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Quick Facts

Anaphylactic Reactions

By The Manual's Editorial Staff,

What are anaphylactic reactions?

Anaphylactic reactions (sometimes called “anaphylaxis”) are the most serious, sudden, and life-threatening allergic reactions. You develop severe symptoms such as an itchy rash over your entire body, a swollen throat, and trouble breathing. You might pass out. If the allergic reaction isn't treated, it can be deadly.

You can have an anaphylactic reaction after you touch or eat something you’re allergic to (an allergen).

  • After you have an anaphylactic reaction to something, you’ll most likely have another if you come into contact with that allergen again

  • Symptoms of an anaphylactic reaction usually start within 15 minutes

  • To prevent an anaphylactic reaction, avoid the allergen and always carry a shot of epinephrine and antihistamine pills with you

Go to the emergency room if you have an anaphylactic reaction.

What causes an anaphylactic reaction?

Anything you’re allergic to can cause an anaphylactic reaction. The most common causes include:

  • Medicine, such as penicillin

  • Insect stings

  • Foods, particularly eggs, seafood, and nuts

  • Latex (a type of rubber in some gloves and balloons)

Usually you don't have an anaphylactic reaction the first time you're exposed to an allergen. Your body has to be exposed to something to become allergic. However, many people do not recall a first exposure.

What are the symptoms of an anaphylactic reaction?

Anaphylactic reactions usually come on quickly, within 15 minutes of being around the allergen.

Symptoms may be different for each person, but usually you have the same symptoms each time. These symptoms can include:

  • Itching all over, with red patches on your skin (hives)

  • Swollen eyes, lips, tongue, and throat

  • Wheezing and trouble breathing

  • Belly cramps, feeling sick to your stomach, and throwing up

  • Dizziness and fainting because of a drop in your blood pressure

If you don't get help, you may stop breathing, have a seizure, or pass out. Anaphylactic reactions are life-threatening.

How can doctors tell if I have an anaphylactic reaction?

Doctors can tell right away based on your symptoms and by examining you.

Sometimes, you'll know what caused your anaphylactic reaction. For example, you might have accidentally eaten something you're allergic to, such as a cookie that you didn't know had nuts in it. Other times it is hard for doctors to tell what caused the reaction.

How do doctors treat anaphylactic reactions?

Doctors will give you a shot of epinephrine (medicine to treat a serious allergic reaction). If you still have trouble breathing, doctors may put a breathing tube in your nose or mouth and give you oxygen.

Sometimes they will also give you:

  • Medicine to raise your blood pressure

  • Fluids through your vein

  • Medicine to open your airway and help you breathe

  • Medicines to reduce swelling (antihistamines)

How can I prevent an anaphylactic reaction?

  • Avoid the things you’re allergic to

  • Ask you doctor about allergy shots if you’re allergic to something that's hard to avoid, like insect stings

  • Always carry a shot of epinephrine and antihistamine pills with you

Your doctor can write you a prescription for a syringe full of epinephrine. Carry the syringe with you at all times. If you’re around your allergen or start to have an anaphylactic reaction, give yourself a shot of epinephrine and take an antihistamine pill. Then go to a hospital emergency room in case you need more treatment.

Wear a medical alert bracelet that lists your allergies in case you pass out and need medical help.