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  2. Conditions
  3. Anaphylaxis


  1. What is anaphylaxis?
  2. Symptoms
  3. Causes
  4. Diagnosis
  5. Treatment
  6. Prevention
  7. FAQs

What is anaphylaxis?

Anaphylaxis, also known as anaphylactic shock or an anaphylactic reaction, is an extreme allergic reaction affecting multiple organ systems of the body. Anaphylaxis is a medical emergency and requires immediate medical treatment.

It is characterized by rapidly-developing, life-threatening airway and/or breathing and/or blood circulation problems, usually within minutes of exposure to a trigger substance, but sometimes after hours.

The overall frequency of anaphylaxis remains unclear, because some clinicians use the term anaphylaxis only for the full-blown syndrome, whereas others use it to describe cases with milder symptoms. Some figures have put the overall prevalence of anaphylaxis as 1-2 percent of the population as a whole.[1]

Triggers for anaphylaxis are different from person to person, but are often everyday things such as insect stings, rubber, certain medications such as penicillin, or foods such as nuts, fish, shellfish, dairy products and eggs.

The symptoms tend to worsen quickly and may include an itchy red rash anywhere on the body, coughing or wheezing, difficulty breathing, nausea, alterations in heart rate, a sense of impending doom and, eventually, collapse and loss of consciousness.

For people at high risk, it may be useful to carry around an emergency kit with an adrenaline injection, especially when traveling to areas where medical help is not readily available. If treated quickly and appropriately, most people recover well after an episode of anaphylaxis.

Anaphylactic reactions tend to be more common in children and teenagers, though adults can also have reactions when they are exposed to triggers. The onset of an anaphylactic allergy can occur at any age.


The symptoms of anaphylaxis can come on, progress and become life-threatening very quickly.

The most common early symptoms of anaphylaxis include:[2][3]

  • Itchy skin, sometimes developing into hives, a rash of raised, pink or red areas known as wheals
  • Wheezing, hoarseness and chest tightness
  • Swelling of the lips, tongue and throat, known as angioedema
  • Swelling of eyes, hands and feet
  • Reddening of the skin
  • Irritation and inflammation of the eyes and nasal passages

As anaphylactic shock progresses, other symptoms may include:[2][4]

  • A sense of impending doom
  • A fast or thumping heart
  • Stomach cramps, nausea and vomiting

Advanced symptoms of anaphylaxis include:[2][4]

  • A high-pitched wheezing sound, known as stridor
  • Fast, shallow breathing or complete inability to breathe
  • Bluish skin on the lips and tongue
  • Confusion, agitation and anxiety
  • A sudden feeling of weakness or dizziness
  • Loss of consciousness

Types of anaphylactic reaction

Anaphylactic reactions may be divided into two main types:[2]

  • Uniphasic reactions have symptoms that get rapidly worse, but once treated, the symptoms go and then do not return.
  • Biphasic reactions may be mild or severe to start with and then appear to disappear before symptoms increase, with breathing and blood pressure problems.


Anaphylaxis is an extreme allergic response. Allergies occur when the immune system overreacts to a substance that it wrongly perceives as a threat. These substances are called allergens or triggers. Some people are sensitive to one or more allergens.

Good to know: Even a minute amount of an allergen can trigger an allergic reaction.[5]

In the case of anaphylaxis, the body’s allergic reaction goes into overdrive. The cells of the body release chemical substances which cause swelling in different areas.

This sets off a series of events which cause the body to lose control of its vital functions, the respiratory and/or cardiovascular system. The blood vessels widen, which leads to a drop in blood pressure. The tissues in the airways swell, which causes difficulty breathing and may completely block the airways. If air cannot be taken into the lungs, the blood cannot be oxygenated. Oxygenated blood is needed so that the cells of organs, such as the brain, can work. The heart muscle needs oxygen so that it can pump blood around the body. Once one major organ system starts to falter, the others become strained, potentially leading to failure of multiple organs and mortality.[4]


The trigger for anaphylactic shock reactions vary from person to person. Some of the most common triggers include:[6][7]

  • Certain foods, including nuts, shellfish, eggs, some fruits
  • Insect stings, particularly wasp stings and bee stings
  • Natural latex, also known as rubber, such as is found in condoms
  • Certain medications, including some antibiotics such as penicillin and non-steroidal anti-inflammatory drugs (NSAIDs), e.g. aspirin
  • General anaesthetic
  • Contrast agents: special dyes used in some medical tests

Many cases of anaphylaxis have no known cause. This is called idiopathic anaphylaxis.

