Severe Allergic Reaction (Anaphylaxis): Spotting It and Acting Fast

A severe allergic reaction can become life-threatening in minutes. A clear guide to recognising anaphylaxis, what to do immediately, and how people at risk can stay safe.

Most allergic reactions are mild — a rash, some sneezing, an itch. But occasionally an allergy triggers a severe, whole-body reaction called anaphylaxis that can become life-threatening within minutes. Knowing how to recognise it and act fast genuinely saves lives — for yourself, or someone around you. This is a clear, plain-language guide to spotting a severe allergic reaction and responding quickly.

What Causes It?

Anaphylaxis is a sudden, severe overreaction of the immune system to something the person is allergic to. Common triggers include certain foods (nuts, shellfish, eggs, milk), insect stings (bees, wasps), some medicines, and latex. It usually comes on quickly — within minutes to an hour of exposure. Someone can react even if past reactions were mild, which is why recognising the severe signs matters.

Warning Signs of a Severe Reaction

Signs of anaphylaxis — act immediately
  • Difficulty breathing, wheezing, or a tight throat / hoarse voice
  • Swelling of the lips, tongue, throat, or face
  • A widespread rash or hives with any of the above
  • Feeling faint, dizzy, or collapsing (a drop in blood pressure)
  • Sudden severe vomiting, tummy cramps, or a sense of "something is very wrong"

It is the breathing difficulty, throat/tongue swelling, or faintness/collapse that mark a reaction as severe and life-threatening — not just a rash on its own.

What to Do Immediately

  1. Call emergency services now (in India, 112 or 108) — say it is a severe allergic reaction. Do not wait to "see if it settles".
  2. If the person has an adrenaline auto-injector (such as an EpiPen), use it right away as they were instructed — it is the key emergency treatment for anaphylaxis.
  3. Help them sit up if breathing is hard, or lie down with legs raised if faint; do not stand them up suddenly.
  4. If there's an obvious trigger (like a bee sting), remove it if you safely can; stop any suspected medicine.
  5. Stay with them; if a second injector is available and symptoms persist after a few minutes, a further dose may be given as advised while waiting for the ambulance.
  6. If they stop breathing, be ready to start CPR (see our CPR guide).
Adrenaline first, and always go to hospital For anaphylaxis, the adrenaline auto-injector is the priority treatment — using it promptly is safe and can be life-saving; do not delay it for antihistamines, which are not enough for a severe reaction. And even if someone recovers after adrenaline, they must still go to hospital, because symptoms can return.

Living Safely With a Severe Allergy

  • Know your triggers and avoid them; read food labels and ask when eating out
  • Carry your adrenaline auto-injector at all times if prescribed — and make sure family/friends know how to use it
  • Consider a medical alert bracelet or card
  • Have an allergy action plan from your doctor, and check your injector's expiry

When to See a Doctor

A severe reaction is an emergency — call 112/108 immediately, every time. After any anaphylaxis, see a doctor (often referred to an allergy specialist) to identify the trigger, get an action plan, and be prescribed and shown how to use an adrenaline auto-injector. If you have known allergies or have had a worrying reaction before, do not wait for an emergency to plan — an online consultation is a good place to discuss your risk and next steps. Knowing the signs and acting fast is what saves lives here. (See our guides on skin allergies/hives, food allergy vs intolerance, and CPR.)

A note on sources General education based on trusted public health and allergy guidance (WHO, NHS). It does not replace an assessment by a doctor; anaphylaxis is a medical emergency — always call emergency services and use a prescribed adrenaline auto-injector.

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