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Definition of Anaphylaxis

Anaphylaxis is an acute, life-threatening hypersensitivity reaction, involving the whole body, which is usually brought on by something eaten or injected.


The term anaphylaxis is often used only for a severe allergic reaction affecting the whole body. A second term, non-allergic anaphylaxis, may be used to describe identical reactions that are not caused by allergy, but involve other mechanisms in the body.

The clinical diagnosis and management are identical, whatever the cause of the anaphylaxis.

Symptoms of Anaphylaxis

Anaphylaxis is a medical emergency that develops rapidly and can be fatal. A few or all of the following symptoms, often developing in this order, may be experienced:

  • Itching of the lips, tongue and palate, swelling of the lips, tongue and throat
  • Swelling of the eyelids, itchy, watery eyes
  • Generalized itching, flushing, swelling of the skin, and hives (urticaria)
  • Increased heart rate
  • Abdominal cramps, nausea, vomiting, diarrhea
  • Difficulty in breathing due to throat swelling, wheezing and asthma
  • A sense of impending doom
  • Collapse, loss of consciousness, weakness and faintness caused by a drop in blood pressure.

Severe initial symptoms can develop within minutes following an encounter with an allergen, and usually reach peak severity within 3-30 minutes. Sometimes there can be a second phase reaction, 1–8 hours after the initial anaphylaxis.

Causes of Anaphylaxis

1. Anaphylaxis Caused by an Allergen

After a first encounter with an allergen, for example a bee sting, the allergic person can develop a particular type of antibody known as immunoglobulin E (IgE). This antibody is unique in that it attaches to cells in the body called mast cells and cells in the bloodstream known as basophils. The next time the individual is stung by a bee, the allergy antibodies attached to the cells react to the bee venom. This binding of the antibodies to cells and basophils with the bee venom allergen causes the release of chemicals, including histamine, into the bloodstream. The systemic allergic reaction that follows is called anaphylaxis. The whole body is involved. The reactions can be mild, and only involve the skin (hives or welts, redness of the skin and generalized itching), to severe (severe shortness of breath and/or unconsciousness with loss of blood pressure).


In theory, any food protein is capable of causing anaphylaxis. Foods most frequently responsible for anaphylaxis are:

  • Peanut (a legume)
  • Tree nuts (walnut, hazel nut/filbert, cashew, pistachio nut, Brazil nut, pine nut, almond)
  • Fish
  • Shellfish (shrimp, crab, lobster, oyster, scallops)
  • Milk (cow, goat)
  • Hen’s eggs
  • Seeds (cotton seed, sesame, psyllium, mustard)
  • Fruits, vegetables.

Rarely, food sensitivity can be so severe that anaphylaxis can occur after allergen inhalation, such as the odor of cooked fish or the opening of a package of peanuts.

A severe allergy to pollen, for example, ragweed, grass or tree pollen, can indicate that an individual may be susceptible to anaphylaxis or to the oral allergy syndrome (severe itching in the mouth and throat, with or without facial swelling) caused by eating certain plant-derived foods. This is due to the close relationship between proteins found in both the pollens and the foods.

Specific examples of these types of associations are:

  • Birch pollen: apples, raw potatoes, carrots, celery and hazelnuts
  • Mugwort pollen: celery, apple, peanut and kiwifruit
  • Ragweed pollen: melons (watermelon, cantaloupe, honeydew, etc) and bananas
  • Latex: bananas, avocado, kiwifruit, chestnut and papaya

Food-associated, exercise-induced anaphylaxis may occur when individuals exercise within 2-4 hours after ingesting a food they are allergic to. The combination of the exercise and the food can cause anaphylaxis, but the individual is able to exercise without symptoms or ingest the food without symptoms.

Antibiotics and Other Drugs
Penicillin, Cephalosporin and Muscle Relaxants Used in Anesthesia

Penicillin is the most common cause of anaphylaxis, for whatever reason, not just drug-induced cases.

Serious reactions to penicillin occur more frequently if the drug is injected or given intravenously, rather than taken by mouth.

Muscle relaxants, which are commonly used in anesthetic procedures, can cause an allergic reaction in some people.


The venom in the stings of bee, wasp, yellow-jacket, hornet and fire ant (Hymenoptera species) contain enzymes which are capable of causing anaphylaxis.


Latex is a milky sap produced by the rubber tree, Hevea brasiliensis. Anaphylaxis caused by latex can be a serious complication of medical procedures, such as internal examinations, dentistry or surgery. Medical and dental staff may develop occupational allergy through the use of especially powdered latex gloves. Latex has a wide variety of everyday uses, for example in balloons, rubber gloves, condoms, elastic, rubber bands, erasers and rubber toys.