Risk factors

There aren’t many known risk factors for anaphylaxis, but some factors that may increase risk include:[8]

  • Previous anaphylaxis
  • Allergies or asthma
  • Certain other conditions, including mastocytosis, an abnormal accumulation of mast cells, which release histamine and other substances during allergic reactions


The diagnosis is based on the recognition of symptoms occurring quickly and rapidly worsening. Treatment is not delayed in order to carry out further diagnostic tests, since an anaphylactic reaction is an emergency, and anyone with presumed anaphylaxis is treated as such.

After life-saving emergency treatment has been started and symptoms have been brought under control, a blood test can be done to identify anaphylaxis or rule out other causes of the symptoms. The blood test should be done as soon as possible and no later than four hours from the onset of symptoms. It measures mast cell tryptase, a chemical released by the immune system in a severe allergic reaction.[4][9]


Anaphylaxis is a life-threatening emergency and needs immediate treatment. Out of hospital, an ambulance must be called at once and the patient transported to an emergency department.[4]

First aid measures

While waiting for medical attention, first aid measures should be implemented immediately, including:[4][10]


Adrenaline should be injected immediately, where possible. Many people who are susceptible to anaphylaxis will carry an adrenaline auto-injector, also known as an adrenaline pen or epinephrine. This is a pre-filled syringe with a needle, that can be injected by the person having the anaphylactic reaction or by a bystander who knows how to use it.

If there is no response to the initial injection, it is recommended to give a further adrenaline dose after five minutes. Adrenaline is effective very soon after being administered and wears off quite quickly.

Patient positioning

A person in anaphylactic shock should be placed in a comfortable position. Depending on the symptoms experienced, different positions will be advised:

  • A person who feels faint, due to low blood pressure, should lie flat with their legs raised. Sitting or standing may cause cardiac arrest, a sudden loss of blood flow resulting from the failure of the heart to pump effectively
  • A person with airway and breathing problems may prefer to sit up, as this makes breathing easier
  • An unconscious person who is still breathing should be placed on their side in the recovery position[11]
  • A pregnant person should lie on their left side to avoid caval compression,i.e. compression of a large vein that leads to low blood pressure

Removing the trigger

Removing the trigger for anaphylaxis is not always possible, but may involve, for example:

Removing the stinger from a bee sting. Early removal is more important than removal method.

Rinsing mouth to remove traces of a food allergen. Attempts to make a person vomit after food-induced anaphylaxis are not recommended.

Cardiopulmonary resuscitation (CPR)

If the person is unresponsive and not breathing, CPR should be performed until the emergency services arrive. CPR is unlikely to make a person’s heart start beating again if it has stopped. However, it will pump some blood around the body, supplying organs and, most importantly, the brain with oxygen.

Good to know: If untrained, a person can still use hands-only CPR.

Hospital treatment

People with presumed anaphylaxis are treated in the emergency department. The specifics of treatment depend on how well or unwell the person experiencing an anaphylactic reaction is.

Treatment may include:[4][12]

  • Adrenaline, also known as epinephrine, usually injected into the thigh muscle.
  • Intravenous fluids to raise the blood pressure
  • Oxygen and inhalant medications
  • Steroids and antihistamines

In severe cases, a breathing tube may be necessary until the immune reaction settles.

Prevention and management

If a person has had one anaphylactic reaction, they are very likely to have another if exposed to the same allergen again. Subsequent episodes of anaphylaxis are often worse than the first one.

There are several ways to manage the possibility of having another anaphylactic reaction:[13]

Avoiding known triggers

It is important to take steps to avoid exposure to triggers. A person who has experienced anaphylaxis will be referred to a specialist allergy clinic to identify allergy triggers and for assessment and advice about how to avoid them in the future.

Some people who have had an anaphylactic episode in response to common substances or medication choose to wear a piece of jewelry, often a bracelet which has their allergy engraved on it, to direct medical staff in the case of emergencies.[4]

Being prepared for future emergencies

An epinephrine autoinjector should be carried at all times. They contain a prescribed single dose of anaphylaxis medication that is injected into the thigh during an anaphylactic emergency. A doctor will explain to the person affected how to use this. It is also important that other people in close contact, such as family members, also know how to use the autoinjector.

