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    What Is Anaphylaxis?

    This serious, sometimes life-threatening allergic response is marked by swelling, hives, lowered blood pressure, and dilated blood vessels. In severe cases, you could go into shock. If anaphylactic shock isn't treated immediately, it can be fatal.

    This condition starts in your immune system. Your body creates a protein (you might hear it called an antibody) called immunoglobulin E or IgE to fight allergens. It kicks off an over-the-top reaction to something that should be harmless, like certain foods.

    Your body may not react the first time you come across this substance, but it could produce antibodies later on. When you come in contact with it again, the allergen binds to these antibodies, and your body churns out more symptom-causing chemicals called histamines. That brings on the anaphylaxis.

    What Are the Symptoms?

    It might begin with severe itching of the eyes or face. Within minutes it could get more serious. You could find it hard to swallow or breathe. It can also affect your stomach -- you might have belly pain, cramps, vomiting, or get diarrhea. Your skin could be involved too, with hives (itchy red welts), and angioedema, a swelling that’s like hives but shows up under your skin.

    What Triggers It?

    Food is most often to blame. Nuts, shellfish (shrimp, lobster), dairy products, egg whites, and sesame seeds are common triggers. So are wasp or bee stings.

    Sometimes exercise can cause it, if you’re active after you eat a trigger food.

    Some medications are also on the list.

    Pollens and other allergens you breathe in rarely cause anaphylaxis.

    Some substances can cause reactions -- called anaphylactoid reactions -- that are similar to and just as serious as anaphylaxis, but don’t involve IgE antibodies. The most common triggers:

    How Is It Diagnosed?

    The symptoms are the clue. If you have a history of allergic reactions, you’re more likely to have severe problem in the future. Skin tests may help your doctor figure out the root cause.