What is anaphylaxis?

August 2022   Linda Armstrong  |  ✓  Medically reviewed by: Gary Falcetano, PA-C, AE-C; Fabio Iachetti, MD; Rebecca Rosenberger, MMSc, PA-C

A licensed Physician Assistant with more than 25 years of diverse experience in emergency and disaster medicine, primary care, and allergy and immunology, Gary Falcetano is the U.S. Clinical Affairs Manager for Allergy in ImmunoDiagnostics at Thermo Fisher Scientific. Fabio Iachetti is a licensed physician with more than 15 years of diverse experience in several disease areas such as allergy, CV, pain, GI, rheumatology, urology, and diabetology. He is a Senior Medical Manager for Allergy in ImmunoDiagnostics Global Medical Affairs at Thermo Fisher Scientific. In addition to being a practicing Physician Assistant in the field of allergy and immunology for more than 20 years, Rebecca Rosenberger is the Associate Director for Clinical Affairs & Education, ImmunoDiagnostics at Thermo Fisher Scientific.

Anaphylaxis is a severe and potentially life-threatening allergic reaction.1 Like other allergy symptoms, it’s triggered when the immune system overreacts and releases histamine (among other chemicals) in response to an allergen, such as peanuts, shellfish, latex, insect venom, dust mites, and countless more.2

Often, histamine causes symptoms such a runny nose, itchy/watery eyes, etc.3 But sometimes, the body releases a flood of chemicals that can send the body into anaphylactic shock.1 Blood pressure may drop suddenly, and airway tissues may swell, causing wheezing, shortness of breath, and loss of consciousness among other symptoms. If not treated immediately, anaphylaxis may lead to death.3

While anaphylaxis is rare, it’s an extremely serious condition, and dealing with it can be scary. But studying the causes, signs, and symptoms of anaphylaxis and learning about potential risk factors and management strategies may help lessen anxiety and prepare you and others to deal with anaphylaxis if it occurs. So here’s a primer to help you do just that.

What are the signs and symptoms of anaphylaxis?

Each anaphylactic experience is unique. However, there are several common symptoms, most of which occur within five to 30 minutes of contacting the allergen. However, in some cases, symptoms can start more than an hour later.3

While some people show life-threatening reactions almost immediately, others may experience early signs of anaphylaxis. Particularly for anyone with a history or high risk of anaphylaxis, it’s important to recognize early symptoms (if present) and immediately seek treatment.4

Initial Signs of Anaphylaxis

When exhibited, early signs of anaphylaxis may include:3-5

  • Itchy mouth, throat, eyes, and/or face
  • Patchy red skin, hives, welts
  • Itchy scalp, palms, and/or soles of feet, possibly extending to the ear canal, lips, and/or genitals
  • Nasal congestion
  • Throat tightness, hoarseness, and/or changes in the tone of voice
  • Swelling of lips and/or tongue

For some people, the first signs of anaphylaxis are far more severe and usually involve more than one part of the body, such as the skin, mouth, lungs, heart, and/or gut.6

Severe Anaphylaxis Symptoms

Along with the initial signs of anaphylaxis, additional symptoms may include:3,5,6

  • Shortness of breath, trouble breathing, coughing and/or wheezing (i.e., a whistling sound while breathing)
  • Dizziness and/or fainting
  • Stomach cramping, pain, bloating, vomiting, and/or diarrhea
  • Uterine cramps
  • Feelings of dread or impending doom
  • Chest tightness
  • Trouble swallowing
  • Increased heart rate and/or low blood pressure
  • Weak pulse
  • Confusion
  • Sudden weakness
  • Dizziness/fainting
  • Loss of consciousness

According to the Cleveland Clinic (a nonprofit academic medical center), approximately 20 percent of people with anaphylaxis experience biphasic anaphylaxis. With this type of reaction, people experience some of the aforementioned symptoms, which then go away. However, hours or sometimes even days after this first wave of symptoms, they experience a second round of severe symptoms.3

Given the risks of biphasic reactions, it’s important to monitor people who have experienced anaphylaxis for hours or perhaps even days after they’ve seemingly recovered.  