Elective Medical Procedures

Allergen immunotherapy (hyposensitization) injections, which are given to treat allergies, can induce anaphylaxis, so the injections must be administered in a doctor’s office or a hospital where emergency equipment is available. The length of time a patient is asked to wait under medical supervision following an allergen immunotherapy injection varies among countries, but is usually from 20 minutes to an hour.

Foreign Proteins

Anaphylaxis can occur in response to a number of proteins that are foreign to the body, such as insulin or seminal fluid.

2. Non-allergic Anaphylaxis
Aspirin, Ibuprofen, Indomethacin

Allergy antibodies against aspirin and similar non-steroidal anti-inflammatory drugs have not been identified. The reactions can be very severe. People who are affected by these drugs can usually take choline or sodium salicylates, drugs which are very similar to aspirin, but differ slightly in their chemical composition.

Sulfiting Agents: Sodium and Potassium Sulfites, Bisulfites, Metabisulfites, Gaseous Sulfur Dioxides

These chemicals are added to foods and drinks to prevent deterioration and are also used as preservatives in a variety of medications. Sulfites are converted to gas in the stomach and are then inhaled. Rarely, they can cause asthma and anaphylaxis in susceptible people.

Whole Blood, Serum, Plasma, Serum Products, Immunoglobulins 

Anaphylactic reactions can occur after the administration of whole blood or its products. A mismatched blood transfusion can cause anaphylaxis.

Individuals who have a serum protein deficiency may become sensitized to the missing proteins when they are provided in blood products.

Radiocontrast Media, Low-molecular Weight Chemicals Used in

When injected into the body, these chemicals can cause the release of histamine and other inflammatory chemicals from cells in the body and blood stream, resulting in anaphylaxis.

Idiopathic Causes

Women may rarely suffer anaphylaxis attacks as a result of hypersensitivity caused by the progesterone secreted during the menstrual cycle.

Where recurrent symptoms of flushing, increased heart-rate, skin rashes, skin swelling, and difficulty breathing occur, but no recognized cause can be found, these cases are sometimes referred to as idiopathic (unknown cause) anaphylaxis.

Emergency Treatment of Anaphylaxis

Emergency medical assistance should be sought at the first sign of anaphylaxis. The sooner the attack is treated, the less severe it will be.

If the patient carries an epinephrine injection kit, this should be administered into a muscle immediately while the ambulance is awaited. If there is no improvement after several minutes, a second injection should be given. Even if the attack responds to the epinephrine injection, the patient should be transferred to the hospital for further observation, because of the risk that a second phase anaphylaxis attack may develop.

Treatment in the hospital may involve the use of glucocorticosteroid and antihistamine drugs in addition to adrenalin.

Prevention of Anaphylaxis

An individual who has suffered anaphylaxis should seek immediate medical help in identifying the cause of the reaction.

The patient’s family doctor should be informed as soon as possible about the attack. The doctor should be asked to provide a prescription for at least two epinephrine (adrenalin) auto-injector syringes and to train the patient and his/her family how to use them. Patients should carry a syringe at all times and have a spare at home. As soon as a syringe is used it must be replaced immediately.

It is important to ensure that each epinephrine syringe is within its "use-by" date; the effectiveness of the injection rapidly decreases after this date.

A referral to an allergy specialist for appropriate blood tests should be arranged, to help identify the allergy antibodies present in the blood, and to determine the allergen likely to have caused anaphylaxis. An allergist will be able to explain how to recognize the symptoms that occur at the onset of anaphylaxis.

Patients judged by a doctor to be at risk, and those who have experienced an anaphylaxis episode, should consider wearing a medical alert bracelet or necklet detailing known allergies.

At home, work and school, others should be alerted to the patient’s problem, and what to do in an emergency.

Advice for Avoiding Food Allergens
  • Ask your doctor for a referral to a dietician who can advise you about food labeling; there are many hidden ingredients in processed food. For example, peanuts in ice cream and cow’s milk protein in fast food – "Emulgator" is often the cow’s milk protein casein
  • Read food labels carefully
  • When eating at a restaurant or hotel, advise the chef and waiter of your allergy
  • If you are traveling abroad, obtain a translation card in the language of the country you are visiting, explaining what you are allergic to, and what should be done in the event of an emergency (Translation cards can be obtained from the British Allergy Foundation)
  • Contact your local allergy organization for support and advice about coping with anaphylaxis
  • Make sure that school teachers and school meal supervisors are informed about a child’s food allergies.
Advice for Preventing Insect Stings
  • Avoid potential contact with stinging insects: Stay clear of areas where stinging insects build or have nests, and be careful when picking ripe fruit or when such fruit is on the ground under a fruit tree
  • Keep food covered at all times, particularly outdoors. Keep barbecues and waste disposal areas clean
  • Don’t wear perfume, bright colors, and bold or flower-print clothing
  • Keep an insecticide spray in the car
  • Wear closed-toe shoes outdoors and don’t go barefoot
  • Don’t wear loose-fitting garments that can trap insects.

