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Patient education: Anaphylaxis symptoms and diagnosis (Beyond the Basics)

John M Kelso, MD
Section Editor
Bruce S Bochner, MD
Deputy Editor
Anna M Feldweg, MD
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Anaphylaxis is a potentially deadly allergic reaction that is rapid in onset. It is most often triggered by foods, medications, and insect stings. There are many other possible triggers.

Anaphylaxis is an unpredictable condition. Many people who experience it have known allergies, and some people have had one or more allergic reactions previously. Others, who are not even aware that they have an allergy, can suddenly experience severe anaphylaxis. Even the first episode of anaphylaxis can be fatal.

The severity of an anaphylactic episode can be minimized by recognizing the symptoms early, having proper medication available for self-treatment, and seeking emergency medical care promptly. This topic reviews the symptoms and diagnosis of anaphylaxis. Treatment and prevention of anaphylaxis and how to use an epinephrine autoinjector are discussed separately. (See "Patient education: Anaphylaxis treatment and prevention of recurrences (Beyond the Basics)" and "Patient education: Use of an epinephrine autoinjector (Beyond the Basics)".)


Symptoms of anaphylaxis generally begin within minutes to one hour or so after exposure to a trigger.

The most common symptoms of anaphylaxis are hives (urticaria) and swelling of the skin (angioedema), which occur in 80 to 90 percent of reactions. Respiratory symptoms occur in about 70 percent of reactions and are especially common in people who also have asthma or another chronic respiratory disease. Extremely low blood pressure causing lightheadedness, dizziness, blurred vision, or loss of consciousness (passing out) occurs in up to about 70 percent of reactions.

Anaphylaxis can cause symptoms throughout the body:

Skin – Itching, flushing, hives (urticaria), swelling (angioedema)

Eyes – Itching, tearing, redness, swelling of the skin around the eyes

Nose and mouth – Sneezing, runny nose, nasal congestion, swelling of the tongue, metallic taste

Lungs and throat – Difficulty getting air in or out, repeated coughing, chest tightness, wheezing or other sounds of labored breathing, increased mucus production, throat swelling or itching, hoarseness, change in voice, sensation of choking

Heart and circulation – Dizziness; weakness; fainting; rapid, slow, or irregular heart rate; low blood pressure

Digestive system – Nausea, vomiting, abdominal cramps, diarrhea

Nervous system – Anxiety, confusion, sense of impending doom

A severe form of anaphylaxis causes sudden collapse without other obvious symptoms, such as hives or flushing. This form of anaphylaxis occurs most commonly after a person is given a medication into a vein or is stung by an insect.

Up to 20 percent of people with anaphylaxis have biphasic (two-phase) anaphylaxis, in which symptoms resolve and then recur without further exposure to the trigger. This can occur up to eight hours after the initial symptoms and sometimes longer.

Rarely, anaphylaxis can be protracted and last for hours or several days despite treatment.


The trigger for a person's anaphylaxis may be obvious or it may be difficult to identify.

Common anaphylaxis triggers can include:

Foods – In children, hen's eggs, cow's milk, peanuts, tree nuts, fish, wheat, and soy are the most common food triggers.

In teens and adults, peanuts, tree nuts, fish, and crustaceans (shellfish such as shrimp) are the most common triggers.

Any food, including fruits, vegetables, seeds, and some spices and food additives, can cause anaphylaxis.

Medications, such as antibiotics (penicillins and cephalosporins) and analgesics (aspirin, ibuprofen).

Venom from insects, including bees, yellow jackets, wasps, hornets, and fire ants.

Latex from natural rubber, found in some latex gloves, balloons, condoms, sports equipment, and medical supplies.

Allergen immunotherapy ("allergy shots"), such as those given for the treatment of allergic rhinitis (hay fever).

Exercise, either by itself or after food ingestion (eg, wheat, celery, shrimp, or other food) or after medication ingestion (eg, aspirin, ibuprofen).

Less common triggers include exposure to airborne allergens (such as horse dander), human seminal fluid, cold water, or cold air.

Sometimes, a specific trigger cannot be identified, even after a thorough evaluation. This condition is called idiopathic anaphylaxis. (See "Patient education: Anaphylaxis treatment and prevention of recurrences (Beyond the Basics)".)

