What Is Anaphylaxis?

Woman going through anaphylaxis is injecting herself with an epi-pen in the thigh


Anaphylaxis is a severe and potentially life-threatening allergic reaction that occurs rapidly after exposure to an allergen (an allergy trigger). The reaction occurs due to an overreactive immune response to the allergen, which the body mistakenly perceives as harmful. These can be foods, medications, insect stings, latex, or something else.

During anaphylaxis, the immune system releases a flood of chemicals that can cause a range of body-wide symptoms, including difficulty breathing, swelling of the face and throat, rapid heartbeat, low blood pressure, gastrointestinal distress, and skin reactions like hives or itching.

Anaphylaxis is a medical emergency requiring immediate epinephrine (adrenaline) treatment to counteract the allergic reaction and stabilize symptoms. Some people may require additional treatments. When left untreated, anaphylaxis can progress rapidly, leading to complications or death.

About 1 in 50 Americans have experienced anaphylaxis. Understanding anaphylaxis is crucial for people at risk and their families—prompt recognition of the signs and symptoms and appropriate management can save lives.  

Anaphylaxis Symptoms 

Anaphylaxis symptoms develop suddenly and quickly progress. While specific symptoms can vary from person to person, anaphylaxis can affect the entire body.

Respiratory Symptoms

Breathing-related anaphylaxis symptoms can include:

Skin Symptoms

Anaphylaxis can affect the skin and may cause:

  • Hives (raised red bumps on the skin)
  • Itchiness 
  • Flushed appearance and a warm sensation throughout the body

Gastrointestinal Symptoms

Anaphylaxis symptoms that affect the digestive system can include:

  • Abdominal pain
  • Nausea
  • Diarrhea
  • Vomiting 

Cardiovascular Symptoms 

Anaphylaxis symptoms related to the heart can include:

  • Rapid heartbeat (tachycardia) 
  • Low blood pressure (hypotension)
  • Dizziness or fainting (syncope) 

Other Symptoms

Anaphylaxis symptoms may also include:

  • Swelling in the face, lips, tongue, or throat
  • Slurred speech
  • Anxiety or an impending sense of doom 


Anaphylaxis occurs when the immune system overreacts after exposure to an allergen. When some people with allergies come into contact with a trigger, their immune system sees it as a threat and releases a flood of chemicals, including histamine, which leads to the characteristic symptoms of anaphylaxis.

Allergens known to cause anaphylaxis include:

  • Certain foods, such as tree nuts, shellfish, peanuts, milk, and eggs
  • Medications, such as penicillin and nonsteroidal anti-inflammatory drugs (NSAIDs)
  • Insect stings and bites
  • Latex
  • High-intensity exercise, especially when paired with temperature or seasonal changes or after eating certain foods 

Risk Factors

Not everyone with allergies will go into anaphylaxis when exposed to an allergen. Several risk factors can increase the likelihood of experiencing anaphylaxis, including having:

  • Severe or life-threatening allergies
  • A personal history of asthma (especially if not well-controlled, which puts you at a higher risk of having a severe reaction)
  • Past anaphylactic reaction(s)
  • Heart disease


Anaphylaxis is primarily a clinical diagnosis, which means that healthcare providers rely on evaluating symptoms and medical history to make a diagnosis rather than relying solely on diagnostic tests.

Sometimes, healthcare providers may use diagnostic tests after treatment to confirm the diagnosis, determine what caused the anaphylactic response (if unknown), and help develop a comprehensive management plan to prevent future anaphylactic episodes. 

Diagnostic tests healthcare providers may use in the anaphylaxis diagnostic process include: 

  • Blood tests: A blood sample taken during or shortly after anaphylaxis allows healthcare providers to measure levels of an enzyme called tryptase, which is released by immune cells during an allergic reaction. 
  • Allergy testing: Skin prick allergy testing involves placing a small number of substances (allergens) on the skin, then scratching the skin to allow the substance to go under the skin’s surface. If you are allergic to the substance(s), your skin may become red, swollen, and itchy within minutes, indicating your immune system has produced allergen-specific IgE antibodies.

Phases of Anaphylaxis

There are two phases of anaphylactic reactions: the initial and the biphasic responses.

  • Initial anaphylactic reaction: This is the initial onset of symptoms after exposure to an allergen. These symptoms can range from mild to severe, typically occurring within minutes to an hour after exposure. The initial reaction occurs after the immune system releases chemicals (e.g., histamine) that cause widespread inflammation and affect various organ systems in the body. Immediate medical attention is essential during an initial anaphylactic reaction to prevent the progression of symptoms and potentially life-threatening complications.
  • Biphasic anaphylactic response: This is a less common occurrence characterized by symptoms returning after the initial reaction has been treated and resolved. This phase of the allergic response occurs hours after the initial reaction, even up to 72 hours later. During the biphasic phase, symptoms similar to those experienced in the initial reaction can reoccur. These symptoms are usually milder, though some may experience moderate to severe symptoms. 

