Skip to content

Allergies Health Center

Font Size

Understanding Anaphylaxis -- the Basics

What Is Anaphylaxis?

Anaphylaxis is a sudden, severe allergic reaction. It's a medical emergency.

Most people with allergies never have anaphylaxis. But when it happens, it works like this:

Within minutes or hours of being exposed to your allergy trigger, your body starts a chain reaction that widens your blood vessels, which can lower your blood pressure. You may pass out. You may get hives and swelling, especially around your face and throat. You may have trouble breathing, talking, or swallowing.

What Causes Anaphylaxis?

The most common triggers for anaphylaxis are:

  • Peanuts and tree nuts (particularly almond, walnut, hazel, Brazil, and cashew nuts)
  • Fish and shellfish, especially shrimp and lobster
  • Dairy products
  • Eggs
  • Insect bites and stings, mainly those from wasps, bees, and ants
  • Latex
  • Medications

Sometimes exercise can cause a severe reaction, usually after you eat something you’re allergic to.

Call 911

Call 911 if you even suspect anaphylaxis.

An injection of a drug called epinephrine can delay symptoms. These injections aren’t a cure, though they may give you more time to get treatment -- and that could save your life. The drug quickly narrows your blood vessels, stops swelling in your throat and face, and relaxes the muscles in your lungs to help you breathe.

Because this reaction can happen so fast, always act quickly and take it seriously. Use epinephrine first and then call 911 right away.

WebMD Medical Reference

Reviewed by Luqman Seidu, MD on February 28, 2015

Today on WebMD

man blowing nose
Make these tweaks to your diet, home, and lifestyle.
Allergy capsule
Breathe easier with these products.
cat on couch
Live in harmony with your cat or dog.
Woman sneezing with tissue in meadow
Which ones affect you?

blowing nose
woman with sore throat
lone star tick
Woman blowing nose

Send yourself a link to download the app.

Loading ...

Please wait...

This feature is temporarily unavailable. Please try again later.


Now check your email account on your mobile phone to download your new app.

cat lying on shelf
Allergy prick test
Man sneezing into tissue
Woman holding feather duster up to face, twitching