What Is Anaphylaxis?

Anaphylaxis is an extreme form of allergic reaction that can be life-threatening. It may happen within a few seconds or minutes after being exposed to a substance that triggers an allergic response, such as peanuts or bee stings.

Anaphylaxis prompts the immune system to release a surge of chemicals that can lead to shock. This sudden release of chemicals can cause a sudden drop in blood pressure and constriction of airways, leading to breathing difficulties. Symptoms of anaphylaxis may include a rapid and feeble pulse, skin rash, nausea, and vomiting. Common triggers for this severe allergic reaction include certain foods, medications, insect venom, and latex.

To treat anaphylaxis, a shot of epinephrine is essential, and immediate medical attention is necessary. If epinephrine is not available, it is critical to seek urgent medical care. Delay in treatment of anaphylaxis can lead to a lethal outcome. Therefore, prompt medical attention is crucial.


Anaphylaxis (pronounced anna-fill-axis) is a severe and sudden allergic response that can occur when someone with allergies comes into contact with an allergen. Symptoms can begin within minutes (usually within the first hour of exposure) and progress rapidly but may also appear up to 2-3 hours later.1 Anaphylaxis is a potentially life-threatening condition that requires immediate emergency treatment. Even if you have not previously experienced anaphylaxis, if you have had a sudden allergic reaction in the past, you may be at risk.1 It is recommended that you see your GP and ask for a referral to an allergy clinic if you are concerned. While receiving a diagnosis of anaphylaxis can be overwhelming, educating oneself, planning, and using daily coping techniques can help individuals affected by this condition return to a normal life.1

Causes of anaphylaxis

The immune system generates antibodies to protect against foreign substances, which is beneficial when dealing with harmful bacteria or viruses. However, some individuals' immune systems may overreact to substances that typically do not cause allergic reactions.

Even if a person or their child has experienced a mild anaphylactic reaction previously, there is a risk of more severe anaphylaxis upon subsequent exposure to the allergen.3

For children, the most frequent anaphylaxis triggers are food allergies. Common food allergens include peanuts, tree nuts, fish, shellfish, wheat, soy, sesame, and milk.4

In adults, common triggers include:

  • Foods: nuts (peanuts, walnuts, cashews, almonds, hazelnut), milk, fish and shellfish, eggs, sesame, gluten, and some types of fruits: strawberries, bananas, kiwi5
  • Certain medications, such as antibiotics, aspirin, over-the-counter pain relievers, and intravenous (IV) contrast used in some imaging tests1,6
  • Stings from bees, yellow jackets, wasps, hornets, and fire ants1
  • Latex1

Anaphylaxis can also occur in some individuals from aerobic activities, like jogging, or even less strenuous activities, such as walking.7 Consuming specific foods prior to exercise or exercising in extreme weather conditions, has also been associated with anaphylaxis in some cases.8,9 Consult your healthcare provider for guidance on exercising safely.

If the cause of an allergy attack is unknown, tests can help identify the allergen. In some instances, the cause of anaphylaxis remains unidentified (idiopathic anaphylaxis).

Signs and symptoms of anaphylaxis

Anaphylaxis typically arises abruptly and intensifies rapidly. Its signs and symptoms involve:9

Other symptoms, such as an itchy raised rash (hives), nausea or vomiting, swelling (angioedema) of the tongue and lips, and abdominal pain, may also be present.

If you suspect that someone is having symptoms of anaphylaxis, it is important to administer an adrenaline injector according to the packaging instructions if one is accessible. Following this, immediately call your national emergency services number (999 in the UK). In case an adrenaline injector is not available, contact emergency services straight away. If you notice a potential trigger such as a bee or wasp sting embedded in their skin, cautiously remove it.

