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{{short description|Life-threatening allergic reaction}}
{{lead too long|reason=material on the need for medical attention regardless of the use of emergency medication on site, and even if symptoms appear to be improving, appears twice in the lead|date=September 2024}}
{{cs1 config|name-list-style=vanc}}{{Infobox medical condition (new)
| name
| types
| image
| symptoms
▲| field = [[Allergy and immunology]]
▲| symptoms = Itchy rash, throat swelling, numbness, shortness of breath, lightheadedness, low blood pressure<ref name=NIH2015/>
▲| complications =
▲| onset = Over minutes to hours<ref name=NIH2015/>
▲| duration =
▲| causes = Insect bites, foods, medications<ref name=NIH2015/>
| diagnosis
▲| risks =
| differential
▲| diagnosis = Based on symptoms<ref name=IAP2003>{{cite book|last1=Caterino|first1=Jeffrey M.|last2=Kahan|first2=Scott|title=In a Page: Emergency medicine|date=2003|publisher=Lippincott Williams & Wilkins|isbn=9781405103572|page=132|url=https://books.google.com/books?id=O0LwFPZDKbsC&pg=PA132|language=en|url-status=live|archive-url=https://web.archive.org/web/20170908184018/https://books.google.ca/books?id=O0LwFPZDKbsC&pg=PA132|archive-date=2017-09-08}}</ref>
▲| differential = [[Allergic reaction]], [[angioedema]], [[asthma exacerbation]], [[carcinoid syndrome]]<ref name=IAP2003/>
▲| prevention =
▲| treatment = [[Epinephrine (medication)|Epinephrine]], [[intravenous fluids]]<ref name=NIH2015/>
▲| medication =
▲| frequency = 0.05–2%<ref name=World11/>
▲| deaths =
}}
<!--Definition and symptoms -->
'''Anaphylaxis''' (Greek: {{lang|grc-latn|ana-}} 'up' + {{lang|grc-latn|phylaxis}} 'guarding') is a serious, potentially fatal [[Allergy|allergic reaction]] and [[medical emergency]] that is rapid in onset and requires immediate medical attention regardless of the use of emergency medication on site.<ref name="Samp2006">{{cite journal |vauthors=Sampson HA, Muñoz-Furlong A, Campbell RL |title= Second symposium on the definition and management of anaphylaxis: summary report—Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium |journal= The Journal of Allergy and Clinical Immunology |volume= 117 |issue= 2 |pages= 391–7 |date= February 2006 |pmid= 16461139|doi= 10.1016/j.jaci.2005.12.1303|display-authors= etal|doi-access= free |url=https://www.jacionline.org/article/S0091-6749%2805%2902723-5/fulltext }}</ref><ref name=Tint10>{{cite book |author= Tintinalli, Judith E. |title= Emergency Medicine: A Comprehensive Study Guide (Emergency Medicine (Tintinalli))|publisher= McGraw-Hill Companies |location= New York |year= 2010 |pages= 177–182 |isbn= 978-0-07-148480-0 }}</ref> It typically causes more than one of the following: an itchy rash, throat closing due to swelling that can obstruct or stop breathing; severe tongue swelling that can also interfere with or stop breathing; [[shortness of breath]], [[vomiting]], lightheadedness, loss of consciousness, [[Hypotension|low blood pressure]], and [[Shock (circulatory)|medical shock]].<ref name="Overview - Anaphylaxis">{{cite web |author1=NHS |title=Overview – Anaphylaxis |url=https://www.nhs.uk/conditions/anaphylaxis/ |website=NHS (National Health Service) |publisher=British government |access-date=4 March 2022 |location=United Kingdom |language=English |date=29 November 2019}}</ref><ref name=NIH2015/> These symptoms typically start in minutes to hours and then increase very rapidly to life-threatening levels.<ref name=NIH2015/> Urgent medical treatment is required to prevent serious harm and death, even if the patient has used an [[epipen]] or has taken other medications in response, and even if symptoms appear to be improving.<ref name="Overview - Anaphylaxis"/>
<!-- Cause, mechanism, and diagnosis -->
Common causes include allergies to [[insect bite]]s and stings, [[Food allergy|allergies to foods]] – including nuts, milk, fish, shellfish, eggs and some fresh fruits or dried fruits; allergies to sulfites – a class of food preservatives and a byproduct in some fermented foods like vinegar; allergies to medications – including some antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin;<ref>{{Cite book |title=Oxford Handbook of Emergency Medicine |publisher=Oxford Medical Productions |edition=4th |page=42}}</ref> allergy to general anaesthetic (used to make people sleep during surgery); allergy to contrast agents – dyes used in some medical tests to help certain areas of the body show up better on scans; allergy to [[latex]] – a type of rubber found in some rubber gloves and condoms.