Not everyone who has experienced anaphylaxis will have a subsequent biphasic response; about 16% of people who have had an anaphylactic reaction go on to have biphasic symptoms.

Treatments for Anaphylaxis  

Anaphylaxis is a medical emergency that requires prompt treatment to stop the allergic reaction and prevent life-threatening complications. 

Epinephrine (adrenaline) is the mainstay treatment for anaphylaxis. Epinephrine is administered via an auto-injector (e.g., EpiPen) as quickly as possible once anaphylaxis symptoms develop. Epinephrine works by constricting blood vessels and relaxing smooth muscles to counteract the immune response associated with anaphylaxis. It helps restore normal breathing, stabilize blood pressure, and relieve body-wide symptoms.

Seek medical attention if your symptoms don't resolve after using epinephrine. You may require further monitoring and need additional treatments, such as: 

  • Oxygen therapy: Supplemental oxygen can help deliver oxygen to vital organs if breathing difficulties persist. 
  • Antihistamines: Medications such as Zyrtec (cetirizine) or Allegra (fexofenadine) can help relieve itching, hives, and other allergic symptoms caused by histamine release.
  • Corticosteroids: Oral or intravenous corticosteroids, such as prednisone, help reduce inflammation.
  • Intravenous (IV) fluids: In cases of severe anaphylaxis, IV fluids can help regulate blood pressure and maintain hydration.


The best way to prevent anaphylaxis is to identify and avoid specific allergens, especially those that have caused previous anaphylactic reactions. This may involve carefully reading food labels, being cautious about cross-contamination, and taking necessary precautions to prevent insect stings, depending on your triggers. 

Other anaphylaxis prevention methods include:

  • Wear medical identification: Wear a medical bracelet or necklace that clearly states the specific allergens or triggers that can cause anaphylaxis. This helps alert others in case of an emergency.
  • Develop an anaphylaxis action plan: Work with a healthcare provider to create an individualized emergency action plan outlining the steps to take during anaphylaxis. This plan may include instructions on recognizing symptoms, administering epinephrine, and seeking immediate medical attention.
  • Carry an epinephrine auto-injector: If you have severe allergies, you must always carry an epinephrine auto-injector and know how to use it correctly.
  • Educate yourself and others: Learn about anaphylaxis, your triggers, and the signs of a reaction. Educate family members, friends, and caregivers on recognizing and responding to anaphylaxis.
  • Regular follow-up with a healthcare provider: Regularly visit a healthcare provider (e.g., an allergist) to update your emergency action plan and discuss any changes in triggers or allergy management strategies.


If anaphylaxis goes untreated or treatment is delayed, serious health complications can occur, including:

  • Shock: A sudden drop in blood pressure may prevent the body’s organs from receiving enough blood and oxygen to function properly and lead to permanent organ damage (e.g., kidney failure).
  • Cardiac arrest: Anaphylaxis can cause a rapid or irregular heartbeat, leading to a potential cardiac arrest in severe cases.
  • Respiratory failure: Anaphylaxis can cause swelling in the airways, making it difficult to breathe. In severe cases, respiratory failure can occur, which can be life-threatening.

Living With the Risk of Anaphylaxis

Living with severe allergies that put you at risk of anaphylaxis requires ongoing management and vigilance to prevent and address potential allergic reactions. Strict avoidance of known triggers is crucial to lowering your risk of anaphylactic reactions. Regular communication with healthcare providers, keeping your medications (e.g., EpiPen) up to date, and educating others about allergies and anaphylaxis are essential steps to help you feel prepared if you are exposed to a trigger.

Living with the threat of anaphylaxis can take an emotional toll on many people with severe allergies. You may find it helpful to seek support from healthcare providers, allergy support groups, or a therapist who can help provide valuable coping mechanisms and strategies to manage any anxiety or fear related to potential allergic reactions.

Frequently Asked Questions

  • What is the difference between anaphylactic shock and anaphylaxis?

    Anaphylaxis is a severe allergic reaction that can cause various symptoms, including difficulty breathing, rapid heart rate, and low blood pressure. Anaphylactic shock is a term used to describe when anaphylaxis causes a sudden drop in blood pressure, leading to inadequate blood flow to organs and tissues, potentially leading to organ failure. Anaphylactic shock is a severe manifestation of anaphylaxis.

  • How quickly does anaphylactic shock happen?

    Anaphylactic shock can occur rapidly, typically within minutes to hours after exposure to an allergen or trigger. The onset can vary depending on the individual and the specific circumstances, but it is generally characterized by a swift and potentially life-threatening drop in blood pressure.

  • What is the survival rate of anaphylaxis?

    Most people survive anaphylaxis when treatment (epinephrine) is administered promptly. In the United States, the fatality rate for anaphylaxis is about 0.3%.

  • Can anaphylaxis cause long-term damage?

    In some cases, anaphylaxis can cause long-term damage. Severe anaphylactic reactions that lead to prolonged oxygen deprivation or complications such as cardiac arrest or respiratory failure may result in permanent organ damage. When treated promptly, the risk of long-term damage is significantly reduced. 

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Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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