Anaphylaxis

Anaphylactic reaction; Anaphylactic shock; Shock - anaphylactic; Allergic reaction - anaphylaxis

Anaphylaxis is a life-threatening type of allergic reaction.

Causes

Anaphylaxis is a severe, whole-body allergic reaction to a chemical that has become an allergen. An allergen is a substance that, for most people, is harmless, but in some people, it can cause an allergic reaction.

After being exposed to a substance such as bee sting venom, the person's immune system becomes sensitized to it. When the person is exposed to that allergen again, an allergic reaction may occur. Anaphylaxis usually happens quickly after the exposure. The condition is severe and involves the whole body.

Tissues in different parts of the body release histamine and other substances. This causes the airways to tighten and leads to other symptoms.

Some medicines (morphine, x-ray dye, aspirin, and others) may cause an anaphylactic-like reaction (often called an anaphylactoid reaction) when people are first exposed to them. These reactions are not the same as the immune system response that occurs with true anaphylaxis. But, the symptoms, risk of complications, and treatment are the same for both types of reactions.

Anaphylaxis can occur in response to any allergen. Common causes include:

Medicine allergies
Medicine allergies
Drug allergies are a group of symptoms caused by an allergic reaction to a drug (medicine).
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Food allergies
Food allergies
A food allergy is a type of immune response triggered by eggs, peanuts, milk, shellfish or some other specific food.
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Insect bites/stings
Insect bites/stings
Insect bites and stings can cause an immediate skin reaction. The bite from fire ants and the sting from bees, wasps, and hornets are most often pai...
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Pollen and other inhaled allergens rarely cause anaphylaxis. Some people have an anaphylactic reaction with no known cause.

Anaphylaxis is life threatening and can occur at any time. Risks include a history of any type of allergic reaction.

Symptoms

Symptoms develop quickly, often within seconds or minutes. They may include any of the following:

Abdominal pain
Feeling anxious
Chest discomfort or tightness
Diarrhea
Difficulty breathing, coughing, wheezing, or high-pitched breathing sounds
Difficulty swallowing
Dizziness or lightheadedness
Dizziness
Dizziness is a term that is often used to describe 2 different symptoms: lightheadedness and vertigo. Lightheadedness is a feeling that you might fai...
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Lightheadedness
Fainting is a brief loss of consciousness due to a drop in blood flow to the brain. The episode most often lasts less than a couple of minutes and y...

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Hives, itchiness, redness of the skin
Hives
Hives are raised, often itchy, red bumps (welts) on the surface of the skin. They can be an allergic reaction to food or medicine. They can also ap...
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Nasal congestion
Nausea or vomiting
Palpitations
Palpitations
Palpitations are feelings or sensations that your heart is pounding or racing. They can be felt in your chest, throat, or neck. You may:Have an unpl...
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Slurred speech
Swelling of the face, eyes, or tongue
Unconsciousness

Exams and Tests

The health care provider will examine the person and ask about what might have caused the condition.

Tests for the allergen that caused anaphylaxis (if the cause is not obvious) may be done after treatment.

Treatment

Anaphylaxis is an emergency condition that needs medical attention right away. Call 911 or the local emergency number immediately.

Check the person's airway, breathing, and circulation, which are known as the ABC's of Basic Life Support. A warning sign of dangerous throat swelling is a very hoarse or whispered voice, or coarse sounds when the person is breathing in air. If necessary, begin rescue breathing and CPR.

Call 911 or the local emergency number.
Calm and reassure the person.
If the allergic reaction is from a bee sting, scrape the stinger off the skin with something firm (such as a fingernail or plastic credit card). Do not use tweezers. Squeezing the stinger will release more venom.
If the person has emergency allergy medicine on hand, help them take or inject it. Do not give medicine by the mouth if the person is having difficulty breathing. An epinephrine injector should be used immediately if it is available.
Take steps to prevent shock. Have the person lie flat, raise the person's feet about 12 inches (30 centimeters), and cover the person with a coat or blanket. Do not place the person in this position if a head, neck, back, or leg injury is suspected, or if it causes discomfort.
Shock
Shock is a life-threatening condition that occurs when the body is not getting enough blood flow. Lack of blood flow means the cells and organs do n...
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DO NOT:

Do not assume that any allergy shots the person has already received will provide complete protection.
Do not place a pillow under the person's head if they are having trouble breathing. This can block the airways.
Do not give the person anything by mouth if they are having trouble breathing.

Paramedics or other providers may place a tube through the nose or mouth into the airways. Or emergency surgery will be done to place a tube directly into the trachea.

The person may receive medicines to further reduce symptoms.

Outlook (Prognosis)

Anaphylaxis can be life threatening without prompt treatment. Symptoms usually do get better with the right therapy, so it is important to act right away.

Possible Complications

Without prompt treatment, anaphylaxis may result in:

Blocked airway
Cardiac arrest (no effective heartbeat)
Cardiac arrest
Cardiac arrest occurs when the heart suddenly stops beating. When this happens, blood flow to the brain and the rest of the body also stops. Cardia...

