Anaphylaxis is a severe, life-threatening allergic reaction that affects organ systems throughout the body. It occurs when the immune system becomes sensitized to an allergen, such as a food, drug, or insect venom. Upon re-exposure to the allergen, the immune system overreacts, releasing cascades of histamine and other substances that can cause contraction of the intestinal smooth muscles, skin reactions, constriction of the airways, and a precipitous drop in blood pressure that may lead to shock. Immediate medical attention is essential; severe cases may prove fatal even with treatment.

What Causes Anaphylaxis?

  • An insect sting
  • Ingestion of a food or food additive such as peanuts, tree nuts (e.g. almonds, walnuts, cashews, Brazil nuts), fish, sesame, shellfish, eggs and dairy products. Peanuts are the most common cause of food-induced anaphylaxis.
  • Latex or rubber (e.g., found in surgical gloves, medical supplies and household products)
  • Medications, such as penicillin and aspirin, and injection of a drug, vaccine, or chemical used in a diagnostic procedure can cause anaphylaxis. Penicillin is the most common cause of drug-induced anaphylaxis.
  • Rarely, symptoms occur without apparent exposure to a known cause.

Symptoms of Anaphylaxis

  • Itching is often the first symptom
  • Generalized flushing of the skin (redness, sweating, swelling)
  • Hives
  • Swelling of the eyes, lips, and tongue
  • Weakness or faintness
  • Tightening in the chest or throat; wheezing; shortness of breath
  • Trouble swallowing or speaking
  • Abnormal heart rate
  • Severe asthma
  • Profuse sweating
  • Palpitations
  • Sudden, intense distress; feelings of impending doom
  • Stomach cramps, abdominal pain, nausea and vomiting, or diarrhea
  • Bluish tinge (cyanosis) to the skin, lips, and nail beds due to oxygen insufficiency
  • Collapse and unconsciousness


  • Avoid allergens that have caused an adverse reaction in the past.
  • If you are allergic to insect stings, wear protective clothing and insect repellent when outside.
  • If you have food allergies, avoid foods to which you are allergic. Even small amounts accidentally mixed into your food can cause a reaction. Always read the ingredient list on any packaged foods before eating.
  • People who have previously had a severe allergic reaction should wear a Medic-Alert bracelet and get a prescription for epinephrine (adrenaline), which halts the allergic reaction and should be carried at all times. An easy-to-use form is the Epi-pen, a spring-loaded device that automatically injects a dose of epinephrine when pressed against the skin (usually the leg). The drug does not substitute for necessary medical treatment but does buy valuable time until help can be found.
  • Consult your doctor if you need desensitization shots.
  • Keep an emergency anaphylaxis kit with you at all times. Make sure your family members and friends know how to use it.

In March 2013, the U.S. Food and Drug Administration (FDA) recommended manufacturers of FDA-regulated medical products discontinue using terms like "latex-free" or "does not contain latex." According to the FDA, there aren't reliable tests to determine if a product contains nature rubber latex proteins that can cause allergic reactions, and "latex-free" labeling may be dangerously misleading. Instead, a statement such as "not made with natural rubber latex" may be more accurate on products like adhesive bandages, condoms, medical gloves, catheters, sanitary napkins, crutches and blood-pressure cuffs.


Diagnosis is indicated by the sudden onset of characteristic symptoms, usually within five minutes to one hour following exposure to a suspected allergen. Since anaphylaxis is an emergency, immediate treatment supersedes the need for further confirmatory procedures. Blood, urine or allergy tests for the specific allergen may be done after the patient has stabilized.

How to Treat Anaphylaxis

  • Immediate medical treatment is necessary. An injection of the adrenal hormone epinephrine (adrenaline) is necessary to counteract the effect of histamine throughout the body. Doses may need to be repeated every 10 to 20 minutes until the reaction ceases.
  • Inhalers such as albuterol improve breathing.
  • If life-threatening breathing obstruction has occurred due to swelling of the larynx, a tube may be placed through the mouth or nose to aid in breathing; in very serious cases a tracheostomy (insertion of a breathing tube through a surgical opening in the throat) may be needed.
  • Intravenous fluids containing blood pressure-raising agents are administered if shock occurs.
  • Antihistamines (such as diphenhydramine) or corticosteroids (such as prednisone) may be used after the initial crisis has passed to prevent return of symptoms.

When to Call a Doctor

EMERGENCY An anaphylactic reaction requires immediate medical attention. Call an ambulance or get to an emergency room right away.


Johns Hopkins Symptoms and Remedies: The Complete Home Medical Reference

Simeon Margolis, M.D., Ph.D., Medical Editor

Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 24 Aug 2011

Last Modified: 23 Dec 2014