Management and treatment for anaphylaxis

You should know how to react when somebody is experiencing anaphylaxis. Anaphylaxis is a medical emergency and requires prompt treatment to avoid serious consequences. If someone displays symptoms of anaphylaxis, take the following steps:10 

  1. Dial 999 immediately for an ambulance and inform the emergency services that the individual may be experiencing anaphylaxis
  2. Have the person lie down and elevate their legs, unless they are having difficulty breathing, in which case they should sit up to assist their breathing. If the individual is pregnant, have them lie on their left side
  3. If an adrenaline auto-injector is available, use it immediately, but ensure you know how to administer it correctly beforehand
  4. If possible, remove any triggering substance, such as a stinger, carefully from the skin
  5. If symptoms persist after five minutes and another auto-injector is available, administer a second injection. If you are experiencing an anaphylactic reaction, you may follow these steps independently if you feel capable

In the event of an anaphylactic attack, you may require cardiopulmonary resuscitation (CPR) if you stop breathing or your heartbeat stops. Additionally, you may be given medications such as:10

  • Intramuscular epinephrine (adrenaline) to increase blood and oxygen flow to the body’s tissues
  • Oxygen to aid breathing
  • Intravenous (IV) antihistamines and cortisone to decrease inflammation of the airways and enhance breathing
  • A beta-agonist (such as salbutamol/ albuterol) to alleviate respiratory symptoms


To assist in making a diagnosis, your healthcare provider may inquire about previous allergic reactions, including reactions to specific foods, medicines, latex, and insect stings. Additionally, the following diagnostic procedures may be performed:10

  • A blood test to measure the level of a specific enzyme (tryptase), which can be elevated for up to three hours following anaphylaxis
  • Skin tests or blood tests to detect allergies that may assist in identifying the trigger

Because other conditions can share symptoms with anaphylaxis, your healthcare provider may want to exclude other possibilities as well.

Risk factors

Anaphylaxis has few established risk factors, but it is thought that certain factors may raise the likelihood of experiencing this severe allergic reaction. Previous episodes of anaphylaxis increase the risk of future reactions, which may also be more severe than the initial reaction. Individuals with allergies or asthma also have a higher risk of anaphylaxis.10 Additionally, certain medical conditions, such as heart disease and mastocytosis, can increase the risk of experiencing anaphylaxis.10


An anaphylactic reaction has the potential to be fatal as it can obstruct your breathing or stop your heart’s function. In the event of oxygen deprivation around the body, shock can occur, and blood pressure can drop severely. If left untreated, anaphylaxis has life-threatening complications. 


How can I prevent anaphylaxis?

If you have a severe allergy or have previously experienced anaphylaxis, it is crucial to take steps to prevent future occurrences. The following measures can help minimise your risk:

  •  Identify potential triggers by consulting an allergy clinic for allergy testing
  • Whenever possible, avoid potential triggers, such as taking care when food shopping or eating out if you have a food allergy
  • Always carry two up-to-date adrenaline auto-injectors with you and use one if you suspect you may be experiencing anaphylaxis
  • If possible, attend a local allergy or first-aid workshop to receive information on how to correctly use adrenaline auto-injectors

How common is anaphylaxis?

According to estimates by the World Allergy Organisation, the prevalence of allergies ranges from 10-40% in the general population across different countries.11,12 In the UK, the prevalence rates of allergic conditions are among the highest in the world, with more than 20% of the population experiencing one or more allergic disorders. Over the 20-year period leading up to 2012, there was a 615% increase in hospital admission rates for anaphylaxis in the UK.13

When should I see a doctor?

If you, your child, or someone you are with experiences a severe allergic reaction, seek emergency medical assistance immediately or dial 999. Do not wait to see if the symptoms subside. If you have an epinephrine auto-injector, administer it immediately during an attack.

However, even if the symptoms improve after the injection, it is still necessary to visit an emergency room to ensure that the symptoms do not recur, even without further exposure to the allergen. This second reaction is known as biphasic anaphylaxis.1

If you or your child has experienced a severe allergy attack or symptoms of anaphylaxis previously, schedule an appointment with your healthcare provider. Anaphylaxis diagnosis and long-term management can be complex, so it is likely that you will need to see an allergy and immunology specialist.


