Anaphylaxis and Severe Allergic Reactions

If you are experiencing a serious reaction or anaphylaxis, call 999 immediately.

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Anaphylaxis is a life threatening severe allergic reaction. It is a medical emergency, and requires immediate treatment. A severe allergic reaction can cause an anaphylactic shock and must be treated with an Adrenaline Auto Injector (AAI).

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What causes an anaphylactic reaction?

In most allergic reactions the resulting chemicals are released locally into the tissues in a particular part of the body (skin, eyes etc.). This means the symptoms of the allergic reaction usually only occur in this area.

In anaphylaxis, the chemicals that cause the allergic symptoms (e.g. histamine) are released into the bloodstream. The symptoms of anaphylaxis usually occur within minutes of exposure to the trigger substance (allergen) but sometimes an hour or so later.

The most common causes of anaphylactic reactions include:

  • Foods – including nuts, milk, fish, shellfish, eggs and some fruits
  • Medicines and drugs – including some antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin
  • Insect stings – particularly wasp and bee stings
  • General anaesthetic
  • Contrast agents – dyes used in some medical tests to help certain areas of your body show up better on scans
  • Latex – a type of rubber found in some rubber gloves and condoms.

In some cases, there’s no obvious trigger. This is known as idiopathic anaphylaxis.

Symptoms of anaphylaxis

Any or all of the following symptoms may be present during an anaphylaxis reaction:

  • Swelling of tongue and/or throat
  • Difficulty in swallowing or speaking
  • Vocal changes (hoarse voice)
  • Wheeze or persistent cough or severe asthma
  • Difficult or noisy breathing
  • Stomach cramps or vomiting after an insect sting
  • Dizziness / collapse / loss of consciousness (due to a drop in blood pressure) ( floppiness in babies).

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Preventing anaphylaxis

If you have a serious allergy or have experienced anaphylaxis before, it’s important to try to prevent future episodes.

The following can help reduce your risk:

Identify triggers

Finding out if you’re allergic to anything that could trigger anaphylaxis can help you avoid these triggers in the future.

If you’ve had anaphylaxis and have not already been diagnosed with an allergy, you should be referred to an allergy clinic for tests to identify any triggers.

The most commonly used tests are:

  • Skin prick test – your skin is pricked with a tiny amount of a suspected allergen to see if it reacts
  • Blood test – a sample of your blood is taken to test its reaction to a suspected allergen

Avoid triggers

If a trigger has been identified, you’ll need to take steps to avoid it in the future whenever possible.


You can reduce the chances of being exposed to a food allergen by:

  • Checking food labels and ingredients
  • Letting staff at a restaurant know what you’re allergic to so it’s not included in your meal. Allergy UK’s translation cards for eating out when travelling abroad are available via our Helpline.
  • Remembering some types of food may contain small traces of potential allergens – for example, some sauces contain wheat and peanuts
  • Identify any triggers – you may be referred to an allergy clinic for allergy tests to check for anything that could trigger anaphylaxis
  • Avoid triggers whenever possible – for example, be careful when food shopping or eating out if you have a food allergy
  • Carry two in-date adrenaline auto-injectors at all times – give yourself an injection whenever you think you may be experiencing anaphylaxis, even if you’re not completely sure

Insect stings

You can reduce your risk of being stung by an insect by taking basic precautions, such as:

  • Moving away from wasps, hornets or bees slowly without panicking – do not wave your arms around or swat at them
  • Using an insect repellent if you spend time outdoors, particularly in the summer
  • Being careful drinking out of cans when there are insects around – insects may fly or crawl inside the can and sting you in the mouth when you take a drink
  • Not walking around outside with bare feet

Some specialist allergy centres can also offer special treatment to help desensitise you to insect stings (immunotherapy).


If you’re allergic to certain types of medicines, there are normally alternatives that can be safely used.