<ref name="Overview - Anaphylaxis"/><ref name=NIH2015/> Other causes can include physical exercise, and cases may also occur in some people due to escalating reactions to simple throat irritation or may also occur without an obvious reason.<ref name="Overview - Anaphylaxis"/><ref name=NIH2015>{{cite web|title=Anaphylaxis|url=https://www.niaid.nih.gov/topics/anaphylaxis/Pages/default.aspx|publisher=National Institute of Allergy and Infectious Diseases|access-date=4 February 2016|date=April 23, 2015|archive-url=https://web.archive.org/web/20150504041904/http://www.niaid.nih.gov/topics/anaphylaxis/Pages/default.aspx|archive-date=4 May 2015}}</ref> The mechanism involves the release of inflammatory mediators in a rapidly escalating cascade from certain types of [[white blood cell]]s triggered by either [[Immune system|immunologic]] or non-immunologic mechanisms.<ref name=Khan11>{{cite journal|last=Khan|first=BQ|author2=Kemp, SF|title=Pathophysiology of anaphylaxis|journal=Current Opinion in Allergy and Clinical Immunology|date=August 2011|volume=11|issue=4|pages=319–25|pmid=21659865|doi=10.1097/ACI.0b013e3283481ab6|s2cid=6810542}}</ref> Diagnosis is based on the presenting symptoms and signs after exposure to a potential [[allergen]] or irritant and in some cases, reaction to physical exercise.<ref name="Overview - Anaphylaxis"/><ref name=NIH2015/>
<!--Prevention and management -->
The primary treatment of anaphylaxis is [[epinephrine (medication)|epinephrine]] [[intramuscular|injection into a muscle]], [[intravenous fluid]]s, then placing the person "in a reclining position with feet elevated to help restore normal blood flow".<ref name=NIH2015/><ref name=EAACI2014>{{cite journal|author=The EAACI Food Allergy and Anaphylaxis Guidelines Group|title=Anaphylaxis: guidelines from the European Academy of Allergy and Clinical Immunology.|journal=Allergy|date=August 2014|volume=69|issue=8|pages=1026–45|pmid=24909803|doi=10.1111/all.12437|s2cid=11054771}}</ref> Additional doses of epinephrine may be required.<ref name=NIH2015/> Other measures, such as [[antihistamine]]s and [[corticosteroids|steroids]], are complementary.<ref name=NIH2015/> Carrying an [[epinephrine autoinjector]], commonly called an "epipen", and identification regarding the condition is recommended in people with a history of anaphylaxis.<ref name=NIH2015/> Immediately contacting ambulance / EMT services is always strongly recommended, regardless of any on
<!--Epidemiology, prognosis, and history -->
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==Etymology==
▲<span title="Ancient Greek transliteration" class="Unicode" style="white-space:normal; text-decoration: none">[[Romanization of Greek|<small>romanized</small>]]: ''phylaxis''</span> <small>[[Literal translation|lit.]]</small> 'protection'.<ref>{{cite book|last1=Gylys|first1=Barbara|title=Medical Terminology Systems: A Body Systems Approach|date=2012|publisher=F.A. Davis|isbn=9780803639133|page=269|url=https://books.google.com/books?id=cR5hAQAAQBAJ&pg=PA269|url-status=live|archive-url=https://web.archive.org/web/20160205065649/https://books.google.ca/books?id=cR5hAQAAQBAJ&pg=PA269|archive-date=2016-02-05}}</ref>
==Signs and symptoms==
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===Other===
Gastrointestinal symptoms may include severe crampy [[abdominal pain]]
==Causes==
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===Venom===
[[Venom]] from stinging or biting insects such as [[Hymenoptera]] (ants, bees, and wasps) or [[Triatominae]] (kissing bugs) may cause anaphylaxis in susceptible people.<ref name=EAACI2014/><ref name="Klotz">{{cite journal|last=Klotz|first=JH|author2=Dorn, PL |author3=Logan, JL |author4=Stevens, L |author5=Pinnas, JL |author6=Schmidt, JO |author7=Klotz, SA |title="Kissing bugs": potential disease vectors and cause of anaphylaxis|journal=Clinical Infectious Diseases |date=Jun 15, 2010|volume=50|issue=12|pages=1629–34|pmid=20462351|doi=10.1086/652769|doi-access=free}}</ref><ref name=2001simonga>{{cite journal |first1=Simon G. A. |last1=Brown |first2=Qi-Xuan |last2=Wu |first3=G. Robert H. |last3=Kelsall |first4=Robert J. |last4=Heddle
===Risk factors===
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Anaphylaxis is a severe [[Allergy|allergic reaction]] of rapid onset affecting many [[Biological system|body systems]].<ref name=Tint10/><ref name=Khan11/> It is due to the release of [[Inflammation|inflammatory mediators]] and [[cytokine]]s from mast cells and [[Basophil granulocyte|basophils]], typically due to an [[Immune system|immunologic reaction]] but sometimes non-immunologic mechanism.<ref name=Khan11/>
[[Interleukin]] (IL)–4 and IL-13 are cytokines important in the initial generation of antibody and inflammatory cell responses to anaphylaxis.
