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Anaphylaxis
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Immune System

Anaphylaxis

Anaphylaxis is a serious, potentially life-threatening allergic reaction that can occur rapidly and affect multiple organ systems.

Overview

Anaphylaxis is a serious allergic reaction that can begin very quickly. The most common causes include reactions to foods (especially peanuts), medications, and stinging insects. Other causes include exercise and exposure to latex, though sometimes no cause can be found.

Symptoms

Anaphylaxis can affect many organs throughout the body:

  • Skin: Itching, hives, redness, swelling
  • Nose: Sneezing, stuffy nose, runny nose
  • Mouth: Itching, swelling of the lips or tongue
  • Throat: Itching, tightness, trouble swallowing, swelling of the back of the throat
  • Chest: Shortness of breath, coughing, wheezing, chest pain or tightness
  • Heart: Weak pulse, passing out, shock
  • Gastrointestinal tract: Vomiting, diarrhea, cramps
  • Nervous system: Dizziness or fainting

Management

If someone is having a serious allergic reaction, call 911. If an auto-injector is available, give the person the injection right away.

Frequently Asked Questions

Inject the epinephrine auto-injector into the outer thigh, even through clothing, and hold it in place for the time specified by the device manufacturer, usually 3 to 10 seconds. Immediately after injection, call emergency services or have someone else call 911, even if symptoms improve. Epinephrine is a temporary measure, and symptoms can return (biphasic reaction), so you must be monitored in a hospital setting for at least 4 to 6 hours. Do not wait to see if the reaction resolves on its own.
Yes, anaphylaxis can occur in people with no prior history of allergies, although it is less common. In adults, the most frequent triggers are medications (such as antibiotics, NSAIDs, or contrast dyes used in imaging), insect stings, and foods. Other less common triggers include latex, exercise-induced anaphylaxis, and idiopathic anaphylaxis where no cause is ever identified. If you experience a severe allergic reaction, keep a record of everything you consumed or were exposed to in the preceding hours to help identify the culprit.
naphylaxis usually begins within minutes of exposure to the trigger, though it can sometimes take up to an hour. The earliest warning signs often involve the skin and respiratory system, such as sudden itching, hives, or swelling of the lips and tongue. Respiratory symptoms like a tight throat, hoarseness, or difficulty breathing are critical red flags. If you experience any combination of skin changes and respiratory or gastrointestinal distress after a known allergen exposure, treat it as a medical emergency.
Most symptoms of anaphylaxis begin to improve within 5 to 15 minutes after epinephrine administration. However, the effects of epinephrine wear off after about 10 to 20 minutes, which is why a second dose may be necessary if symptoms persist or worsen. During recovery, you may feel weak, anxious, or have a rapid heart rate. You must remain under medical observation for several hours because a biphasic reaction, where symptoms return without re-exposure to the allergen, can occur in up to 20% of cases, typically within 4 to 8 hours.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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