What causes anaphylaxis?

While there may be other causes of anaphylaxis, such as exerciseallergens are the main culprits. Among them, food allergens are the most frequent triggers of anaphylaxis in children, and insect venom and various drug allergies are the most prevalent offenders in adults.7 Additionally, according to an article published in The Journal of Allergy and Clinical Immunology, drugs are the most common reported cause of fatal anaphylaxis in countries such as Australia, New Zealand, the United Kingdom, Brazil, and the United States.8

Here are some of the most common allergies that can cause anaphylaxis, along with some links to help you learn more about each one. 

While a wide range of foods may cause anaphylaxis, the most commonly implicated foods for both adults and children worldwide are:

Other perhaps less-common causes of food-induced anaphylaxis may include:9-15

Natural rubber latex is found in items such as gloves, condoms, balloons, and more. Sometimes, latex causes only a mild skin irritation in sensitized individuals; other times it can trigger a severe allergic reaction. In fact, according to the Asthma and Allergy Foundation of America, inhaling small latex particles, perhaps from being in the vicinity of someone donning and/or removing latex gloves, may be enough to trigger a reaction.6

Anaphylaxis may also be caused by allergies to the following drugs and contrast agents:6,15-17

  • Penicillin and other antibiotics
  • Nonsteroidal anti-inflammatory drugs (NSAIDs), e.g., aspirin and aspirin-related products
  • Insulin
  • Muscle relaxants (e.g., suxamethonium, alcuronium, vecuronium, pancuronium, and atracurium, which are widely used in general anesthesia)
  • Biologics and monoclonal antibodies
  • Contrast agents (i.e., special dyes to help internal body parts or functions show up better on scans) 

Venom from stinging insects (such as bees, yellow jackets, wasps, and hornets) and bites from fire ants may cause anaphylaxis.6 Anaphylaxis caused by insect-venom allergy has been reported in 3 percent of adults and 1 percent of children who’ve been stung.16 Additionally 80 to 90 percent of fatal insect venom anaphylaxis occurs in men 50 to 60 years old on average.8

What are some anaphylaxis risk factors?

While anaphylaxis is somewhat unpredictable, several factors may increase the risk of anaphylaxis. 

  • Previous anaphylaxis. The risk of anaphylaxis is elevated for those that have already experienced it; plus, subsequent reactions may be more severe.1
  • Cardiovascular disease. According to one study, 71 percent of fatal drug anaphylaxis occurred in people with cardiovascular disease.8
  • Mastocytosis. While rare, mastocytosis is caused by an excess amount of mast cells in body tissues.18 While it leads to a host of symptoms depending on condition type, people with systemic mastocytosis have an increased risk of anaphylaxis.16
  • Asthma. Asthma affects 70 to 75 percent of those suffering fatal food anaphylaxis in the United Kingdom and Australia, according to a recent study.8
  • Exercise. Exercise-induced anaphylaxis typically occurs after vigorous physical activity.6 Symptoms may initially include fatigue, flushing, and skin conditions such as hives, welts, and/or a rash.16 Additional risk factors that may affect exercise-induced anaphylaxis include the use of drugs or alcohol, temperature and seasonal changes, and consumption of foods prior to exercise.6 The most common foods that may be related to this condition in adults include celery, shellfish, cheese, tomatoes, and alcohol.4
  • Other factors. Stress, acute infections, and perimenstrual status may also increase the risk for anaphylaxis.8

What can you do to prevent and treat anaphylaxis?

To reduce the risk of anaphylaxis, it’s critical for those with allergies to first understand which allergens they’re sensitized to and to then take steps to reduce exposure. One of the best ways to identify your possible triggers is a simple blood test.

Paired with your symptom history and physical exam, a specific IgE blood test for allergies can help your healthcare provider determine exactly which allergens may cause allergic reactions. Additionally, a specific IgE allergen component test (along with other factors) may help your provider better predict your risk of a serious reaction such as anaphylaxis.   