===Immunologic===
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===Post-mortem findings===
In a person who died from anaphylaxis, [[autopsy]] may show an "empty heart" attributed to reduced venous return from [[vasodilation]] and redistribution of intravascular volume from the central to the peripheral compartment.<ref name="v005">{{
==Prevention==
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===Epinephrine===
[[File:Epipen.jpg|thumb|upright=1.3|An old version of an EpiPen brand auto-injector]]
[[Epinephrine (medication)|Epinephrine]] (adrenaline) (1 in 1,000) is the primary treatment for anaphylaxis with no absolute [[contraindication]] to its use.<ref name=EAACI2014/> It is recommended that an epinephrine solution be given [[Intramuscular injection|intramuscularly]] into the mid anterolateral thigh as soon as the diagnosis is suspected.<!-- <ref name=EAACI2014/> --> The injection may be repeated every 5 to 15 minutes if there is insufficient response.<ref name=EAACI2014/> A second dose is needed in 16–35% of episodes with more than two doses rarely required.<ref name=EAACI2014/> The intramuscular route is preferred over [[Subcutaneous tissue|subcutaneous]] administration because the latter may have delayed absorption.<ref name=EAACI2014/><ref name=Epi10>{{cite journal|last=Simons|first=KJ|author2=Simons, FE|title=Epinephrine and its use in anaphylaxis: current issues|journal=Current Opinion in Allergy and Clinical Immunology|date=August 2010|volume=10|issue=4|pages=354–61|pmid=20543673|doi=10.1097/ACI.0b013e32833bc670|s2cid=205435146}}</ref> It is recommended that after diagnosis and treatment of anaphylaxis, the patient should be kept under observation in an appropriate clinical setting until symptoms have fully resolved.<ref name="pmid32001253">{{cite journal | vauthors = Shaker MS, Wallace DV, Golden DK, Oppenheimer J, Bernstein JA, Campbell RL, Dinakar C, Ellis A, Greenhawt M, Khan DA, Lang DM, Lang ES, Lieberman JA, Portnoy J, Rank MA, Stukus DR, Wang J, Riblet N, Bobrownicki AP, Bontrager T, Dusin J, Foley J, Frederick B, Fregene E, Hellerstedt S, Hassan F, Hess K, Horner C, Huntington K, Kasireddy P, Keeler D, Kim B, Lieberman P, Lindhorst E, McEnany F, Milbank J, Murphy H, Pando O, Patel AK, Ratliff N, Rhodes R, Robertson K, Scott H, Snell A, Sullivan R, Trivedi V, Wickham A, Shaker MS, Wallace DV, Shaker MS, Wallace DV, Bernstein JA, Campbell RL, Dinakar C, Ellis A, Golden DK, Greenhawt M, Lieberman JA, Rank MA, Stukus DR, Wang J, Shaker MS, Wallace DV, Golden DK, Bernstein JA, Dinakar C, Ellis A, Greenhawt M, Horner C, Khan DA, Lieberman JA, Oppenheimer J, Rank MA, Shaker MS, Stukus DR, Wang J
People on [[Beta blocker|β-blockers]] may be resistant to the effects of epinephrine.<ref name=CEA11/> In this situation if epinephrine is not effective intravenous [[glucagon]] can be administered which has a mechanism of action independent of [[Adrenergic receptor|β-receptor]]s.<ref name=CEA11/>
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==Epidemiology==
The number of people who get anaphylaxis is 4–100 per 100,000 persons per year,<ref name=CEA11/><ref name=Tej2015>{{cite journal|last1=Tejedor-Alonso M|first1=A|last2=Moro-Moro|first2=M|last3=Múgica-García|first3=MV|title=Epidemiology of Anaphylaxis: Contributions From the Last 10 Years.|journal=Journal of Investigational Allergology & Clinical Immunology|date=2015|volume=25|issue=3|pages=163–75; quiz follow 174–5|pmid=26182682}}</ref> with a [[Cumulative incidence|lifetime risk]] of 0.05–2%.<ref>{{cite book|author1=Leslie C. Grammer|title=Patterson's Allergic Diseases|date=2012|publisher=Lippincott Williams & Wilkins |isbn=9781451148633|edition=7|url=https://books.google.com/books?id=MWdT7W4_N8sC&pg=PA199|url-status=live|archive-url=https://web.archive.org/web/20150620140057/https://books.google.ca/books?id=MWdT7W4_N8sC&pg=PA199|archive-date=2015-06-20}}</ref> About 30% of affected people get more than one attack.<ref name=Tej2015/> Exercise-induced anaphylaxis affects about 1 in 2000 young people.<ref name=Pravetton2016rev/>
