Anaphylaxis: sudden severe allergic reaction and emergency management

Common triggers

Typical causes are exposures to well-known allergens. These include foods (for example peanuts, tree nuts, shellfish), insect venom such as stings, and a variety of medications including some prescription and over-the-counter drugs. Reactions may begin after a person eats an allergen, breathes in an inhaled substance, or receives an injected exposure such as a vaccine or therapeutic drug. Some individuals react to latex or exercise in combination with food exposure. The trigger is often called the allergen.

Typical signs, course and diagnosis

Signs of anaphylaxis are varied. Skin findings are common (hives, flushing, itching). Respiratory problems may include wheeze, stridor and difficulty breathing. Throat tightness and swelling of the throat or tongue can interfere with the airway. Cardiovascular effects range from faintness to profound low blood pressure and shock. Gastrointestinal discomfort, rapid heartbeat and anxiety are also reported. Diagnosis is usually clinical based on the rapid onset of characteristic signs and symptoms; laboratory tests such as tryptase levels can sometimes support the assessment but are not required for immediate treatment. See more on diagnosis and evaluation.

Reactions may be IgE-mediated (classic allergic mechanism) or occur through non-IgE pathways that produce a similar clinical picture; historically the latter were called "anaphylactoid," but contemporary practice regards both as forms of anaphylaxis because treatment is the same. A biphasic response—return of symptoms hours after apparent recovery—can occur and is a reason for observation after initial treatment.

Treatment and first response

Immediate intramuscular administration of epinephrine (adrenaline) is the first-line, life-saving treatment for anaphylaxis and should be given as soon as anaphylaxis is suspected. Positioning the person flat with legs elevated (unless breathing is impaired), calling emergency services, and repeated epinephrine doses as advised are critical. Adjunctive measures in medical settings may include supplemental oxygen, intravenous fluids, inhaled bronchodilators, antihistamines and corticosteroids, but these do not replace epinephrine. Patients at risk should carry an epinephrine auto-injector and receive instruction on its use; medical providers may give guidance about avoidance and risk reduction.

Prevention focuses on identifying and avoiding known triggers, medical alert identification, and education for patients and caregivers. Because anaphylaxis can progress quickly, early recognition of warning signs and rapid treatment with epinephrine are the most important actions to reduce severe outcomes. For a general summary on allergic reactions and related resources see allergy information and a basic symptoms overview.

For clinicians and patients seeking further practical guidance, resources on recognition, emergency protocols and long-term management are available; brief educational materials often cover how to distinguish mild allergic reactions from life-threatening anaphylaxis and when to use emergency medication. See practical links on throat swelling, breathing difficulties, and monitoring for circulatory collapse after exposure. Additional clinical reference pages discuss detailed diagnosis and follow-up care and review the full range of possible signs and symptoms.

If you or someone you care for has experienced anaphylaxis, speak with a healthcare provider about personalized prevention plans, prescriptions for epinephrine, and training to respond quickly in an emergency.