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Anaphylaxis

Anaphylaxis is a severe, potentially life-threatening allergic reaction.

Anaphylaxis is a severe, potentially life-threatening allergic reaction that can develop rapidly.

It is also known as anaphylactic shock.

Signs of anaphylaxis include:

  • itchy skin or a raised, red skin rash
  • swollen eyes, lips, hands and feet
  • feeling lightheaded or faint
  • narrowing of the airways which can cause wheezing and breathing difficulties
  • abdominal pain, nausea and vomiting
  • collapse and unconsciousness

Read more about the symptoms of anaphylaxis.

What to do

Anaphylaxis should always be treated as a medical emergency.

If you suspect that you or somebody else is experiencing symptoms of anaphylaxis, you should immediately dial 999 for an ambulance.

If available, an injection of a medicine called adrenaline should be given if someone is having breathing difficulties, feeling faint, or has lost consciousness due to suspected anaphylaxis.

Some people with a previous history of anaphylaxis will have an auto-injector of adrenaline. This should be injected into their thigh muscle and held in place for 10 seconds. Instructions for how to use these auto-injectors can be found on the side of each device. 

If the person is conscious, you should place them in a position where they are comfortable and able to breathe easily until the ambulance arrives. If they are feeling faint, they should be laid flat with their legs elevated, if possible.

If the person is unconscious, you should place them in the recovery position (on their side, supported by one leg and one arm, with the head tilted back and the chin lifted).

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

Further treatment and observation will be carried out in hospital.

Read more about treating anaphylaxis.

Causes and triggers

Anaphylaxis is the result of your body's immune system overreacting to a harmless substance, such as food. Substances that provoke allergic reactions are known as allergens.

Anaphylaxis usually develops within minutes of contact with an allergen, though sometimes the reaction can happen hours later.

The most widely reported triggers of anaphylaxis are:

  • insect stings, particularly wasp and bee stings
  • nuts
  • other types of foods, such as milk and seafood
  • certain medications, such as some types of antibiotics

Read more about the causes of anaphylaxis.

Preventing further episodes

If you know what has triggered anaphylaxis, it is important to take steps to try to avoid further exposure to similar triggers.

If the cause of the allergic reaction is not known, you should be referred to a specialist allergy clinic where tests can be carried out to help identify possible triggers.

You may be provided with an adrenaline auto-injector to use during any future episodes of anaphylaxis.

Read more about preventing anaphylaxis.

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Anaphylaxis

The time it takes the symptoms of anaphylaxis to develop depends on how the trigger entered your body.

The time it takes for symptoms of anaphylaxis to develop depends on the cause.

If it was something you ate, such as peanuts, it can take anything from a few minutes to two hours. If it was something that entered your skin, such as a sting or an injection, it will usually take between five and 30 minutes.

Read more about the causes of anaphylaxis.

Allergic reactions can vary in severity. Sometimes they only involve mild itching or swelling, but in some people they can be severe and life-threatening.

Symptoms of anaphylaxis include:

  • itchy skin or a raised, red skin rash (hives)
  • swollen eyes, lips, hands and feet (angioedema)
  • feeling lightheaded or faint
  • narrowing of the airways which can cause wheezing and breathing difficulties
  • abdominal (tummy) pain, nausea and vomiting
  • collapse and unconsciousness

When to seek medical advice

If someone has the symptoms of anaphylaxis, they need urgent medical help, particularly if you know they have allergies.

You should immediately dial 999 for an ambulance.

Content Supplied by NHS Choices

Anaphylaxis

If you suspect that somebody is experiencing the symptoms of anaphylaxis, immediately call 999 for an ambulance.

If you suspect somebody is experiencing symptoms of anaphylaxis, call 999 immediately for an ambulance and tell the operator you think the person has anaphylaxis.

If you can see a potential trigger, such as a wasp or bee sting embedded in their skin, remove it.

If available, an adrenaline injection should be given as soon as a serious reaction is suspected. This can be done by the person with anaphylaxis if possible, but in some circumstances (such as cases involving a young child or someone who is unconscious) you may need to inject them yourself. 

Before attempting the injection, make sure you know the correct way to use the specific device available.

There are three types of auto-injectors:

  • EpiPen
  • Jext
  • Emerade

These auto-injectors release adrenaline when jabbed or pressed against the outer thigh.

Make sure you do not accidentally inject into a fatty part of their leg, as the adrenaline cannot move through fat. Also do not inject into a vein or artery, as this can cause dangerous side effects. The injector should only be placed firmly into the muscle of the outer thigh.

Carefully reading the manufacturer's instructions that come with the auto-injector will teach you how to do this. Make sure you read the instructions as soon as you are first prescribed an auto-injector.

After injecting, the syringe should be held in place for 5-10 seconds. Injections can be given through clothing.

Read MHRA (2014) guidelines on how to use an adrenaline auto-injector (PDF, 188Kb).

Most people should experience a rapid improvement in symptoms once the adrenaline has been used. If there is no improvement after five minutes, you should inject a second dose of adrenaline, if one is available. This should be injected into the opposite leg.

If the person has asthma and they have a reliever inhaler (usually blue), this should be used if they are wheezing.

Positioning and resuscitation

If the person is unconscious, check their airways are open and clear and also check their breathing. Then put them in the recovery position (see below) to ensure they do not choke on their vomit.

Place the person on their side, ensuring they are supported by one leg and one arm. Open the airway by tilting the head and lifting the chin.

If the person is conscious but experiencing trouble breathing, they may prefer to sit up as this will make breathing easier.

If the person is conscious but feels faint, they should lie flat with their legs elevated, if possible. They should not sit or stand as this could potentially lead to a heart attack.

If a woman is pregnant, they should lie down on their left side to avoid putting too much pressure on one of the large veins that leads to the heart.

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

Admission to hospital

Even if adrenaline is given, the person will need to be admitted to hospital for observation (usually for six to 12 hours) as occasionally symptoms can return during this period.

While in hospital, an oxygen mask can be used to help breathing and you may be given fluids via an intravenous drip (directly into a vein) to help increase your blood pressure.

As well as adrenaline, additional medications such as antihistamines and corticosteroids can be used to help relieve symptoms.

Blood tests may also be carried out while you are in hospital to confirm a diagnosis of anaphylaxis.

You should be able to leave hospital when the symptoms are under control and it is felt they will not quickly return. In some cases, this may be after a few hours, but there is a chance you will have to stay in hospital for a few days if the symptoms were severe.

You may be asked to take antihistamines and corticosteroid tablets two to three days after leaving hospital to help prevent a return of symptoms.

It is likely you will be asked to attend a follow-up appointment so you can be given advice about how you can avoid further episodes of anaphylaxis. You may also be given an adrenaline auto-injector for emergency use between leaving hospital and attending the follow-up appointment. 

Read more about preventing anaphylaxis

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