Key points
- Treat anaphylaxis on clinical grounds; never wait to prove an IgE mechanism.
- Up to 10–20% of episodes have no hives or other skin signs.
- IM epinephrine 0.01 mg/kg of the 1 mg/mL solution into the mid-anterolateral thigh, maximum 0.5 mg per dose.
- Repeat epinephrine every 5–15 minutes if symptoms persist.
- A 20-kg child gets 0.2 mg = 0.2 mL of 1 mg/mL epinephrine; a teen of 25 kg or more uses the 0.3 mg autoinjector.
- Large local sting reactions grow for 24–48 hours and need antihistamine and cold compresses, not antibiotics.
- Systemic venom reactions beyond the skin → venom testing at least 4 weeks after the sting → subcutaneous venom immunotherapy.
Recognize anaphylaxis
Anaphylaxis is likely when symptoms start within minutes to a few hours of a likely trigger and involve 2 or more body systems, or when blood pressure falls or the airway is involved after a known allergen.
Skin signs are common but not required. A child who wheezes and vomits after eating peanut, with no hives, still has anaphylaxis.
The mechanism does not change emergency care. IgE, direct mast-cell release and unknown triggers are all treated the same way, at once.
| System | Typical findings |
|---|---|
| Skin and mucosa | Hives, flushing, itching, swelling of lips, tongue or uvula |
| Airway and lungs | Hoarse voice, stridor, throat tightness, wheeze, cough, low oxygen |
| Gut | Crampy abdominal pain, repeated vomiting, diarrhea |
| Circulation | Low blood pressure for age, fainting, pallor, floppiness in infants |
Epinephrine: dose, route and repeats
Antihistamines and corticosteroids are second-line. They help itch and hives but do not treat airway swelling or shock, and they do not reliably prevent biphasic reactions. Never let them delay epinephrine.
- Drug: epinephrine 1 mg/mL (1:1,000) intramuscularly into the mid-anterolateral thigh.
- Dose: 0.01 mg/kg, maximum 0.5 mg per dose. Example: 20 kg → 0.2 mg = 0.2 mL.
- Autoinjectors: 0.1 mg for about 7.5–15 kg, 0.15 mg for about 15–25 kg, 0.3 mg for 25 kg and above.
- Repeat every 5–15 minutes if symptoms persist or return.
- Lay the child flat with legs raised (or sitting up if breathing is hard); give oxygen and an IV fluid bolus for low blood pressure.
- Not responding after 2–3 doses: start an IV epinephrine infusion in a monitored setting.
Biphasic reactions, observation and discharge
A biphasic reaction is a return of symptoms after full recovery, usually within 12 hours, with no new exposure.
- Higher risk: a severe first reaction, needing more than one epinephrine dose, epinephrine given more than 60 minutes after onset, a wide pulse pressure, or an unknown trigger.
- Observe longer (often up to 6 hours or more) after a severe reaction or when more than one dose was needed.
- At discharge: 2 epinephrine autoinjectors, a written anaphylaxis emergency plan, teaching on when and how to use them, and referral to an allergist.
- Teach families to give epinephrine first and then call 911.
Exercise-induced anaphylaxis and cofactors
Some teens react only when exercise follows a trigger food (food-dependent exercise-induced anaphylaxis) or when a cofactor lowers the threshold.
Common cofactors are NSAIDs, alcohol, infection and heat. Advise no NSAIDs for 24 hours before exercise, no exercise for several hours after the trigger food, exercising with a partner, and carrying epinephrine.
Insect stings: local or systemic?
Venom immunotherapy is given subcutaneously. It sharply lowers the risk of a future systemic sting reaction and usually continues for 3–5 years. Testing done earlier than 4 weeks after the sting can be falsely negative.
| Reaction | What it looks like | Management |
|---|---|---|
| Large local reaction | Swelling around the sting, often over 10 cm, that grows for 24–48 hours and lasts up to a week; no fever or red streaks | Oral antihistamine, cold compresses, sometimes a short oral steroid; no antibiotics; venom testing not needed |
| Systemic skin-only reaction (child) | Hives or flushing away from the sting, no airway, breathing or blood pressure signs | Epinephrine plan; venom immunotherapy usually not needed in children |
| Systemic reaction beyond the skin | Wheeze, throat swelling, low blood pressure or other organ signs | Epinephrine; venom skin or IgE testing at least 4 weeks after the sting; venom immunotherapy if positive |
Common questions
What is the epinephrine dose for anaphylaxis in a child?
0.01 mg/kg of 1 mg/mL epinephrine IM into the outer thigh, maximum 0.5 mg, repeated every 5–15 minutes if needed. Autoinjectors come as 0.1, 0.15 and 0.3 mg.
Can you have anaphylaxis without hives?
Yes. Some children have only breathing, gut or blood pressure symptoms after a trigger. Treat with epinephrine anyway.
How long should a child be watched after anaphylaxis?
Until symptoms have fully resolved; longer, often 6 hours or more, after a severe reaction or when more than one epinephrine dose was needed.
Study this topic
Sources
- AAAAI/ACAAI Joint Task Force: Anaphylaxis, a 2023 practice parameter update (Ann Allergy Asthma Immunol)
- AAAAI/ACAAI: Anaphylaxis, a 2020 practice parameter update and GRADE analysis (J Allergy Clin Immunol)
- AAAAI/ACAAI: Stinging insect hypersensitivity, a practice parameter update 2016 (Ann Allergy Asthma Immunol)
- AAP: Guidance on completing a written allergy and anaphylaxis emergency plan (Pediatrics)
Written for Pedemy in our own words from the sources above; checked November 2026. For education only, not medical advice; check doses and local protocols before treating a patient. Pedemy is independent and not affiliated with or endorsed by the organizations cited.