A severe allergic reaction (anaphylaxis) is your bodyâ€™s reaction to a substance that is normally harmless. With allergies, your body sees the substance as harmful or foreign and your immune system reacts to the substance. Substances that can cause an allergic reaction are called allergens.
A severe allergic reaction is life threatening.
What is the cause?
Your immune system is your body’s natural defense against bacteria, viruses, and other foreign substances. Before you can have a reaction to a particular substance, your immune system must first be sensitive to it. Usually this means your body has to have been exposed to the substance at least once before. Once it is sensitive to it, your body will react every time you have contact with the substance.
A severe allergic reaction is caused by your whole body overreacting to a substance you are allergic to. The reaction causes blood vessel walls to relax and leak fluid into body tissue. This can cause swelling in your airway and trouble breathing. It can also make your blood pressure drop suddenly and cause you to go into shock.
A severe allergic reaction may be caused by many things. Common causes include:
Food such as nuts, peanuts, shellfish, or food additives
Insect stings and bites
Vaccines or allergy shots
Latex (a liquid from rubber trees that is used in many products, like gloves and toys)
Anesthetics (medicine given to prevent pain during surgery)
In rare cases, pollens, dust, perfume, chemicals, animal dander (dried skin flakes) or other substances in the air (including the smoke from burning poison ivy, poison oak, or poison sumac)
What are the symptoms?
Symptoms usually start within minutes to an hour or two after contact with the substance. Symptoms may include:
Severe trouble breathing, including wheezing
Swelling of your lips, tongue, or throat
Hives (raised, red, itchy areas on your skin)
Pale, cool, damp skin
Fast or pounding heartbeat
Nausea and vomiting
Feeling intense fear that something terrible is about to happen
Drowsiness, confusion, or fainting
How is it diagnosed?
Your healthcare provider will ask about your symptoms and medical history and examine you. Tests may include:
A skin prick test, which uses a drop of allergen extract (liquid) put under your skin using a needle
Elimination diet, which means you avoid eating certain foods for a few weeks to see if allergy symptoms go away
Food challenge test, which is eating food that is a possible allergen to see if you have a reaction. This test is done only by a healthcare provider who is ready to treat you if you have a serious reaction to the food.
How is it treated?
A severe allergic reaction is life-threatening and usually needs to be treated with epinephrine. Epinephrine relaxes the muscles in your airways and throughout your body. It is usually given as a shot. You may need more than one shot to decrease your symptoms.
If you are known to have severe allergic reactions, your provider may want you to carry an emergency kit. You or someone with you can give you the epinephrine shot. Whether or not you have epinephrine, call 911 or your local emergency services right away for all severe allergic reactions.
Several other kinds of medicines may be used to treat a severe allergic reaction:
Antihistamines to block the effect of histamine and help reduce your symptoms. Histamine is a chemical your body makes when you have an allergic reaction. Do not give antihistamines to children under the age of 4. If your child is between the ages of 4 and 6, ask your healthcare provider before giving antihistamines.
Steroids help to lessen irritation and swelling in your body. By lessening the swelling, you will have fewer symptoms and be able to breathe better.
Bronchodilators to open your airways and make it easier to breathe.
You may need to stay in the emergency room or hospital to make sure that your blood pressure and heartbeat go back to normal. You will also be watched to make sure that the allergy symptoms donâ€™t come back as the effect of the medicines wears off.
If someone else is having a severe allergic reaction:
Call 911 or local emergency services for help right away.
If you know CPR, check for breathing and a pulse and start CPR if necessary.
Turn the person on their side if they start to vomit.
Try to remove what is causing the reaction, such as a stinger from a bee or food in the mouth. Save the item for healthcare providers if you can.
See if the person is wearing a medical ID bracelet or necklace that says what kind of allergy they have.
How can I take care of myself and prevent a severe allergic reaction?
To prevent severe allergic reactions, your healthcare provider may recommend immunotherapy. This treatment includes shots or pills containing small amounts of the substances you are allergic to. It may be recommended if your allergy symptoms cannot be controlled with medicine. It may take several months of treatment before your symptoms get better. Follow the full course of treatment prescribed by your healthcare provider. In addition:
Learn what substances cause you to have an allergic reaction and avoid those substances. If you have drug or food allergies, always check labels before taking any prescription or nonprescription medicines or eating any foods. Always read labels and ask about ingredients in restaurant or cafeteria foods.
Tell all pharmacists, healthcare providers, and dentists who treat you about any allergies you have and your reactions. Some medicines contain ingredients that might cause an allergic reaction.
If you were prescribed an emergency kit, carry it at all times. Use it as directed by your provider. Check the expiration date for the medicine and replace it as needed to make sure it will work.
Wear a medical alert bracelet or necklace that warns of your allergy and tells what to do in case of an emergency. Teach family members and coworkers how to help you if you have a severe reaction.
Ask your provider:
How and when you will hear your test results
If there are activities you should avoid and when you can return to your normal activities
How to take care of yourself at home
What symptoms or problems you should watch for and what to do if you have them
Make sure you know when you should come back for a checkup. Keep all appointments for provider visits or tests.
Adult Advisor 2015.1 published by RelayHealth. Last modified: 2014-10-23 Last reviewed: 2014-09-18
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Allergic Reaction, Severe (Anaphylaxis): References
Arnold, J.J., Williams, P.M. (2011). Anaphylaxis: Recognition and Management. American Family Physician, 84(10): 1111-1118. Retrieved 09/16/14.
American College of Allergy, Asthma and Immunology.(2010). Anaphylaxis. Accessed July 18, 2014, from