IgE-mediated anaphylaxis — In most people, anaphylaxis is caused by the presence of antibodies called immunoglobulin E (IgE). IgE antibodies are normally produced in the body for the purpose of fighting certain infections. In people with allergies, however, IgE is made in response to noninfectious substances, such as foods, medications, or insect venoms. This IgE then sticks to the outside of mast cells in body tissues and basophils, a type of white blood cell.

If a person with IgE antibodies to a specific allergen is exposed to that allergen again, these cells may suddenly become activated to release large amounts of inflammation-causing chemicals (including histamine and tryptase) into the bloodstream.

These chemicals cause the signs and symptoms typical of anaphylaxis (see 'Anaphylaxis symptoms' above). The allergic reaction can be so strong that it becomes life-threatening. For example, sudden severe swelling in the throat can lead to suffocation.

In some people with anaphylaxis, the reaction is caused by a process that does not involve allergens and IgE. Some people have too many mast cells or overly active mast cells. However, the symptoms and treatment are the same.


Some people are more likely than others to experience anaphylaxis or to develop severe symptoms during anaphylaxis. For example, those who have one or more of the following:

Previous severe anaphylactic reactions – People who have had allergic reactions to a particular substance in the past are at increased risk of anaphylaxis. However, the severity of past allergic reactions does not reliably predict the severity of future reactions. People with mild reactions in the past may experience severe anaphylactic reactions in the future.

Asthma and other chronic lung diseases – People with asthma or other chronic lung disease are more likely to have more severe respiratory problems during anaphylaxis.

Other diseases – People with cardiovascular disease, for example, and coronary artery disease, are also at greater risk of severe anaphylaxis.


The diagnosis of anaphylaxis is based on symptoms that occur within minutes to a few hours after exposure to a potential trigger, such as a food, medication, or insect sting.

Is it anaphylaxis or another problem? — Other health problems can cause symptoms that are similar to those of anaphylaxis. These include a severe asthma attack, a heart attack, a panic attack, or even food poisoning. After the acute anaphylactic episode, follow-up evaluation by an allergy specialist can help to clarify the diagnosis.

Tryptase is one of the natural chemicals released into the blood during an anaphylactic reaction. An increased amount of tryptase can sometimes be measured in a blood sample collected during the first three hours after anaphylaxis symptoms have begun (eg, after a medication has been taken or after an insect sting). However, tryptase levels are seldom elevated in food-induced anaphylaxis. A normal tryptase level does not exclude the diagnosis of anaphylaxis.


The treatment and prevention of anaphylaxis are discussed separately. (See "Patient education: Anaphylaxis treatment and prevention of recurrences (Beyond the Basics)".)


Your health care provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our website (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for health care professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: Anaphylaxis (The Basics)
Patient education: Food allergy (The Basics)
Patient education: Insect allergy (The Basics)
Patient education: Insect bites and stings (The Basics)
Patient education: Epinephrine autoinjectors (The Basics)
Patient education: Shortness of breath (dyspnea) (The Basics)
Patient education: Angioedema (The Basics)
Patient education: Peanut allergy (The Basics)
Patient education: Drug allergy (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Anaphylaxis treatment and prevention of recurrences (Beyond the Basics)
Patient education: Use of an epinephrine autoinjector (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Anaphylaxis: Emergency treatment
Bee, yellow jacket, wasp, and other Hymenoptera stings: Reaction types and acute management
Clinical manifestations of food allergy: An overview
Diagnosis of Hymenoptera venom allergy
Diagnostic evaluation of food allergy
Differential diagnosis of anaphylaxis in children and adults
Drug eruptions
Fatal anaphylaxis
Food-induced anaphylaxis
History and physical examination in the patient with possible food allergy
Immediate hypersensitivity reactions to radiocontrast media: Clinical manifestations, diagnosis, and treatment
Laboratory tests to support the clinical diagnosis of anaphylaxis
Pathophysiology of anaphylaxis

The following organizations also provide reliable health information.

American Academy of Allergy, Asthma & Immunology (www.aaaai.org/conditions-and-treatments/allergies/anaphylaxis)

American College of Allergy, Asthma & Immunology (acaai.org/)

Food Allergy Research & Education (www.foodallergy.org/)

Food Allergy Canada (foodallergycanada.ca/)

Anaphylaxis Campaign (www.anaphylaxis.org.uk/)


Literature review current through: Nov 2017. | This topic last updated: Mon Oct 09 00:00:00 GMT 2017.
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