Last updated:

Reviewed by:

Dr Bryony Henderson

, Lead GP at Livi

Medically reviewed

Anaphylaxis is a dangerous reaction to an allergen that can be life-threatening if not treated quickly. Learn what to do in case of anaphylaxis.

What is anaphylaxis?

Anaphylaxis is a sudden, dangerous reaction started by an allergic trigger. This reaction will quickly spread through the body and cause a medical emergency if not treated in the right way.

What are the symptoms of anaphylaxis?

The symptoms will develop quickly and get worse within minutes to hours:

  • Itching, hives or skin flushing

  • Red or itchy eyes

  • Swelling of the tongue or throat

  • Difficulty breathing, chest tightness or wheezing

  • A feeling of the throat closing

  • Diarrhoea

  • Dizziness or fainting

  • A rapid, slow or irregular heartbeat

  • Low blood pressure

  • Nausea or vomiting

  • Confusion and anxiety

  • A raised, itchy or red rash on the area of your skin that came into contact with the trigger

What causes anaphylaxis?

Anaphylaxis is a hypersensitivity reaction after exposure to a trigger, such as like: 

  • Foods, like nuts, milk, fish, shellfish, eggs, fruits

  • Medication, like antibiotics and aspirin

  • Insect stings

  • General anaesthetics

  • Dyes

  • Latex, which can be found in rubber gloves and condoms

This trigger confuses the body into thinking it’s highly dangerous and needs to be attacked. Your immune system releases histamines, which stimulate an inflammatory reaction.

As a result of this, the small blood vessels in the body, called capillaries, leak fluid into the surrounding tissue. This causes blood pressure to fall and reduced blood flow to the important organs of the body. 

This can lead to swelling of the throat, making it hard to breathe. It also causes blood vessels to widen, which results in a drop in blood pressure. This means less blood reaches the organs and tissues. To compensate, the body will release adrenaline to make the heart beat faster and stronger.

Adrenaline improves blood flow and causes the airways to widen. In a mild reaction, the adrenaline made by the body is enough to relieve the symptoms of anaphylaxis. 

If the reaction is severe, the airways will close and blood supply to the organs will reduce, making it difficult to breathe and get oxygen to the tissues, leading to suffocation and sometimes death.

How is anaphylaxis diagnosed?

If symptoms of anaphylaxis appear, especially within an hour after exposure to a trigger, there is no need for any more tests to diagnose this and you should start treatment as soon as possible.

More dangerous reactions often appear quicker than less severe ones, so you could be stung by a bee and the symptoms can take between a few minutes to a few hours depending on how allergic you are to the sting.

How to treat anaphylaxis

If you have any allergies, be aware of your trigger, as this could lead to anaphylaxis:

  • Confirm the trigger by getting an allergy test from your GP

  • Discuss any serious reactions with your GP as it may be best to see an allergy specialist for confirmation

  • Avoid any contact with the trigger as best as you can

  • Carry 2 in-date adrenaline auto-injectors at all times and use them whenever you think you may be experiencing anaphylaxis

If you think you or another person has symptoms of anaphylaxis, you need treatment as soon as possible – it could be life saving. Follow these steps:

  • Use an adrenaline auto-injector. If the person has one of these, look for instructions on the side of the injector before using it. Epinephrine (the medicine in auto-injectors) is the most effective treatment for anaphylaxis, and it works best when given as soon as possible.

  • Call 999 or emergency medical services. Ask for an ambulance and tell the operator the person has anaphylaxis. Always call an ambulance, even if the person is starting to feel better. Symptoms can return a few hours after the initial attack, sometimes catching people off guard.

  • Lie the person down and raise their legs. If they’re having difficulty breathing, sit them up straight until their breathing improves. If they’re pregnant, lie them down on their left side.

  • Remove the cause (if possible). For example, as long as it doesn’t put the person or you in further danger, you could try to remove the stinger from the skin after a bee sting.

  • Give another adrenaline auto-injection if their symptoms don’t improve after 5 to 15 minutes.

  • Start CPR if it’s needed. If the person’s breathing or heart stops, immediately start CPR until help arrives.

  • Keep track of what’s happened. Tell the paramedics or hospital staff what medication you’ve given to someone. Make sure you tell them if there’s no auto-injector available.

Even after successful treatment, some younger patients will get a recurrence of this reaction about 10 hours after the first episode, so children are usually kept in the hospital to make sure this does not happen.

When should I seek help?

Over half of deaths from anaphylaxis happen within the first hour from the first symptom, so quick action could save ayour life. If you are aware about coming into contact with a trigger and you start to get any symptoms of anaphylaxis within minutes to a few hours, you should seek help and start the treatment steps as soon as possible, even if you are still unsure of the reaction.

Last updated:
Reviewed by:
Dr Bryony Henderson, Lead GP at Livi