Rates appear to be increasing: the numbers in the 1980s were approximately 20 per 100,000 per year, while in the 1990s it was 50 per 100,000 per year.<ref name=Review09/> The increase appears to be primarily for food-induced anaphylaxis.<ref>{{cite journal|last=Koplin|first=JJ|author2=Martin, PE |author3=Allen, KJ|title=An update on epidemiology of anaphylaxis in children and adults|journal=Current Opinion in Allergy and Clinical Immunology|date=October 2011|volume=11|issue=5|pages=492–6|pmid=21760501|doi=10.1097/ACI.0b013e32834a41a1|s2cid=13164564}}</ref> The risk is greatest in young people and females.<ref name=EAACI2014/><ref name=CEA11/>
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Richet and Portier extracted a toxin called hypnotoxin from their collection of jellyfish (but the real source was later identified as [[Portuguese man o' war]])<ref>{{cite journal |last=Suput |first=Dusan |title=Interactions of Cnidarian Toxins with the Immune System |url=https://www.eurekaselect.com/article/33767 |journal= Inflammation & Allergy - Drug Targets|year=2011 |language=en |volume=10 |issue=5 |pages=429–437 |doi=10.2174/187152811797200678|pmid=21824078 }}</ref> and sea anemone (''[[Actinia sulcata]]'').<ref name=":2">{{cite journal |last1=Boden |first1=Stephen R. |last2=Wesley Burks |first2=A. |date=2011 |title=Anaphylaxis: a history with emphasis on food allergy: Anaphylaxis: a history with emphasis on food allergy |journal=Immunological Reviews |language=en |volume=242 |issue=1 |pages=247–257 |doi=10.1111/j.1600-065X.2011.01028.x |pmc=3122150 |pmid=21682750}}</ref> In their first experiment on the ship, they injected a dog with the toxin in an attempt to immunise the dog, which instead developed a severe reaction ([[hypersensitivity]]). In 1902, they repeated the injections in their laboratory and found that dogs normally tolerated the toxin at first injection, but on re-exposure, three weeks later with the same dose, they always developed fatal shock. They also found that the effect was not related to the doses of toxin used, as even small amounts in secondary injections were lethal.<ref name=":2" /> Thus, instead of inducing tolerance ([[prophylaxis]]) which they expected, they discovered effects of the toxin as deadly.<ref>{{cite journal |last=May |first=Charles D. |date=1985 |title=The ancestry of allergy: Being an account of the original experimental induction of hypersensitivity recognizing the contribution of Paul Portier |journal=Journal of Allergy and Clinical Immunology |language=en |volume=75 |issue=4 |pages=485–495 |doi=10.1016/S0091-6749(85)80022-1|pmid=3884689 |doi-access=free }}</ref>
In 1902, Richet introduced the term ''aphylaxis'' to describe the condition of lack of protection. He later changed the term to ''anaphylaxis'' on grounds of [[euphony]].<ref name="His11">{{cite journal |last=Boden |first=SR |author2=Wesley Burks, A |title=Anaphylaxis: a history with emphasis on food allergy |journal=Immunological Reviews |date=July 2011 |volume=242 |issue=1 |pages=247–57 |pmid=21682750 |doi=10.1111/j.1600-065X.2011.01028.x |pmc=3122150}}, citing May CD, "The ancestry of allergy: being an account of the original experimental induction of hypersensitivity recognizing the contribution of Paul Portier", ''J Allergy Clin Immunol.'' 1985 Apr; 75(4):485–495.</ref> The term is from the [[Classical Greek|Greek]] {{lang|grc-Grek|ἀνά-|italic=no}},
==Research==
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