People at high risk of severe reactions should also have an anaphylaxis action plan for their school or workplace, which includes education on the prevention of exposure and how to act in cases of anaphylaxis.

Emergency anaphylaxis kits can also be prescribed in some cases. It is recommended that this include:[14]

An adrenaline injection, also known as an epinephrine pen, which is the most important. This works rapidly to reverse all signs of anaphylaxis, most importantly low blood pressure, poor heart rate, poor circulation, swelling and asthma.

H1 Antihistamine, which is particularly effective for skin symptoms and swelling, as a supporting medication to epinephrine.

H2 Antihistamine, which is particularly effective when there are cardiovascular symptoms, as a supporting medication. This will also reduce abdominal discomfort.

Allergen immunotherapy

For some people, it is possible to undergo allergen immunotherapy, also known as desensitization or hyposensitization therapy, which means the body is slowly exposed to the trigger responsible for their anaphylaxis. This causes the immune system to get used to the trigger gradually, helping to reduce the severity of the allergic reaction in the future.[15]


Q: Anaphylaxis vs anaphylactoid reaction – what is the difference?
A: Anaphylaxis is a life-threatening condition triggered by a wide range of allergens and involving multiple organ systems. It occurs after exposure to a foreign protein, known as an antigen, that stimulates the production of Immunoglobulin E (IgE) antibodies. These travel to cells and, after subsequent exposure to the antigen, stimulate the release of the chemicals that cause an allergic reaction.

Anaphylactoid reactions appear to be exactly the same as anaphylactic reactions, but they do not involve previous exposure to the antigen. Anaphylactoid reactions are most commonly seen in reactions to contrast media used to increase the contrast of structures or fluids within the body for medical imaging.[16]

Q: Allergic reaction vs anaphylaxis – what is the difference?
A: An allergy is an immune response to something that the body mistakenly perceives as a threat, such as pollen or animal dander. In most cases, people with allergies develop mild to moderate symptoms, which develop locally in the skin or eyes, for example.

Sometimes, exposure to a triggering allergen can cause anaphylaxis. This happens when a person’s immune system over-releases chemicals, so that the reaction involves the respiratory and/or cardiovascular system, which can be life threatening.

  1. NICE. "Anaphylaxis." Accessed 4 July 2018.

  2. Anaphylaxis Campaign. "Signs and Symptoms." Accessed 3 July 2018.

  3. AMBOSS. "Hypersensitivity reactions." Accessed 3 July 2018.

  4. Patient.info. "Anaphylaxis | Symptoms and Treatment." 14 February 2018. Accessed 3 July 2018.

  5. MedlinePlus Medical Encyclopedia. "Allergic reactions." 14 March 2016. Accessed 4 July 2018.

  6. NHS inform. "Anaphylaxis - Illnesses & conditions." 1 May 2018. Accessed 4 July 2018.

  7. Allergy UK. "Anaphylaxis and Severe Allergic Reaction." Accessed 4 July 2018.

  8. Wiley Online Library. "Causes and risk factors for anaphylaxis." 15 May 2011. Accessed 4 July 2018.

  9. Medscape eMedicine. "Anaphylaxis." 16 May 2018. Accessed 4 July 2018.

  10. Resuscitation Council. "Emergency treatment of anaphylactic reactions." Accessed 4 July 2018.

  11. The recovery position involves six steps, to help ensure a person’s airway is kept clear and open and that any vomit or fluid won’t cause them to choke. For information on how to move someone into the recovery position, see this resource with instructions.

  12. BNF - NICE. "Antihistamines, allergen immunotherapy and allergic emergencies." Accessed 4 July 2018.

  13. AAAAI "Anaphylaxis Symptoms, Diagnosis, Treatment & Management." Accessed 4 July 2018.

  14. Food Allergy & Anaphylaxis Connection Team. "Emergency Kit Contents.” Accessed 4 July 2018.

  15. Medscape eMedicine. "Anaphylaxis Treatment & Management." 16 May. 2018. Accessed 4 July 2018.

  16. BJA Education | Oxford Academic - Oxford Journals. "Anaphylaxis." 1 August 2004. Accessed 4 Jul. 2018.