Anaphylaxis is a severe and life-threatening allergic reaction triggered by exposure to an allergen. Symptoms can range from mild to severe and require immediate medical attention, including the administration of epinephrine. People who are at risk of anaphylaxis should always carry an epinephrine auto-injector with them and receive appropriate education on how to use it. Timely recognition and treatment are crucial for good outcomes. 


  1. McLendon K, Sternard BT. Anaphylaxis. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023. Available from: http://www.ncbi.nlm.nih.gov/books/NBK482124/
  2. Justiz Vaillant AA, Vashisht R, Zito PM. Immediate hypersensitivity reactions. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jul 10]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK513315/
  3. Reber LL, Hernandez JD, Galli SJ. The pathophysiology of anaphylaxis. J Allergy Clin Immunol [Internet]. 2017 Aug [cited 2023 Jul 10];140(2):335–48. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5657389/
  4. Lee S. IgE-mediated food allergies in children: prevalence, triggers, and management. Korean J Pediatr [Internet]. 2017 Apr [cited 2023 Jul 10];60(4):99–105. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5410620/
  5. Gupta RS, Warren CM, Smith BM, Jiang J, Blumenstock JA, Davis MM, et al. Prevalence and severity of food allergies among us adults. JAMA Netw Open. 2019 Jan 4;2(1):e185630. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6324316/
  6. Montañez MI, Mayorga C, Bogas G, Barrionuevo E, Fernandez-Santamaria R, Martin-Serrano A, et al. Epidemiology, mechanisms, and diagnosis of drug-induced anaphylaxis. Front Immunol. 2017 May 29;8:614. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5446992/
  7. Povesi Dascola C, Caffarelli C. Exercise-induced anaphylaxis: A clinical view. Ital J Pediatr [Internet]. 2012 Sep 14 [cited 2023 Jul 10];38:43. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3483190/
  8. Minty B. Food-dependent exercise-induced anaphylaxis. Can Fam Physician. 2017 Jan;63(1):42–3. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5257219/
  9. Tupper J, Visser S. Anaphylaxis: A review and update. Can Fam Physician. 2010 Oct;56(10):1009-11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2954079/
  10. Cardona, V., Ansotegui, I. J., Ebisawa, M., El-Gamal, Y., Fernandez Rivas, M., Fineman, S., Geller, M., Gonzalez-Estrada, A., Greenberger, P. A., Sanchez Borges, M., Senna, G., Sheikh, A., Tanno, L. K., Thong, B. Y., Turner, P. J., & Worm, M. (2020). World allergy organization Anaphylaxis Guidance 2020. World Allergy Organization Journal, 13(10), 100472. https://doi.org/10.1016/j.waojou.2020.100472
  11. Baseggio Conrado, A., Ierodiakonou, D., Gowland, M. H., Boyle, R. J., & Turner, P. J. (2021). Food anaphylaxis in the United Kingdom: Analysis of national data, 1998-2018. BMJ. https://doi.org/10.1136/bmj.n251
  12. Pawankar, R. (2014). Allergic diseases and asthma: A global public health concern and a call to action. World Allergy Organization Journal, 7, 12. https://doi.org/10.1186/1939-4551-7-12
  13. Turner, P. J., Gowland, M. H., Sharma, V., Ierodiakonou, D., Harper, N., Garcez, T., Pumphrey, R., & Boyle, R. J. (2015). Increase in anaphylaxis-related hospitalizations but no increase in fatalities: An analysis of united kingdom national anaphylaxis data, 1992-2012. Journal of Allergy and Clinical Immunology, 135(4). https://doi.org/10.1016/j.jaci.2014.10.02
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Karina Silova

MSc Molecular Medicine and BSc Biomedicine, University of East Anglia, UK

My background is in key areas of biomedical research focusing on diseases and their molecular pathways to understand their root cause. I specialise in epigenetics and reproductive health; I am passionate about understanding diseases and helping to bridge the gap between medical science and the general public with accurate and understandable content while educating the public about health and diseases.

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