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Page last reviewed: 13/07/2011

Anaphylaxis is a severe, potentially life-threatening, allergic reaction that can affect many of the systems of the body, including:

  • airways
  • breathing
  • circulation (of the blood)

Anaphylaxis is also known as anaphylaxis shock.

Signs of anaphylaxis include:

  • breathing difficulties
  • dizziness
  • changes to your skin such as itchy skin or a raised red skin rash
  • swelling of certain body parts such as your lips, hands and feet (the medical term for this symptom is angioedema) 

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 anaphylaxis you should immediately dial 999 for an ambulance and tell the operator that you think anaphylaxis has occurred.

An injection of an anti-allergy medicine called adrenaline should be give as soon as a reaction is suspected. 

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.

If the person is unconscious, see if they are wearing an allergy alert bracelet which will say if they have an auto-injector.

Read more about the treatment of anaphylaxis.


Despite being potentially life-threatening, if treated promptly with adrenaline, most people will make a full recovery and experience no long term complications.Deaths due to anaphylaxis are rare in Ireland.

Causes and triggers

Anaphylaxis is your body's immune system overreacting badly to a substance such as food, which it wrongly perceives as a threat. Substances that provoke allergic reactions are known as allergens.

The whole body can be affected, usually 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; particualry peanuts
  • other types of foodstuffs such as milk and shellfish
  • 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 avoid further exposure to similar triggers.

Though in some cases this is not always possible (for example, wasp and bee stings), or when no obvious trigger can be found.

It is estimated that 1 in 12 people will go on to have another episode of anaphylaxis. Because of this risk you may be prescribed an auto-injector to use in the event of another episode.

Read more about preventing anaphylaxis

Who is affected

Anaphylaxis is an uncommon. It is estimated that only 1 in 1,300 people will develop the symptoms of anaphylaxis at some point during their life.

Anaphylaxis affects people of all ages and is slightly more common in females than males.

People with other allergic conditions, such as asthma or the allergic skin condition atopic eczema, are most at risk of developing anaphylaxis.

Immune system

The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.


An allergen is a substance that reacts with the body's immune system and causes an allergic reaction.


Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. Examples of antibiotics include amoxicillin, streptomycin and erythromycin.

Page last reviewed: 13/07/2011

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

If it was something you ate, such as peanuts, then 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 5-30 minutes.

Symptoms can vary in severity. Sometimes it can only cause mild itching or swelling, but in some people it can be extreme and lead to death.

Symptoms of anaphylaxis include:

  • a red raised itchy skin rash
  • swelling of your eyes, lips, hands and feet
  • narrowing of your airways which can cause breathing difficulties and wheezing
  • feeling like there is a lump inside your throat
  • a sudden drop in blood pressure which can make you feel faint and dizzy
  • nausea
  • vomiting
  • strange metallic taste in the mouth,
  • sore, red, itchy eyes
  • a feeling of impending doom like something terrible is going to happen

When to seek medical advice

If anaphylaxis is suspected you should check what systems of the body are being affected by symptoms. Most health professionals recommend a ABC method, where you should check:

  • Airways - are symptoms affecting the airways, such as swelling inside the throat
  • Breathing - are symptoms affecting breathing such as causing shortness of breath
  • Circulation - are symptoms affecting the circulation such as causing dizziness or fainting

If a person has symptoms affecting all three of these systems of the body then it is likely that a person has anaphylaxis; especially if they also have symptoms affecting their skin.

You should immediately dial 999 for an ambulance.


A fever, or high temperature, is when someone's body temperature goes above the normal 37°C (98.6°F). 
Wheezing is the whistling sound made during breathing when the airways are blocked or compressed.
Anxiety is an unpleasant feeling when you feel worried, uneasy or distressed about something that may or may not be about to happen.
An allergen is a substance that reacts with the body's immune system and causes an allergic reaction.

Page last reviewed: 13/07/2011

Anaphylaxis is caused by the immune system. The immune system protects your body from illness and infection by producing specialised cells called antibodies.

Antibodies identify potential threats, such as bacteria and viruses. They send signals to your immune system to release chemicals to destroy the threat and prevent the infection from spreading.

However, in the case of anaphylaxis, your immune system mistakes harmless proteins that are found in certain substances as a threat to your body and releases a wave of antibodies to defeat the supposed threat.

These antibodies in turn trigger the release of a number of different chemicals, such as histamine, and these chemicals can disrupt many of the functions of your body, such as:

  • widening of your blood vessels, which can cause a drop in your blood pressure
  • fluid build up in tissue which can cause swelling inside your throat and in your eyes, lips, genitals, hands and feet
  • the muscles you use for breathing can become more relaxed which can further contribute to your breathing difficulties

Exactly what causes your immune system to react in this harmful way is still unclear.