For example, if you’re allergic to:

  • Penicillin – you can normally safely take a different group of antibiotics known as macrolides.
  • Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and aspirin – you can normally safely take paracetamol; read the ingredients of things like colds medicines carefully to make sure they do not contain NSAIDs
  • One type of general anaesthetic – others are available, or it may be possible to perform surgery using a local anaesthetic or an epidural injection.

Always tell any healthcare professional about medicine allergies you have, as they may not be aware of them.

Carry adrenaline auto-injectors

You may be prescribed an adrenaline auto-injector if there’s an ongoing risk you could develop anaphylaxis.

There are three types of auto-injectors – EpiPenJext and Emerade – that are each slightly different. Instructions are also included on the side of each injector if you forget how to use it or someone else needs to give you the injection.

It’s important to remember the following:

  • Carry 2 in-date auto-injectors at all times. There should be no exceptions; you may also be advised to get an emergency card or bracelet with full details of your allergy and doctor’s contact details to alert others
  • Make sure you and any carers know when and how to use your auto-injector – read the leaflet that comes with it and practise with a training device, which you can get from the manufacturer
  • Extremes of heat can make adrenaline less effective, so do not leave your auto-injector in the fridge or your car’s glove compartment, for example
  • Check the expiry date regularly and replace it before it expires. An out-of-date injector will offer limited protection
  • Manufacturers offer a reminder service, where you can be contacted near the expiry date – check the information leaflet that comes with your medicine for more information
  • Do not delay injecting yourself if you think you may be experiencing anaphylaxis, even if your initial symptoms are mild – it’s better to use adrenaline early and then find out it was a false alarm than delay treatment until you’re sure you’re experiencing severe anaphylaxis.

Treatment for anaphylaxis

You can find in-depth help on our anaphylaxis factsheet but here are the steps you need to follow if someone is having an anaphylactic shock:

  1. The first line treatment for severe symptoms is adrenaline (epinephrine) given by an injection into the upper outer muscle of the thigh. Adrenaline given in this way is a safe treatment and you should not hesitate to use it if required. It starts to work within minutes, reducing swelling, relieving wheeze and improving blood pressure.
  2. Do not wait to see if the symptoms clear up – call an ambulance immediately. All patients receiving emergency adrenaline should be transported to hospital for further care. Dial 999 and inform the controller that the patient is suffering from anaphylaxis.
  3.  Adrenaline is a short-acting drug and the effects will wear off quite quickly. If there is no response to the initial injection, current recommendations are to give a further adrenaline dose after 5 minutes.

If you are suffering from an anaphylactic shock, you should use your adrenaline pen immediately. While waiting for the ambulance, it is better if you lie down as this helps to maintain your blood pressure and avoids injury if you faint. You may be more comfortable with your shoulders raised a bit if you feel wheezy or short of breath.

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Positioning and resuscitation

Someone experiencing anaphylaxis should be placed in the correct position:

  • Most people should lie flat with their legs raised
  • If they’re pregnant they should lie on their left side
  • People having trouble breathing should sit up for a short time to help make breathing easier, and then lie down again when possible
  • Avoid a sudden change to an upright posture such as standing or sitting up – this can cause a dangerous fall in blood pressure

If the person’s breathing or heart stops, cardiopulmonary resuscitation (CPR) should be performed immediately.

In hospital

You will need to go to hospital for observation – usually for 6-12 hours – as the symptoms can occasionally return during this period.

While in hospital:

  • An oxygen mask may be used to help breathing
  • Fluids may be given directly into a vein to help increase blood pressure
  • Additional medicines such as antihistamines and steroids may be used to help relieve symptoms
  • Blood tests may be carried out to confirm anaphylaxis

You should be able to go home when the symptoms are under control and it’s thought they will not return quickly. This will usually be after a few hours, but may be longer if the reaction was severe.

You may be asked to take antihistamines and steroid tablets for a few days after leaving hospital to help stop your symptoms returning.

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