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Respiratory arrest (no breathing)
Respiratory arrest
Breathing that stops from any cause is called apnea. Slowed breathing is called bradypnea. Labored or difficult breathing is known as dyspnea....

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Shock
Death

When to Contact a Medical Professional

Call 911 or the local emergency number if you or someone you know develops severe symptoms of anaphylaxis. Or, go to the nearest emergency room.

Prevention

To prevent allergic reactions and anaphylaxis:

Avoid triggers such as foods and medicines that have caused an allergic reaction in the past. Ask detailed questions about ingredients when you are eating away from home. Also carefully examine ingredient labels.
If you have a child who is allergic to certain foods, introduce one new food at a time in small amounts so you can recognize an allergic reaction.
People who know that they have had serious allergic reactions should wear a medical ID tag or bracelet.
If you have a history of serious allergic reactions, carry injectable epinephrine according to your provider's instructions.
There is no contraindication to using epinephrine in a severe allergic reaction.

Open References

References

Barksdale AN, Ross W. Allergy, anaphylaxis, and angioedema. In: Walls RM, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 106.

Dreskin SC, Stitt JM. Anaphylaxis. In: Burks AW, Holgate ST, O'Hehir RE, et al, eds. Middleton's Allergy: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 75.

Schwartz LB, Castells M. Anaphylaxis. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 233.

Shaker MS, Wallace DV, Golden DBK, et al. Anaphylaxis-a 2020 practice parameter update, systematic review, and Grading of Recommendations, Assessment, Development and Evaluation (GRADE) analysis. J Allergy Clin Immunol. 2020;145(4):1082-1123. PMID: 32001253 pubmed.ncbi.nlm.nih.gov/32001253/.

Shock - illustration
Shock is a severe condition that occurs when not enough blood flows through the body, causing very low blood pressure, a lack of urine, and cell and tissue damage.
Shock
illustration
Allergic reactions - illustration
Allergic reaction can be provoked by skin contact with poison plants, chemicals and animal scratches, as well as by insect stings. Ingesting or inhaling substances like pollen, animal dander, molds and mildew, dust, nuts and shellfish, may also cause allergic reaction. Medications such as penicillin and other antibiotics are also to be taken with care, to assure an allergic reflex is not triggered.
Allergic reactions
illustration
Anaphylaxis - illustration
Anaphylaxis is an acute systemic (whole body) type of allergic reaction which occurs when a person has become sensitized to a certain substance or allergen and is again exposed to the allergen. Some drugs, such as those used for pain relief or for x-rays, may cause an anaphylactoid reaction on first exposure. Histamines and other substances released into the bloodstream cause blood vessels to dilate and tissues to swell. Anaphylaxis may be life threatening if obstruction of the airway occurs, if blood pressure drops, or if heart arrhythmias occur.
Anaphylaxis
illustration
Hives - illustration
Hives are raised red welts of various size on the surface of the skin, often itchy, which come and go. Also called uticaria, hives is usually part of an allergic reaction to drugs or food. The term dermatitis describes an inflammatory response of the skin, caused by contact with allergens or irritants, exposure to sunlight, or by poor circulation, even stress. AVOID SCRATCHING. Scratching the rash may spread the inflammation, lead to infection and even leave scars.
Hives
illustration
Food allergies - illustration
The body's immune system normally reacts to the presence of toxins, bacteria or viruses by producing a chemical reaction to fight these invaders. However, sometimes the immune system reacts to ordinarily benign substances such as food or pollen, to which it has become sensitive. This overreaction can cause symptoms from the mild (hives) to the severe (anaphylactic shock) upon subsequent exposure to the substance. An actual food allergy, as opposed to simple intolerance due to the lack of digesting enzymes, is indicated by the production of antibodies to the food allergen, and by the release of histamines and other chemicals into the blood.
Food allergies
illustration
Insect stings and allergy - illustration
Allergic reaction to bee stings occurs when a person becomes sensitized to the venom from a previous sting. This reaction is different from the reaction to the poison in the bite of a black widow spider, which injects a potent toxin into the blood. Ordinarily, bee venom is not toxic and will only cause local pain and swelling. The allergic reaction comes when the immune system is oversensitized to the venom and produces antibodies to it. Histamines and other substances are released into the bloodstream, causing blood vessels to dilate and tissues to swell. Severe reactions can lead to anaphylactic shock, a life-threatening series of symptoms including swelling of the throat and difficulty breathing. Persons who develop an allergy to bee stings should carry prescription bee sting kits to counteract the reaction to bee venom.
Insect stings and allergy
illustration
Allergic reactions to medication - illustration
A true allergy to a medication is different than a simple adverse reaction to the drug. The allergic reaction occurs when the immune system, having been exposed to the drug before, creates antibodies to it. On subsequent exposure to the drug these antibodies cause release of histamines. If severe, this reaction can result in a life-threatening situation known as anaphylactic shock.
Allergic reactions to medication
illustration
Antibodies - illustration
Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy substances containing antigens.
Antibodies
illustration