The most common triggers of anaphylaxis are:

  • insect stings
  • certain types of food
  • certain types of medication
  • contrast agents used in some types of medical scans (see below)

Insect stings

While any insect has the potential to trigger anaphylaxis the vast majority of cases are either caused by bee or wasp stings.

It is estimated that around 1 in 100 people will experience an allergic reaction after a bee or wasp sting, but only a small minority of these people will go on to develop 'full blown' anaphylaxis.


Peanuts are the leading cause of food-related anaphylaxis accounting for over half of all cases.

Other foods known to trigger anaphylaxis are:

  • other types of nuts, such as walnuts, almonds, brazil nuts, and hazel nuts
  • milk
  • fish
  • shellfish, such as lobster or crab

Less common food-related triggers include:

  • eggs
  • some types of fruit, such as bananas, grapes and strawberries


Types of medication known to trigger anaphylaxis in a small amount of people include:

  • antibiotics - particualry the penicillin group of antibiotics
  • medications that are used to put people to sleep before they have surgery (general anaesthetic)
  • the non-steroidal anti-inflammatory drugs (NSAIDs) type of painkillers, such as ibuprofen
  • angiotensin-converting enzyme (ACE) inhibitors - which is a medication that is used to treat high blood pressure

Most people who are sensitive to these types of medication will usually develop anaphylaxis as soon as they begin treatment.

The exception to this are ACE inhibitors as it has been known for people to take them for many years with no ill effects and then suddenly developing the symptoms of anaphylaxis.

The risks of these types of medication are very small so in most cases the benefits of treatment outweigh the potential risk. For example the risk of developing anaphylaxis:

  • after taking penicillin is around 1 in 5,000
  • after being given a general anaesthetic is around 1 in 10,000
  • after taking a NSAID type painkiller is around 1,480
  • after taking an ACE inhibitor is around 1 in 3,000

Contrast agents

Contrast agents are a group of special dyes that are used in certain medical tests as they can help certain areas of your body show up clearer on scans such as X-rays.

For example if it was thought that there was a problem with one of your blood vessels, such as a blockage, then a contrast agent can be injected into the vessel to help it show up clearly on the X-ray. This is known as an angiography.

The risk of developing anaphylaxis after being injected with a contrast agent is though to be less than 1 in 10,000.


Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
Blood vessels
Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessel are veins, arteries and capillaries.
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
An allergen is a substance that reacts with the body's immune system and causes an allergic reaction.
Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.

Idiopathic anaphylaxis

In as many as 1 in 4 cases of anaphylaxis no trigger can be identified despite extensive testing.

This type of anaphylaxis is known as idiopathic anaphylaxis.

Page last reviewed: 13/07/2011

A diagnosis of anaphylaxis is assumed by assessing what symptoms you have. Delaying treatment until a diagnosis has been confirmed would be too dangerous.

As mentioned in the symptoms section a confident diagnosis of anaphylaxis can usually be assumed if you have symptoms that are simultaneously affecting your:

  • airways
  • blood
  • circulation (of your blood)
  • skin

Once you are well enough to leave hospital you may be referred to an allergy clinic to indentify what was the substance, known as an allergen, which triggered the anaphyalixs.

The most widely used test to do this is to this is known as a RAST test. A sample of blood is removed and small samples of allergen, such as tiny pieces of peanut or shellfish, can then be placed into the sample of blood.

If your blood suddenly produces a high number of antibodies in reaction to the allergen this would normally indicate you were allergic to the allergen.

The use of commercial allergy testing kits is not recommended and they could trigger unpleasant symptoms such as a severe skin rash.

Also, allergy tests should be interpreted by a qualified professional who has detailed knowledge of your symptoms and medical history.


Blood tests
During a blood test, a sample of blood is taken from a vein using a needle so it can be examined in a laboratory.

Page last reviewed: 13/07/2011

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

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

An adrenaline injection must be given as soon as a serious reaction is suspected. If the person is carrying an adrenaline auto-injection kit, they may be able to inject themselves or you can help them to use it.

There are two types of auto-injectors:

  • EpiPen. This needle releases adrenaline when it is jabbed against the outer thigh.
  • Anapen. You hold the syringe against the outer thigh and push a button, which plunges the adrenalin-loaded needle into muscle.

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

After injecting, the syringe should be held in place for 10 seconds. The injections can be given through clothing.

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

If the person is unconscious, check their airways are open and clear and check their breathing. Then put them in the recovery position (see below).

Putting someone who is unconscious in the recovery position ensures that they do not choke on their vomit.

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

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 probably need to be admitted to hospital for observation for up to 24 hours as occasionally the symptoms can return a few hours later.

