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What Is Anaphylaxis?

John, a 32-year-old salesman, came down with strep throat. His doctor prescribed penicillin to treat it. An hour after taking the first pill, John developed a red, itchy rash, felt dizzy and passed out. His wife found him and he was taken to an emergency room. He was treated successfully with shots and fluids.

A bee stung 15-year-old Terry. Within five minutes she felt hot and flushed and began to have difficulty breathing. A few minutes later, she felt very dizzy and nauseated. She was promptly taken to her family doctor, who successfully treated her with shots.

Several times, Robert, a 42-year-old construction worker, had a raised and itchy rash, nausea, vomiting and diarrhea, and lost consciousness. This has happened 12 times in the past two years. None of these events were related to taking medication, eating a certain food or getting bitten by an insect. Robert carries a self-injectable epinephrine for self-care at the first sign of symptoms. In most cases, this prevents attacks.

All of these people have experienced anaphylaxis. It is a life-threatening allergic reaction that causes breathing problems and loss of consciousness, among other symptoms. It usually occurs within minutes after contact with an allergen—a substance that causes an allergic reaction. Without speedy treatment, this reaction can cause death.

What Are the Symptoms?

When anaphylaxis happens, it affects the whole body. Blood vessels widen so much that blood pressure plummets. Symptoms include flushed skin, rash, swelling of tissues such as lips or joints, stuffy nose, sweating, paleness, panting, nausea, abdominal cramps, rapid pulse, faintness, confusion, wheezing, convulsions and passing out.

Other symptoms include itching of the mouth and throat, hoarseness, cramping of the uterus, and feeling the need to urinate.

What Causes Anaphylaxis?

People who experience anaphylactic reactions have excessive amounts of immunoglobulin E (IgE) antibodies to allergens in their blood. When the allergen is ingested, injected by an insect or comes in contact with the skin as with latex, the antibodies trigger the release of chemicals, particularly histamines, which cause the anaphylaxis, a life-threatening reaction.

For some substances, antibodies may not be present in the blood. The substances themselves cause the symptoms. This is called an anaphylactoid reaction. Medications, insect stings, foods and latex most often cause anaphylaxis and anaphylactoid reactions.

However, some people like Robert, the 42-year-old construction worker, seem to have a reaction without any known exposure to common allergens. This is known as idiopathic anaphylaxis. In other people, a number of substances are common causes of anaphylaxis or anaphylactoid reactions:

  • Medications are the leading cause. Anaphylactic deaths from taking medications are well documented. Common culprits are penicillin and other antibiotics, aspirin and aspirin-related products, muscle relaxants, seizure medications and dyes used during certain procedures such as nuclear imaging. People with allergies or asthma are more likely to have an anaphylactic reaction to shots.

  • Foods that most commonly cause the reaction in children are eggs, peanuts, wheat and milk. In adults, the causes most often are shellfish, tree nuts, peanuts and other legumes.

  • Stings from insects such as bees, wasps, yellow jackets, hornets and fire ants can cause anaphylaxis. Bites from the "kissing bug" and deer fly also cause the reaction. Experts estimate that at least 40 deaths per year are caused by anaphylaxis to insect stings.

  • Intense exercise, particularly in hot weather, can bring on anaphylaxis. Sometimes this only occurs with exercise after eating celery, shellfish, wheat, peaches or other specific foods to which the person is allergic.

How Is It Diagnosed?

Skin tests can confirm sensitivity to certain allergens that can cause anaphylaxis. The skin is pricked or scratched with an extract of the suspected allergen. Redness and swelling of the area indicates an allergic response.

For those with severe reactions, though, skin testing can cause anaphylaxis. A blood test (RAST or radioallergosorbent release test) is then ordered to look for IgE antibodies to allergens. This test takes longer and costs more, but is safer.

What Can I Do to Prevent Anaphylaxis?

  • Make sure your doctors know the names of any medications you are allergic to, and what symptoms you have when you are exposed to them.

  • Make sure your doctors know the names of every medication you take. Some classes of medications like beta adrenergic blocking agents can worsen an anaphylactic reaction if you should have one.

  • Be familiar with both the generic name and all trade names of medications that cause you to have an anaphylactoid reaction. And be aware of ingredients in a combination product. Read drug information carefully.

  • Become familiar with medications that might cause a cross-reaction. For example, cephalosporin antibiotics may cross-react with penicillin. If you have had an anaphylactic reaction to penicillin, be very cautious about taking these antibiotics. If you are allergic to aspirin, beware of a similar reaction to other pain relievers called nonsteroidal anti-inflammatory medications (such as Motrin, Advil, Nuprin, or Aleve).

  • When possible, take oral medications rather than a shot. This lessens severity of the reaction. If your doctor gives you a shot, wait at least 20 minutes before leaving. If you do have a reaction, you can get prompt treatment.

  • If you have a food allergy, be careful about everything you eat. Check ingredients on all food labels. Ask restaurant staff how food is prepared. People sensitive to a certain food like shellfish or peanuts may have a reaction to other foods if they were prepared in a dish or with utensils that were used to handle the food to which they are allergic. (See the Asthma and Allergy Answers fact sheet on, "What is a Food Allergy?")

  • If you react to insect stings or exercise, talk to your doctor about how to avoid these reactions.

  • Wear a Medic Alert bracelet or necklace to let others know of your allergy in an emergency. Also keep a card in your wallet or purse that explains your allergy.

  • Carry your emergency epinephrine with you at all times.

What About Treatment?

  • Always carry injectable epinephrine, such as Auvi-Q, EpiPen or others. Promptly inject the medication at the first sign of an anaphylactic reaction. 

  • Seek medical care immediately even if you feel better because symptoms can recur in a few hours.

  • If you take a beta blocker or an ace inhibitor for heart disease, you may have a severe bronchospasm along with anaphylaxis. You may need an inhaled beta 2-selective bronchodilator besides epinephrine. Oxygen may be needed. Prolonged treatment with corticosteroids may also be required.


Also learn more about anaphylaxis from the American College of Asthma, Allergy & Immunology (ACAAI).

SOURCE: This information should not substitute for seeking responsible, professional medical care. First created 1995; updated 2011.
© Asthma and Allergy Foundation of America (AAFA) Editorial Board

© Asthma and Allergy Foundation of America
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