Shock - illustration
Shock is a severe condition that occurs when not enough blood flows through the body, causing very low blood pressure, a lack of urine, and cell and tissue damage.
Shock
illustration
Allergic reactions - illustration
Allergic reaction can be provoked by skin contact with poison plants, chemicals and animal scratches, as well as by insect stings. Ingesting or inhaling substances like pollen, animal dander, molds and mildew, dust, nuts and shellfish, may also cause allergic reaction. Medications such as penicillin and other antibiotics are also to be taken with care, to assure an allergic reflex is not triggered.
Allergic reactions
illustration
Anaphylaxis - illustration
Anaphylaxis is an acute systemic (whole body) type of allergic reaction which occurs when a person has become sensitized to a certain substance or allergen and is again exposed to the allergen. Some drugs, such as those used for pain relief or for x-rays, may cause an anaphylactoid reaction on first exposure. Histamines and other substances released into the bloodstream cause blood vessels to dilate and tissues to swell. Anaphylaxis may be life threatening if obstruction of the airway occurs, if blood pressure drops, or if heart arrhythmias occur.
Anaphylaxis
illustration
Hives - illustration
Hives are raised red welts of various size on the surface of the skin, often itchy, which come and go. Also called uticaria, hives is usually part of an allergic reaction to drugs or food. The term dermatitis describes an inflammatory response of the skin, caused by contact with allergens or irritants, exposure to sunlight, or by poor circulation, even stress. AVOID SCRATCHING. Scratching the rash may spread the inflammation, lead to infection and even leave scars.
Hives
illustration
Food allergies - illustration
The body's immune system normally reacts to the presence of toxins, bacteria or viruses by producing a chemical reaction to fight these invaders. However, sometimes the immune system reacts to ordinarily benign substances such as food or pollen, to which it has become sensitive. This overreaction can cause symptoms from the mild (hives) to the severe (anaphylactic shock) upon subsequent exposure to the substance. An actual food allergy, as opposed to simple intolerance due to the lack of digesting enzymes, is indicated by the production of antibodies to the food allergen, and by the release of histamines and other chemicals into the blood.
Food allergies
illustration
Insect stings and allergy - illustration
Allergic reaction to bee stings occurs when a person becomes sensitized to the venom from a previous sting. This reaction is different from the reaction to the poison in the bite of a black widow spider, which injects a potent toxin into the blood. Ordinarily, bee venom is not toxic and will only cause local pain and swelling. The allergic reaction comes when the immune system is oversensitized to the venom and produces antibodies to it. Histamines and other substances are released into the bloodstream, causing blood vessels to dilate and tissues to swell. Severe reactions can lead to anaphylactic shock, a life-threatening series of symptoms including swelling of the throat and difficulty breathing. Persons who develop an allergy to bee stings should carry prescription bee sting kits to counteract the reaction to bee venom.
Insect stings and allergy
illustration
Allergic reactions to medication - illustration
A true allergy to a medication is different than a simple adverse reaction to the drug. The allergic reaction occurs when the immune system, having been exposed to the drug before, creates antibodies to it. On subsequent exposure to the drug these antibodies cause release of histamines. If severe, this reaction can result in a life-threatening situation known as anaphylactic shock.
Allergic reactions to medication
illustration
Antibodies - illustration
Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy substances containing antigens.
Antibodies
illustration

Review Date: 3/31/2024

Reviewed By: Deborah Pedersen, MD, MS, Allergy & Asthma Care, PC, Taunton, MA. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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Health Library

Anaphylaxis

Allergic reaction

Causes

Allergen

Medicine allergies

Food allergies

Insect bites/stings

Symptoms

Dizziness

Lightheadedness

Hives

Palpitations

Exams and Tests

Treatment

CPR

Shock

Place a tube through the nose or mouth

Place a tube directly into the trachea

Outlook (Prognosis)

Possible Complications

Cardiac arrest

Respiratory arrest

When to Contact a Medical Professional

Prevention

References

Shock - illustration

Shock

Allergic reactions - illustration

Allergic reactions

Anaphylaxis - illustration

Anaphylaxis

Hives - illustration

Hives

Food allergies - illustration

Food allergies

Insect stings and allergy - illustration

Insect stings and allergy

Allergic reactions to medication - illustration

Allergic reactions to medication

Antibodies - illustration

Antibodies

Shock - illustration

Shock

Allergic reactions - illustration

Allergic reactions

Anaphylaxis - illustration

Anaphylaxis

Hives - illustration

Hives

Food allergies - illustration

Food allergies

Insect stings and allergy - illustration

Insect stings and allergy

Allergic reactions to medication - illustration

Allergic reactions to medication

Antibodies - illustration

Antibodies

Related Information