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    Do I Have Chronic Allergies?

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    Why Allergies Happen continued...

    Your odds of developing an allergy start in your genes. While specific allergies are not inherited, a tendency toward having allergies is.

    Children with one allergic parent have a 33% chance of developing allergies. With two allergic parents, it's a 70% chance.

    Even so, the circumstances have to be just right for something to trigger an allergic reaction.

    Other things may also be involved. For instance, if you come into contact with an allergen when you're weak, such as after a viral infection -- you might be more likely to develop an allergy to it.

    How an Allergy Starts

    It begins with exposure. Even if you've been around a trigger (or “allergen,” as your doctor calls it) many times before with no trouble, your body may suddenly see it as an invader. If this happens, your immune system studies the allergen and makes antibodies against it, in case the same situation happens again.

    Then, the next time you come across that allergen, your immune system takes action. The antibodies recognize it and turn on special cells called mast cells.

    The mast cells burst open, releasing chemicals such as histamine that cause symptoms such as swelling. Swelling in your nasal passages might cause a runny nose. Swelling in the airways could cause asthma symptoms.

    Keep in mind that the amount of exposure can make a difference. If you're allergic to strawberries, you may have been able to eat one or two without symptoms. But once you eat three or four, you suddenly break out in hives. There's a tipping point -- or threshold -- for people with allergies. You can handle some exposure, but too much launches an immune system attack.

    The problem is that you can’t predict how you’ll recover. So if you have a food allergy, you should avoid your trigger foods completely.

    WebMD Medical Reference

    Reviewed by William Blahd, MD on April 13, 2016
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