Allergen immunotherapy (hyposensitization/desensitization injections) are very effective in preventing further reactions to insect stings. As the allergist administers doses of venom in increasingly higher concentrations over time, the patient’s immune system becomes resistant to the effects of the venom.

Advice for Preventing Drug Reactions
  • Ensure that your doctor and dentist are informed immediately if a reaction occurs to a drug which has been prescribed
  • Any new physician who is consulted should be notified of drug reactions
  • Check the content of cold and flu treatments to make sure they do not contain a drug to which you react.
Advice for Avoiding Latex Reactions
  • Avoid contact with natural latex products
  • Inform physicians and other health care professionals, family, employers and school personnel about the allergy
  • Use synthetic products instead of natural latex products
  • Health care professionals should avoid the use of powdered latex gloves to prevent inhalation of latex proteins attached to the powder
  • Some foods contain the same allergenic proteins as latex and may need to be avoided. These are avocados, bananas, kiwi fruit and European chestnuts, as well as others
Other Conditions Which have Similar Symptoms to Anaphylaxis
  • anxiety attacks
  • severe asthma
  • swallowing or inhaling a foreign body
  • blood clots in the lungs (pulmonary embolism)
  • inflammation of the tissues at the top of the throat
  • heart attack
  • hormone-producing tumor in the small intestine (carcinoid syndrome)
  • hereditary angioedema
  • increased output of hormones from the adrenal gland (pheochromocytoma)
  • low blood sugar
  • seizures
  • overdoses of medications
  • hives brought on by exposure to cold temperature (cold urticaria)
  • hives brought on by emotion, temperature, etc (cholinergic urticaria)
  • sulfite or monosodium glutamate ingestion

If anaphylaxis occurs during a medical procedure it is important to consider a possible reaction to latex or anesthetic drugs.

Epidemiology: How Common Is Anaphylaxis, and Who Is Likely To Suffer?

Food-induced Anaphylaxis

The prevalence of food-induced anaphylaxis varies with the dietary habits of a region. In the USA, studies indicate that approximately 29,000 food-anaphylactic episodes occur each year. Food allergy has been reported to account for over one-half of all severe anaphylactic episodes in Italian children treated in emergency departments, and for one-third to one-half of anaphylaxis cases treated in emergency departments in North America, Europe and Australia. Anaphylaxis is thought to be less common in non-Westernized countries.

Risk factors for food anaphylaxis include asthma, pollen allergy and previous allergic reactions to the causative food.

Anaphylaxis Caused by Radiocontrast Media

Mild adverse reactions are experienced by approximately 5% of patients receiving radiocontrast media in radiological procedures. Figures from the USA suggest that severe systemic reactions occur in 1:1000 exposures, with a risk of death in 1:10,000-40,000 exposures.

Penicillin-induced Anaphylaxis

1% to 5% of courses of penicillin therapy are complicated by hypersensitivity reactions, and anaphylaxis accounts for 0.2% of treatments. Death occurs in 0.02% of treatments.

If an individual has a strong positive skin test, or IgE antibodies, to penicillin there is a 50-60% risk of anaphylaxis occurring if penicillin is given again. The risk of anaphylaxis caused by penicillin is low if tests are negative. Atopy - the ability of a person to develop IgE antibodies that cause allergy - is not a risk factor for the development of penicillin allergy and sensitivity to molds is not relevant. The risk of a person with a history suggestive of penicillin allergy reacting to cephalosporin antibiotics is less than 1%.

Insect Venom Anaphylaxis

Studies from France, Australia, the U.S.A. and Switzerland suggest incidences of anaphylaxis caused by Hymenoptera venom ranging from 0.4% to 4% of the population.

Food-associated, Exercise-induced Anaphylaxis

This is more common in females, and over 60% of cases occur in individuals less than 30 years of age.


Anaphylaxis is a severe hypersensitivity reaction that can be fatal.

It is essential to identify the cause of anaphylaxis in order to prevent further occurrence.

Individuals with a history of anaphylaxis should carry an epinephrine injector kit with them at all times.

If, while eating a particular food or after being stung by an insect, you start to notice symptoms that you suspect could develop into anaphylaxis, do not delay in seeking treatment; tell someone what is happening immediately, and get to the hospital as soon as possible. If an epinephrine injection is available, use it immediately.

Links to Additional Information on Anaphylaxis

Allergy Awareness Association New Zealand

Allergy Society of South Africa (ALLSA) Go to online literature, then to anaphylaxis.

American Academy of Allergy, Asthma and Immunology (AAAAI) que_es_la_anafilaxis.stm  (in Spanish)

Anaphylaxis Campaign (UK):

Australasian Society of Clinical Immunology and Allergy (ASCIA)

British Allergy Foundation Click on translation cards.

Food Allergy Network (USA)

Food Anaphylactic Children Training Support (Australia)

Mayo Clinic (USA)