An oxygen mask can be used to help breathing and fluids given via an intravenous drip can help increase blood pressure.

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

Most people are well enough to leave hospital 1-3 days after being admitted.

You may be asked to take antihistamines and corticosteroid tablets 2-3 days after leaving hospital to help prevent a return of symptoms.

It is likely that you will be asked to attend a follow-up appointment so you can be given advice about how you can avoid having further episodes of anaphylaxis. Read more about the prevention of anaphylaxis. 


Adrenaline is a hormone produced at times of stress that affects heart rate, blood circulation and other functions of the body.
A drip is used to pass fluid or blood into your bloodstream through a plastic tube and needle that goes into one of your arteries or veins.
Inflammation is the body's response to infection, irritation or injury. It causes redness, swelling, pain and sometimes a feeling of heat in the affected area.
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Corticosteroid is a naturally occurring hormone produced by the adrenal gland or a synthetic hormone with similar properties. It is used to reduce inflammation, reducing swelling and pain.
Antihistamine medicine counteracts the action of histamine (a chemical released during an allergic reaction). Examples of antihistamines include loratadine and hydroxyzine.
The heart is a muscular organ that pumps blood around the body.
An allergen is a substance that reacts with the body's immune system and causes an allergic reaction.
Intravenous (IV) means the injection of blood, drugs or fluids into the bloodstream through a vein.

What does adrenaline do?

Adrenaline causes the blood vessels to constrict (become narrower), which raises your blood pressure and reduces swelling. It also causes the airways to open, relieving breathing difficulties, and suppresses the release of histamine.

Page last reviewed: 13/07/2011

Adrenaline auto-injectors

If you have experienced a previous episode of anaphylaxis it is likely you will be prescribed an adrenaline auto-injector.

A health professional should train you on how to use the auto-injector. You can also asked for a 'trainer' kit so you can practice giving yourself (or your child) injections.

The following points are important.

  • Carry your auto-injector at all times; there should be no exceptions. In some case, you may be recommended to carry multiple injectors. Check with your GP or the doctor in charge of your care. You may also be given an emergency card or bracelet with full details of your allergy and contact details of their doctor, to alert others. If so, wear this at all time.
  • Extremes of heat can make adrenaline less effective so do not leave your auto-injector in places such as your fridge or the glove compartment of your car.
  • Check the expiry date regularly. EpiPen has a shelf life of 18 months after the date of manufacture and Anapen has a shelf life of two years. An out-of-date injector will only offer limited protection.
  • The manufactures offer a reminder service where you can be contacted near the date of expiry. Check the information leaflet that comes with your medication for more information.
  • If your child has an auto-injector they will need to change over to an adult dose once they reach 30 kilos (4.7 stone). Depending on the shape and size of your child's body this could be anywhere between 5-11 years.
  • Do not delay in injecting yourself if you think you may be experiencing the beginning of anaphylaxis, even if your initial symptoms are mild. It is better to use adrenaline early and then find out it was a false alarm than delaying treatment until you are sure you are experiencing severe anaphylaxis.

Avoid triggers

If a trigger has been identified as being responsible for your episode of anaphylaxis then you will need to take steps to avoid it in future.


If the trigger was a foodstuff then taking some basic precautions should help you avoid the trigger in future. For example:

  • check the labels of any foods you eat
  • let staff know when booking at a restaurant
    remember that some types of food may
  • contain small traces of other food - for example, some sauces contain wheat and peanuts

Insect stings

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

  • if you encounter wasps, hornets or bees, move away from them slowly without panicking, do not wave your arms around or swat at them
  • use an insect repellent if you are planning to spend time outdoors, particularly in the summer
  • wear a long-sleeved top and long trousers, socks and shoes and avoid bright colours and strong perfumes or lotions
  • keep the windows of your car closed to stop insects getting inside


If you are allergic to certain types of medication then there are normally alternatives that can be safely used. For example, if you are allergic to:

  • penicillin you can normally safely take the erythromycin group of antibiotics
  • the non-steroidal anti-inflammatory drugs (NSAIDs) type of painkillers, such as ibuprofen you can normally safely take paracetamol
  • one type of general anaesthetic then there are others available; alternatively, it may be possible to perform surgery using a local anaesthetic or an epidural (where the lower section of your body is numbed)
  • to angiotensin-converting enzyme (ACE) inhibitors then alternative blood pressure medications such as calcium channel blockers can be used

Contrast agents

There may be times when it is necessary to use contrast agents even if places you at risk of anaphylaxis. For example, if you had a suspected emergency condition, such as bleeding inside your brain.

In such a circumstance you can be given injections of antihistamines and corticosteroids before the contrast agents as these medications may help prevent symptoms occurring or at least make the symptoms less severe.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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