Anaphylaxis in babies: recognising a severe allergic reaction and what to do
What anaphylaxis is
Anaphylaxis is a severe, life-threatening allergic reaction that involves multiple body systems all at the same time. Unlike a mild allergic reaction, which might cause a rash on one part of the body, anaphylaxis causes simultaneous changes to the skin, airway, circulation, and gut. It develops rapidly, usually within minutes of exposure to a trigger. Without treatment, it can be fatal. With quick treatment, most people recover fully.
The key distinction from a mild reaction is the word "multiple". If your baby develops hives and their breathing also changes, or they vomit and become pale and floppy at the same time, that combination is the hallmark of anaphylaxis. Any single symptom involving the airway or circulation is also sufficient to trigger emergency action.
Common triggers in babies
The most common triggers for anaphylaxis in babies and young children are foods. According to Allergy UK and the AAP, the most frequent food allergens include peanuts, tree nuts (such as cashew and walnut), cow's milk, hen's egg, fish, shellfish, wheat, and sesame. In practice, peanut and tree nut reactions are among the most likely to cause severe reactions, although any food allergen can be serious in a sensitised child.
Other triggers include insect stings, particularly bee and wasp stings, and medications including antibiotics such as penicillin and non-steroidal anti-inflammatory drugs. Latex is a less common but known trigger. Sometimes no cause is identified, which is called idiopathic anaphylaxis, but this is less common in babies.
Knowing your baby's specific triggers and avoiding them is the foundation of management, but accidental exposures happen. Being prepared to act is what matters most.
Recognising the symptoms
Symptoms appear across several body systems and can progress from mild-looking to life-threatening within minutes. Here is what to look for:
Skin: Hives (raised, itchy welts), generalised redness and flushing, swelling especially of the face, lips, tongue, and around the eyes. The tongue or throat swelling can close the airway.
Airway and breathing: A hoarse or changed voice, a high-pitched sound when breathing in (called stridor), wheezing, coughing, throat tightness that your baby may show by clawing at their throat, and visible difficulty breathing. These are very serious signs.
Circulation: Becoming very pale, going limp, sudden loss of muscle tone, collapse, a racing or irregular heart rate, and loss of consciousness. These indicate the reaction is affecting the cardiovascular system.
Gut: Sudden cramping, vomiting, or diarrhoea. These symptoms alone are not anaphylaxis but are significant when they accompany other system involvement.
Brain: Confusion, sudden unusual drowsiness, loss of consciousness. If your baby is unusually hard to rouse after a potential allergen exposure, act immediately.
The NHS and the British Society for Allergy and Clinical Immunology define anaphylaxis as a severe, life-threatening, generalised or systemic hypersensitivity reaction. Clinical criteria are met when there is sudden onset involving either the skin or airway alongside either reduced blood pressure or evidence of organ dysfunction. In practice: if something feels very wrong after a food exposure and your baby is deteriorating, call 999.
Call 999 immediately
If you believe your baby is having anaphylaxis, call 999 right now. Do not wait to see if things improve. Tell the operator your location, your baby's age, and that you think they are having a severe allergic reaction. The operator will stay on the line with you.
While waiting for the ambulance, or while someone else calls, do the following.
Lay your baby flat on their back with their legs raised. Raising the legs helps blood flow to the vital organs when blood pressure drops. If your baby is having difficulty breathing and finds it easier to breathe sitting up slightly, allow them to sit up. Do not stand them up or allow them to walk. Do not leave them alone.
If an adrenaline auto-injector (such as an EpiPen or Jext) has been prescribed for your baby, use it now. Do not wait. Inject it into the outer mid-thigh. You can go through clothing. Press and hold for 10 full seconds, then remove. Adrenaline is the only first-line treatment for anaphylaxis. It works within seconds to minutes to reverse airway swelling and restore blood pressure.
If the first dose of adrenaline does not produce improvement within 5 to 15 minutes and you have a second auto-injector, use it. Always bring both injectors to the hospital.
