• Introduction
• Symptoms
• Causes
• Diagnosis
• Treatment
• Prevention
• Selected links
• Useful Article?

Introduction

Anaphylaxis (also known as anaphylactic shock) is an allergic condition that can be severe and potentially fatal. Anaphylaxis is your body’s immune system reacting badly to a substance (an allergen) such as food which it wrongly perceives as a threat. The whole body can be affected, usually within minutes of contact with an allergen but sometimes, the reaction can take place hours later. 

What are the symptoms?

The reaction is unpredictable and varies from mild itchiness and swelling to severe and life-threatening symptoms. 

If you have a severe anaphylactic reaction, you will experience a sudden drop in blood pressure and narrowing of the airways,which causes breathing difficulties and wheezing.

You will usually experience sudden swelling around the eyes, lips, genitals, hands, feet and other areas.

What triggers anaphylaxis?

Anaphylaxis can be triggered by a very wide range of foods and other substances. The most common food triggers include nuts, sesame seeds, fish, shellfish and eggs. Anaphylaxis can also be caused by an allergic reaction to wasp or bee stings, natural latex (rubber) and certain drugs such as the antibiotic penicillin.

Can it be prevented?

If you have had an anaphylactic reaction, doctors will perform some tests to find out what you are allergic to. Once you know the trigger, you can take steps to avoid it.

If you have a food allergy, be vigilant and check food labels for ingredients. If you are at a restaurant or buying takeaway food, ask if your food contains the allergen. A dietitian can advise you on how to exclude the allergen from your diet.

Symptoms

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.

Causes

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.

Triggers

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.

Foods

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

Medication

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.

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.

Diagnosis

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. These tests are often of a lower standard than those provided by the NHS or accredited private clinics 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.

Treatment

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 three 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.
• Jext. This works in much the same way as Anapen.

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.

Carefully reading the manufacturer’s instructions that come with your 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 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. 

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.

Prevention

Selected links

NHS Direct Wales links

Allergies

Angiodema

Food allergy

Indoor allergy

External links

Allergy UK

Foods Matter

Food Standards Agency

First aid advice – St Johns Ambulance