Anaphylaxis
Anaphylactic reaction; Anaphylactic shock; Shock - anaphylactic; Allergic reaction - anaphylaxis
Anaphylaxis is a life-threatening type of
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.
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.
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.
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.
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.
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.
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.
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.
Causes
Anaphylaxis is a severe, whole-body allergic reaction to a chemical that has become an allergen. An allergen is a substance that 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 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 drugs (morphine, x-ray dye, aspirin, and others) may cause an anaphylactic-like reaction (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:
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
- Hives, itchiness, redness of the skin
- Nasal congestion
- Nausea or vomiting
- Palpitations
- 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 the person take or inject it. Do not give medicine through the mouth if the person is having difficulty breathing.
- 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.
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)
- Respiratory arrest (no breathing)
- Shock
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.
- If you have a history of serious allergic reactions, carry emergency medicines (such as a chewable antihistamine and injectable epinephrine or a bee sting kit) according to your provider's instructions.
- Do not use your injectable epinephrine on anyone else. They may have a condition (such as a heart problem) that could be worsened by this drug.
References
Barksdale AN, Muelleman RL. Allergy, hypersensitivity, and anaphylaxis. In: Walls RM, Hockberger RS, Gausche-Hill M, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, PA: Elsevier; 2018:chap 109.
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. Systemic anaphylaxis, food allergy, and insect sting allergy. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 238.
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
Version Info
Last reviewed on: 1/23/2022
Reviewed by: Stuart I. Henochowicz, MD, FACP, Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School, Washington, DC. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