To prepare for a healthcare visit, complete our symptom tracker, which will generate a comprehensive symptom profile you can then review with your healthcare provider to decide if a specific IgE blood test is right for you.

Once you’ve identified your triggers, there are several steps you can take to prepare for and/or prevent a reaction and to deal with emergencies.

  • Wear a medical-alert ID, such as a necklace or bracelet.1  
  • Keep an emergency kit with any prescribed medications available at all times.1
  • Ensure any epinephrine autoinjectors (e.g., EpiPen, Jext, Emerade) are current (as opposed to expired).1
  • Provide personalized anaphylaxis information to anyone that interacts with children with severe allergies or a history of anaphylaxis. Ensure that everyone he or she regularly comes into contact with is aware of the risk and understands what to do an emergency situation. Consider informing people such as school nurses, teachers, daycare providers, coaches, neighbors, parents of the affected child’s friends, etc.19
  • Educate yourself about generic drugs and brand names for drugs that may cause reactions (if applicable). Be especially aware of ingredients in combination products and become familiar with drugs that could cause cross-reactions.6
  • Avoid food-allergen exposure (if applicable) via tactics such as:1,6
    • Reading food labels carefully to check for potential allergens,
    • Asking restaurants how each dish is prepared, what ingredients it contains, and what cross-contamination efforts are employed, and
    • Preventing cross contamination while cooking by washing hands, surfaces, utensils, etc.
  • Employ insect-venom-related precautions (if applicable), such as refraining from:1
    • Walking barefoot in the grass,
    • Wearing bright colors, perfumes, colognes, and scented lotions, which may attract insects, and
    • Drinking and/or eating from soda cans and containers that have been outdoors and may conceal insects. 
  • Ask your healthcare provider to create an anaphylaxis action plan to help you better prepare for an emergency.6
  • Educate your family, friends, and co-workers about your allergies (or those of your child) and how to recognize symptoms of anaphylaxis.3
  • Ensure all healthcare providers are aware of your allergies, especially if you plan to have a medical procedure.3
  • Learn more about exposure-reduction strategies specific to your unique allergic triggers via our more than 60 individual Allergen Fact Sheets.

If someone is showing signs of anaphylaxis—such as pale, cool, and clammy skin; a weak, rapid pulse; trouble breathing; confusion; and/or loss of consciousness—the Mayo Clinic suggests you immediately do the following:19

  • Call your local emergency phone number (e.g., 911 in the United States, 112 in Europe).
  • Make sure the person is lying down and elevate the legs.
  • Use an epinephrine autoinjector, if available.
  • Check the person's pulse and breathing, and if necessary administer CPR or other first-aid measures.

For more articles like this, check out our Living with Allergies section of our website and our Allergen Fact Sheets, which provide basic info and exposure-reduction tips for more than 60 allergens, including mold, pet dander, cockroaches, dust mites, pollen, alpha-Gal, insect venom, and more). 

Tools for Understanding Allergies


Track allergy symptoms and prepare for a visit with a healthcare provider.

Learn about specific allergens, including common symptoms, management, and relief. 

