The Facts

Anaphylaxis is a medical emergency. Though rare, this serious type of allergic reaction occurs after a person is exposed to an allergen (a substance they are allergic to), such as certain foods, medications, or insect stings.

The body's immune system quickly reacts, causing swelling of the face and throat, difficulty breathing, dangerously low blood pressure, and leaky blood vessels. These effects can lead to shock. If not treated quickly, anaphylaxis can be fatal.

Avoiding the allergen and knowing what to do if you are exposed are the keys to managing the problem.


Just about any substance can bring on an anaphylactic reaction. But anaphylaxis is most commonly caused by:

  • allergy shots
  • blood products
  • foods such as peanuts, tree nuts, shellfish, eggs, fish, sesame, soy, milk, and wheat
  • insect bites or stings
  • latex (a type of natural rubber found in certain medical supplies)
  • medications such as antibiotics, vaccines, anti-inflammatories and painkillers, and dyes used for CT or MRI scans

Sometimes, the cause for the anaphylaxis is never found. The medical term for this is idiopathic anaphylaxis.

When a person with an anaphylactic allergy is exposed to an allergen, their immune system goes into overdrive. The substances the body produces (e.g., histamine) are intended to protect the body from a foreign invader, but they overreact, causing the throat to swell up and the blood vessels to leak fluid. This leads to the symptoms of anaphylaxis and can be life-threatening.

People with asthma, seasonal allergies, or eczema are at a higher risk of anaphylaxis. Although anaphylaxis rarely occurs, it can happen at any age. Race and geographic location do not affect the risk of anaphylaxis.

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The contents of this health site are for informational purposes only. Always seek the advice of your physician or other qualified healthcare provider regarding any questions you may have about a medical condition.

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