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Anaphylaxis is a serious allergic reaction that involves more than one organ system (for example, skin, respiratory tract, and/or gastrointestinal tract). It can begin very rapidly, and symptoms may be severe or life-threatening.

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The most common causes of anaphylaxis are reactions to foods (especially peanuts), medications, and stinging insects. Other potential triggers include exercise and exposure to latex. Sometimes, anaphylaxis occurs without an identifiable trigger. This is called idiopathic anaphylaxis.

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Anaphylaxis includes a wide range of symptoms that can occur in many combinations and may be difficult to recognize. Some symptoms are not life-threatening, but the most severe ones restrict breathing and blood circulation.

Many of the body’s organs can be affected:

  • Skin—itching, hives, redness, swelling
  • Nose—sneezing, stuffy nose, runny nose
  • Mouth—itching, swelling of the lips or tongue
  • Throat—itching, tightness, difficulty swallowing, swelling of the back of the throat
  • Chest—shortness of breath, cough, wheeze, chest pain, tightness
  • Heart—weak pulse, passing out, shock
  • Gastrointestinal (GI) tract—vomiting, diarrhea, cramps
  • Nervous system—dizziness or fainting

How soon after exposure will symptoms occur?

Symptoms can begin within minutes to hours after exposure to the allergen. Sometimes the symptoms go away, only to return anywhere from 8 to 72 hours later. When you begin to experience symptoms, seek immediate medical attention because anaphylaxis can be life-threatening.

How do you know if a person is having an anaphylactic reaction?

Anaphylaxis is likely if a person experiences two or more of the following symptoms within minutes to several hours after exposure to an allergen:

  • Hives, itchiness, or redness all over the body and swelling of the lips, tongue, or back of the throat
  • Trouble breathing
  • Severe GI symptoms such as abdominal cramps, diarrhea, or vomiting
  • Dizziness or fainting (signs of a drop in blood pressure)

If you are experiencing symptoms of anaphylaxis, seek immediate treatment and tell your healthcare professional if you have a history of allergic reactions.

Can anaphylaxis be predicted?

Anaphylaxis caused by an allergic reaction is highly unpredictable. The severity of a one attack does not predict the severity of subsequent attacks. Any anaphylactic reaction can become dangerous quickly and must be evaluated immediately by a healthcare professional.

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An anaphylactic reaction can occur as any of the following:

  • A single reaction that occurs immediately after exposure to the allergen and gets better with or without treatment within minutes to hours. Symptoms do not recur later in relation to that episode.
  • A double reaction. The first reaction occurs within minutes or hours. The initial symptoms seem to go away but later reappear in a second reaction, which typically occurs 8 to 72 hours after the first reaction.
  • A single, long-lasting reaction that continues for hours or days.

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If you or someone you know is having an anaphylactic episode, health experts advise using an auto-injector, if available, to inject epinephrine  into the thigh muscle, and calling 9-1-1 if you are not in a hospital. (Epinephrine is a hormone that increases heart rate, constricts the blood vessels, and opens the airways.) If you are in a hospital, summon a resuscitation team.

If epinephrine is not given promptly, rapid decline and death could occur within 30 to 60 minutes. Epinephrine acts immediately but does not last long in the body, so it may be necessary to give repeat doses.

After epinephrine has been given, the patient can be placed in a reclining position with feet elevated to help restore normal blood flow.

A healthcare professional also may give the patient any of the following secondary treatments:

  • Medicines to open the airways
  • Antihistamines to relieve itching and hives
  • Corticosteroids (a class of drugs used to treat inflammatory diseases) to prevent prolonged inflammation and long-lasting reactions
  • Additional medicines to constrict blood vessels and increase heart rate
  • Supplemental oxygen therapy
  • Intravenous fluids

Conditions such as asthma, chronic lung disease, and cardiovascular disease may increase the risk of death from anaphylaxis. Medicines such as those that treat high blood pressure also may worsen symptom severity and limit response to treatment.

Antihistamines should be used only as a secondary treatment. Giving antihistamines instead of epinephrine may increase the risk of a life-threatening allergic reaction.

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Before leaving emergency medical care, your healthcare professional should provide the following:

  • An epinephrine auto-injector or a prescription for two doses and training on how to use the auto-injector
  • A follow-up appointment or an appointment with a clinical specialist such as an allergist or immunologist
  • Information on where to get medical identification jewelry or an anaphylaxis wallet card that alerts others of the allergy
  • Education about allergen avoidance, recognizing the symptoms of anaphylaxis, and giving epinephrine
  • An anaphylaxis emergency action plan (Download the PDF of a sample plan from the American Academy of Allergy, Asthma & Immunology.)

If you or someone you know has a history of severe allergic reactions or anaphylaxis, your healthcare professional should remember to keep you S.A.F.E.

  • Seek support: Your healthcare professional should tell you the following:
    • Anaphylaxis is a life-threatening condition.
    • The symptoms of the current episode may occur again (sometimes up to three days later).
    • You are at risk for anaphylaxis in the future.
    • At the first sign of symptoms, give yourself epinephrine and then immediately call an ambulance or have someone else take you to the nearest emergency facility.
  • Allergen identification and avoidance: Before you leave the hospital, your healthcare professional should have done the following:
    • Made efforts to identify the allergen by taking your medical history
    • Explained the importance of getting additional testing to confirm what triggered the reaction, so you can successfully avoid it in the future
  • Follow-up with specialty care: Your healthcare professional should encourage you to consult a specialist for an allergy evaluation.
  • Epinephrine for emergencies: Your healthcare professional should give you the following:
    • An epinephrine auto-injector or a prescription and training on how to use an auto-injector
    • Advice to routinely check the expiration date of the auto-injector

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NIAID-funded research focuses on anaphylaxis induced by food allergens. NIAID supports basic research in allergy and immunology to understand how, in certain people, foods elicit allergic reactions that can range from mild to severe. NIAID also conducts clinical trials of therapies that may alter the body’s immune response so that it no longer triggers an allergic response to food. Learn more about NIAID-funded research programs in food allergy.

The Laboratory of Allergic Diseases (LAD) supports basic, translational, and clinical research on anaphylaxis. Researchers in LAD seek to better understand the various immune system components that are involved in anaphylaxis; identify molecular events that cause and characterize anaphylactic reactions to understand their triggers; and discover diagnostic markers or reveal targets for new therapies to help prevent and treat life-threatening allergic reactions. Read more about LAD.

In December 2010, comprehensive guidelines for the diagnosis and management of food allergy were published. The guidelines provide healthcare professionals with recommendations on the best ways to identify food allergy and help people manage this condition, even its most severe forms. NIAID helped lead the guidelines effort, working with 34 professional organizations, patient advocacy groups, and federal agencies. Read about the Guidelines for the Diagnosis and Management of Food Allergy in the United States.

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Last Updated April 23, 2015