Anaphylaxis

Overview

Anaphylaxis is a severe, rapidly developing allergic reaction that affects the whole body and can be life-threatening. It happens when the immune system overreacts to a trigger, releasing chemicals that cause widespread effects within minutes to a couple of hours. These can include swelling of the airway, difficulty breathing, hives, and a sudden, dangerous drop in blood pressure.

Anaphylaxis is a medical emergency. The mainstay of treatment is an injection of epinephrine (adrenaline) given as soon as possible, followed by emergency medical care. People with known severe allergies are often prescribed an epinephrine auto-injector to carry at all times. Recognizing the warning signs and acting quickly can be life-saving, since the reaction can worsen rapidly.

Common Causes

Anaphylaxis is triggered when the immune system reacts strongly to an allergen. Common triggers include:

• Foods: peanuts, tree nuts, shellfish, fish, milk, eggs, and others. See food allergy.
• Insect stings: from bees, wasps, hornets, or fire ants.
• Medications: such as certain antibiotics and other drugs.
• Latex: in gloves and some medical products.
• Other triggers: rarely, exercise or no identifiable cause.

Anaphylaxis is closely related to other severe allergic responses such as angioedema and severe hives, and can lead to anaphylactic shock.

Associated Symptoms

Anaphylaxis typically affects more than one part of the body and comes on fast. Warning signs include:

• Difficulty breathing, wheezing, or throat tightness
• Swelling of the lips, tongue, throat, or face (facial swelling)
• Hives, widespread itching, or flushing
• Dizziness, fainting, or a sudden drop in blood pressure
• Rapid pulse, pale skin, or a sense of impending doom
• Nausea, vomiting, cramps, or diarrhea

Any combination of these after exposure to a known or possible allergen should be treated as anaphylaxis until proven otherwise.

Diagnosis & Evaluation

Anaphylaxis is diagnosed clinically from the sudden, multi-system reaction, and treatment must not wait for tests. Evaluation includes:

• Recognizing the pattern: rapid onset of breathing, skin, circulation, or gut symptoms after a likely trigger.
• History: known allergies, recent exposures, and previous reactions.
• Vital signs: blood pressure, pulse, breathing, and oxygen levels.
• Allergy testing later: skin or blood tests after recovery to identify the trigger.
• Specialist referral: to an allergist for an action plan and prevention.

Treatment & Management

Anaphylaxis is treated immediately. The key steps are:

• Epinephrine first: inject epinephrine into the outer thigh at the first signs, using an auto-injector if available. Do not delay.
• Call emergency services: always call for emergency help, even if symptoms improve.
• Position: lie the person down with legs raised, unless they are struggling to breathe or vomiting, in which case keep them comfortable.
• Second dose: a repeat epinephrine dose may be needed after 5 to 15 minutes if symptoms persist.
• Hospital care: oxygen, fluids, and monitoring, because symptoms can return hours later.
• Prevention: avoiding known triggers and carrying an epinephrine auto-injector at all times.

Self-Care & Prevention

Preventing anaphylaxis centers on avoiding triggers and being ready to act:

• Once a trigger is known, avoid it carefully, reading food labels and asking about ingredients when eating out.
• Carry your prescribed epinephrine auto-injector at all times and check its expiry date.
• Make sure family, friends, caregivers, and schools know your allergy and how to use the auto-injector.
• Wear a medical alert bracelet or carry a card describing your allergy.
• Keep an up-to-date emergency action plan from your allergist.
• Tell healthcare providers about drug allergies before any treatment or procedure.

If you are at risk of insect-sting anaphylaxis, take precautions outdoors. Acting at the very first signs with epinephrine, then calling emergency services, gives the best outcome.

When to See a Doctor

Anaphylaxis is always a medical emergency. Call emergency services immediately and use epinephrine right away if someone has signs such as:

• Difficulty breathing, wheezing, or throat tightness
• Swelling of the lips, tongue, throat, or face
• Widespread hives with dizziness, fainting, or pale skin
• A rapid, weak pulse or collapse after exposure to an allergen

Always seek emergency care even if symptoms ease after epinephrine, because the reaction can return. After any episode, see an allergist to confirm the trigger and get an emergency action plan.

Related Topics

Frequently Asked Questions

References

1. American Academy of Allergy, Asthma & Immunology (AAAAI). Anaphylaxis.
2. Mayo Clinic. Anaphylaxis — Symptoms and causes.
3. National Institute of Allergy and Infectious Diseases (NIAID). Food Allergy.
4. MedlinePlus, U.S. National Library of Medicine. Anaphylaxis.