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  1. Mayo Clinic [Internet] Anaphylaxis. Rochester, MN: Mayo Foundation for Medical Education and Research; 2021 Oct. 2. Available from: https://www.mayoclinic.org/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468
  2. American Academy of Allergy, Asthma & Immunology [Internet] Allergic Reaction Defined. Milwaukee WI, American Academy of Allergy, Asthma & Immunology. Accessed July 2022. Available from:  https://www.aaaai.org/tools-for-the-public/allergy,-asthma-immunology-glossary/allergic-reaction-defined.
  3. Cleveland Clinic [Internet]. Cleveland OH: Cleveland Clinic; 2021 Jan 13. Available from: https://my.clevelandclinic.org/health/diseases/8619-anaphylaxis.
  4. Cianferoni A, Muraro A. Food-induced anaphylaxis. Immunol Allergy Clin North Am. 2012 Feb;32(1):165-95. doi: 10.1016/j.iac.2011.10.002. Epub 2011 Nov 21. PMID: 22244239; PMCID: PMC3440177. Available from: chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3440177/pdf/nihms339803.pdf
  5. American Academy of Allergy, Asthma & Immunology [Internet]. Milwaukee WI, American Academy of Allergy, Asthma & Immunology. Accessed July 2022. Available from: https://www.aaaai.org/conditions-treatments/allergies/anaphylaxis
  6. Asthma and Allergy Foundation of America [Internet]. Arlington, VA: Asthma and Allergy Foundation of America; 2017 Feb.  Available from: https://www.aafa.org/anaphylaxis-severe-allergic-reaction/
  7. Worm M, Babina M, Hompes S. Causes and risk factors for anaphylaxis. J Dtsch Dermatol Ges. 2013 Jan;11(1):44-50. doi: 10.1111/j.1610-0387.2012.08045.x. Epub 2012 Nov 26. PMID: 23181736. Available from: https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1610-0387.2012.08045.x.
  8. Turner PJ, Jerschow E, Umasunthar T, Lin R, Campbell DE, Boyle RJ. Fatal Anaphylaxis: Mortality Rate and Risk Factors. J Allergy Clin Immunol Pract. 2017 Sep-Oct;5(5):1169-1178. doi: 10.1016/j.jaip.2017.06.031. PMID: 28888247; PMCID: PMC5589409. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5589409/#:~:text=Up%20to%205%25%20of%20the,with%20hospital%20admissions%20for%20anaphylaxis.
  9. Mayo Clinic [Internet] Alpha gal. Rochester, MN: Mayo Foundation for Medical Education and Research; 2021 Oct. 2. Available from: https://www.mayoclinic.org/diseases-conditions/alpha-gal-syndrome/symptoms-causes/syc-20428608.
  10. The University of Manchester [Internet]. Manchester, UK: The University of Manchester; 2006 Oct 18. Available from: http://research.bmh.manchester.ac.uk/informall/allergenic-food/index.aspx?FoodId=12.
  11. Anaphylaxis UK [Internet] Fruit. Accessed July 2022. Available from: https://www.anaphylaxis.org.uk/fact-sheet/vvegetables-allergy/.
  12. Anaphylaxis UK [Internet] Vegetables. Accessed July 2022. Available from: https://www.anaphylaxis.org.uk/fact-sheet/fruit-allergy/.
  13. Food Allergy Canada [Internet]. Toronto, Canada. Accessed July 2022. Available from: https://foodallergycanada.ca/allergies/mustard.
  14. American College of Allergy, Asthma & Immunology [Internet] Arlington Heights, IL: American College of Allergy, Asthma & Immunology. Accessed July 2022. Available from: https://acaai.org/allergies/allergic-conditions/food.
  15. Lockey R. World Allergy Organization [Internet]. Milwaukee, WI: World allergy Organization; 2019 April. Available from: https://www.worldallergy.org/education-and-programs/education/allergic-disease-resource-center/professionals/anaphylaxis-synopsis.
  16. Irani, Anne-Marie, and Elias G Akl. “Management and Prevention of Anaphylaxis.” F1000Research vol. 4 F1000 Faculty Rev-1492. 22 Dec. 2015, doi:10.12688/f1000research.7181.1 Available from: chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4754021/pdf/f1000research-4-7737.pdf
  17. NHS [Internet]. United Kingdom. 2021 Nov 1. Available from: https://www.nhs.uk/conditions/anaphylaxis.
  18. NHS [Internet] Mastocytosis. United Kingdom. 2019 June 19. Available from: https://www.nhs.uk/conditions/anaphylaxis. Available from: https://www.nhs.uk/conditions/mastocytosis.
  19. Mayo Clinic [Internet] Anaphylaxis Diagnosis. Rochester, MN: Mayo Foundation for Medical Education and Research; 2021 Oct. 2. Available from: https://www.mayoclinic.org/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468