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    Food Allergies

    A food allergy happens when your immune system reacts to something that you’ve eaten.

    When you eat something you are allergic to, your body makes antibodies. Over time, sometimes as soon as the second time you eat it, the antibodies spring into action, starting a process that includes the release of lots of histamine to fight what it believes is invading your body.

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    Histamine is a powerful chemical that can affect your respiratory system, digestive tract, skin, and heart and blood vessels.

    What Are the Symptoms of a Food Allergy?

    Symptoms may appear almost immediately or up to 2 hours after you've eaten the food. Symptoms can include:

    Severe reactions, called anaphylaxis, can result in death.

    You can get a rash in areas that come in contact with foods. Some people are so sensitive to food allergens that the odor of that particular food can cause a reaction.

    Which Foods Most Often Cause Allergic Reactions?

    The most common food allergies are reactions to:

    • Milk
    • Eggs
    • Peanuts
    • Seafood
    • Tree nuts (such as walnuts, pecans, almonds, pine nuts, and Brazil nuts)

    How Are Food Allergies Diagnosed?

    If you keep a food diary, your doctor will have a better starting point to figure out foods that could trigger your allergies.

    Your doctor may suggest a food elimination diet. If he does, you may be asked to eliminate one or several 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. These are usually done after the elimination diet.

    Your doctor may do a radioallergosorbent blood test (he may call it a RAST) to see how many antibodies your immune system makes. High levels of some antibodies can help your doctor spot specific food allergies.

    You may also get an allergy skin test, also called a scratch test.

    Some food allergies are very mild, and in difficult-to-diagnose cases, a promising new antibody test may help. More research is needed. Also, there are now genetic tests, especially for gluten and celiac (wheat, barley, rye, and some oats).

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