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How do antihistamines work to treat allergies?

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When you are exposed to an allergen -- for example ragweed pollen -- it triggers your immune system. People with allergies demonstrate an exaggerated immune response. Immune system cells known as "mast cells" release a substance called histamine, which attaches to receptors in blood vessels, causing them to enlarge. Histamine also binds to other receptors causing redness, swelling, itching, and changes in secretions. By blocking histamine and keeping it from binding to receptors, antihistamines prevent these symptoms.

From: Allergy Medications WebMD Medical Reference

SOURCE: 

American Academy of Allergy, Asthma and Immunology.

FDA. News release.

Sanofi-aventis U.S. News release. 

UpToDate.com. “Patient information: Allergic rhinitis (seasonal allergies) (Beyond the Basics).”

Reviewed by Arefa Cassoobhoy on May 3, 2017

SOURCE: 

American Academy of Allergy, Asthma and Immunology.

FDA. News release.

Sanofi-aventis U.S. News release. 

UpToDate.com. “Patient information: Allergic rhinitis (seasonal allergies) (Beyond the Basics).”

Reviewed by Arefa Cassoobhoy on May 3, 2017

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What are the side effects of antihistamines for allergies?

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