reactions to foods, sometimes in individuals or families predisposed to allergies. A number of foods, especially shellfish, milk, eggs, peanuts, and fruit can cause allergic reactions (notably hives, asthma, abdominal symptoms, lightheadedness, and anaphylaxis) in adults or children. When a food allergy is suspected, a medical evaluation is the key to proper management.
It is important to distinguish a true food allergy from other abnormal responses to food, such as food intolerances, which actually are far more common than food allergy. Once the diagnosis of food allergy is made (primarily by the medical history) and the allergen is identified (usually by skin tests), the treatment basically is to avoid the offending food. People with food allergies should work with their physicians and become knowledgeable about allergies and how they are diagnosed and treated.
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