What not to do
Do not give antihistamine alone as the primary or only treatment for anaphylaxis. Antihistamines such as cetirizine or chlorphenamine act on histamine receptors but do not act quickly enough to stop the life-threatening cascade of anaphylaxis. They can be given in addition to adrenaline, but they must not replace it or delay it.
Do not stand your baby up or carry them upright if they are in circulatory shock. Blood pressure is already low and standing can cause sudden cardiac arrest.
Do not assume the reaction has finished because symptoms have temporarily improved. Improvement after adrenaline is expected, but the reaction is not over.
Hospital observation is essential
Your baby must go to hospital after every episode of anaphylaxis, even if they respond well to adrenaline and seem fully recovered before the ambulance arrives. This is not optional.
The reason is biphasic anaphylaxis. In up to 20% of cases, symptoms return 1 to 72 hours after the initial reaction, without any further exposure to the allergen. This second wave can be as severe as the first. The NHS recommends a minimum of 6 hours of observation in hospital after a confirmed anaphylactic reaction. Children who had severe initial reactions may be kept for 12 to 24 hours.
At hospital, your baby will be monitored, may receive additional doses of adrenaline, corticosteroids, and antihistamine, and will be assessed for the need for an ongoing prescription for adrenaline auto-injectors.
After the episode: allergy investigation and planning
After your baby has recovered, ask for a referral to a paediatric allergist. The allergist will investigate the likely cause through skin prick tests or specific IgE blood tests. They will write an emergency action plan for your family and prescribe adrenaline auto-injectors, usually two, to carry at all times.
Avoid attempting elimination diets or at-home food challenges to identify triggers. Any food challenge in a baby with a history of severe reactions must be done in a supervised clinical setting.
Inform your nursery or childminder and make sure a copy of the action plan and a set of auto-injectors are kept there. Training for carers is available through Allergy UK and similar organisations.
Frequently asked questions
How quickly does anaphylaxis happen in babies?
Anaphylaxis usually develops within minutes of exposure to a trigger, though it can occasionally begin up to an hour later. Food-triggered reactions in babies typically start within 5 to 30 minutes of eating the food. The speed is one reason this is a medical emergency: symptoms can progress from mild to life-threatening in the time it takes to decide what to do.
What are the first signs of anaphylaxis in a baby?
Early signs often include sudden hives or flushing of the skin, swelling of the lips or face, and vomiting. Very quickly this can progress to throat tightness, difficulty breathing, or becoming pale and limp. If you see hives appearing alongside any breathing or behaviour change after a food exposure, treat this as a possible anaphylaxis and act immediately.
What is the difference between an allergic reaction and anaphylaxis?
A mild allergic reaction affects only one body system, for example hives on the skin with no other symptoms. Anaphylaxis affects two or more body systems at the same time, for example skin hives plus breathing difficulty, or sudden vomiting plus becoming pale and limp. Anaphylaxis is life-threatening. A mild rash alone is not, though it should still be reviewed by a doctor to assess allergy risk going forward.
Should I use an EpiPen or antihistamine first?
If your baby has been prescribed an adrenaline auto-injector and you believe they are having anaphylaxis, use the adrenaline immediately. Do not give antihistamine first and wait to see what happens. Antihistamines act far too slowly to stop anaphylaxis and are not appropriate as the sole or first treatment for a severe reaction. Adrenaline is the only first-line drug for anaphylaxis.
How do I use an EpiPen on a baby?
If an adrenaline auto-injector has been prescribed specifically for your baby by their allergy team, use it in the outer mid-thigh. You can inject through clothing. Remove the safety cap, press the tip firmly against the thigh until you hear a click, then hold in place for a full 10 seconds before removing. The 999 operator will guide you if you have never done it before. After use, keep the used device to hand it to the paramedics.
Do I need to go to hospital after anaphylaxis even if my baby seems better?
Yes, always. Your baby must go to hospital even if they have recovered after adrenaline. A biphasic reaction can occur hours later, where symptoms return without any further exposure to the allergen. NHS guidance recommends a minimum of 6 hours of monitoring in hospital after confirmed anaphylaxis. Do not drive home and wait and see.
Track your baby's health in one calm place
Cubby lets you log feeds, symptoms, and notes so you always have the information your doctor needs.
Start free