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Overview

What Is Anaphylaxis?

Anaphylaxis is a rapid, severe allergic reaction that can affect breathing, blood pressure, the skin, digestion, and other body systems. It can begin within minutes after exposure to a trigger, although symptoms may sometimes appear later. Anyone can experience anaphylaxis, including people with a known allergy and people having a first reaction. Because it can quickly become life-threatening, suspected anaphylaxis needs emergency treatment right away.

Emergency Warning Signs

Emergency Warning Signs of Anaphylaxis

Act now

Suspected anaphylaxis is an emergency

Use prescribed epinephrine immediately and call emergency services. Symptoms may occur together or progress quickly, so do not wait for every warning sign or for symptoms to become severe.

  • Trouble breathing
  • Swelling of the tongue
  • Tightness in the throat
  • Wheezing
  • Hives
  • Sudden dizziness
  • Fainting
  • Vomiting
  • Severe abdominal pain
  • A weak or rapid pulse

Symptoms

Symptoms of Anaphylaxis

  • Hives
  • Flushed or pale skin
  • Swelling of the lips
  • Swelling of the tongue
  • Throat tightness
  • Hoarse voice
  • Wheezing
  • Shortness of breath
  • Vomiting
  • Cramping abdominal pain
  • Confusion
  • Fainting

Anaphylaxis may start with symptoms that seem mild, but the reaction can worsen rapidly. A rash or hives does not have to be present, so breathing problems, faintness, or sudden symptoms affecting more than one body system should be taken seriously. Recognizing anaphylaxis symptoms early can help prompt immediate epinephrine and emergency care.

Causes

Causes and Triggers of Anaphylaxis

During anaphylaxis, the immune system can rapidly activate mast cells and basophils, which release inflammatory chemicals such as histamine. These chemicals can widen blood vessels, lower blood pressure, narrow or swell the airways, and affect the skin, digestive tract, and other organs. Both allergic and less common non-allergic pathways can cause an anaphylactic reaction.

  • Foods such as peanuts, tree nuts, shellfish, milk, eggs, or other foods can trigger anaphylaxis.
  • Medications, including some antibiotics, pain medicines, and injectable treatments, can cause a reaction.
  • Insect stings from bees, wasps, hornets, or fire ants may trigger anaphylaxis.
  • Latex exposure can cause anaphylaxis in people who are sensitized to latex.
  • Exercise can trigger a reaction, sometimes in combination with a particular food or medicine.
  • Some reactions follow exposure to other substances or medical treatments.
  • In some cases, no definite trigger is identified, which is called idiopathic anaphylaxis.

Risk Factors

Risk Factors for Anaphylaxis

  • A previous anaphylactic reaction increases the risk of another episode.
  • A known severe allergy to a food, medicine, insect venom, or latex raises the risk after future exposure.
  • Asthma, especially when poorly controlled, may increase the risk of severe breathing problems during a reaction.
  • Mast cell disorders can make severe allergic reactions more likely.
  • Certain cardiovascular conditions may increase the danger of low blood pressure during anaphylaxis.
  • Some medicines and underlying health conditions may affect the severity or treatment of a reaction.
  • Avoidable exposure to a known trigger increases the chance of another reaction.
  • Not carrying prescribed epinephrine can delay first-line treatment.
  • Delaying epinephrine or emergency care can allow anaphylaxis to become more severe.

Complications

Complications of Anaphylaxis

  • Airway obstruction can prevent air from reaching the lungs.
  • Respiratory failure can occur when breathing cannot provide enough oxygen.
  • Anaphylactic shock can cause dangerously low blood pressure and poor blood flow to organs.
  • Cardiac arrest can occur when the heart stops pumping effectively.
  • Brain and organ injury can result from prolonged lack of oxygen or circulation.
  • Death can occur if severe anaphylaxis is not treated promptly.

A biphasic reaction occurs when symptoms return after they initially improve, sometimes without a new exposure to the trigger. This is why emergency observation is important after treatment, even when a person feels better. The treating team will decide how long observation should continue based on the reaction and response to care.

Diagnosis

How Anaphylaxis Is Diagnosed

Clinicians diagnose anaphylaxis mainly by assessing the sudden pattern of symptoms, how quickly they began, possible exposure to a trigger, and the response to epinephrine. They ask about skin or mucosal changes, breathing, circulation, gastrointestinal symptoms, and other affected body systems. Treatment should not be delayed while waiting for a test, and symptoms may be assessed again after epinephrine.

  • Vital signs are checked, including breathing rate, oxygen level, pulse, and blood pressure.
  • A physical examination looks for airway, breathing, skin, circulation, and digestive findings.
  • The clinician asks about recent foods, medicines, insect stings, latex, exercise, and other possible exposures.
  • A serum tryptase test may be considered when it could help support the evaluation or identify an underlying mast cell condition.
  • The team assesses alternative diagnoses that can resemble anaphylaxis.
  • The response to epinephrine and other emergency treatment helps inform the overall assessment.

Treatment & Management

Anaphylaxis Treatment and Management

First-line treatment

Use epinephrine promptly

Epinephrine is the first-line treatment for suspected anaphylaxis. Use it without delay and do not wait for antihistamines or other medicines to work, because those medicines cannot replace epinephrine.

  • Emergency clinicians may give repeat epinephrine when symptoms continue or return and further treatment is clinically indicated.
  • Airway support may be needed if swelling makes it difficult to breathe.
  • Oxygen and other breathing support may be provided when oxygen levels or breathing are affected.
  • Intravenous fluids may be given to support blood pressure and circulation.
  • Antihistamines may help skin symptoms but are adjuncts and do not replace epinephrine.
  • Corticosteroids or other medicines may be used as additional treatment in selected situations.
  • Emergency observation helps monitor for persistent or returning symptoms.

After the reaction, follow-up may include referral to an allergy specialist, identification of likely triggers, and an individualized emergency action plan. People at risk should have access to prescribed epinephrine and receive training on when and how to use it. Follow-up after anaphylaxis can help review the event, update prevention steps, and prepare for future reactions.

Prevention

Preventing Anaphylaxis

  • Avoid confirmed triggers and ask healthcare professionals how to reduce accidental exposure.
  • Check food labels and ask about ingredients when eating food prepared by others.
  • Review medication labels and tell every healthcare professional about serious allergies.
  • Wear medical identification that lists important allergies.
  • Carry prescribed epinephrine and check its storage and expiration information as directed.
  • Share your emergency action plan with family, caregivers, school staff, or coworkers when appropriate.
  • Review the emergency plan regularly so others know how to respond.

An allergist may recommend testing when the trigger is unclear and may discuss supervised medication or venom desensitization in selected cases. Other individualized strategies depend on the suspected trigger, medical history, and risk of recurrence. Prevention can reduce risk but cannot eliminate every possibility of anaphylaxis.

Outlook and Prognosis

Outlook and Prognosis for Anaphylaxis

Many people recover when anaphylaxis is recognized and treated promptly with epinephrine and emergency care. Delayed epinephrine, severe breathing or circulation problems, and certain medical conditions can worsen the outcome. The seriousness of an episode varies, so every suspected reaction should be treated as an emergency.

A previous reaction increases concern for recurrence, but individualized evaluation and trigger management can reduce risk. Carrying prescribed epinephrine, knowing the emergency action plan, and being ready to use epinephrine promptly can reduce harm if another reaction occurs.

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