Why Are You Allergic: Allergies
Content provided by the Faculty of the Harvard Medical School
Why are you allergic?
Allergic reactions are inappropriate, overblown responses mounted by the body’s immune system against a harmless substance — take ragweed pollen, for example. Ragweed pollen is not poisonous, infectious, or in any way harmful to humans. But in some people it triggers an attack by immune system cells that takes the form of an allergic reaction. When this happens, the ragweed pollen — or any offending substance — is called an allergen.
You develop allergies for two reasons: First, you are genetically predisposed to be allergic; second, factors in your environment, especially when you are young, make you more susceptible. Most allergies are caused by some combination of genetics and environment.
| Last updated: | August 21, 2006 |
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| Reviewed By: | Faculty of Harvard Medical School |
Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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