Anaphylaxis

Anaphylaxis is a severe allergic reaction that can come on very quickly and may threaten life. You may also hear it called anaphylactic shock.

The signs of anaphylaxis include:

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

Anaphylaxis should always be treated as a medical emergency. If adrenaline is available, an injection of this medicine should be given as soon as possible.

Some people who have had anaphylaxis before carry an adrenaline auto-injector.

The injection goes into the outer thigh muscle, and the device should be held in place for 5 to 10 seconds. Instructions for using these auto-injectors are printed on the side of each device.

You should call 999 for an ambulance whether adrenaline has been given or not.

If the person still feels unwell after 5 to 10 minutes, give a second injection in the opposite thigh.

A second dose may also be needed if the person gets better and then becomes unwell again.

The person should lie flat with their legs raised on a chair or a low table. If they are having difficulty breathing, they should sit up instead, because that makes breathing easier.

If the person is unconscious, move them into the recovery position (on their side, supported by one leg and one arm, with the head tilted back and the chin lifted). If their breathing or heart stops, cardiopulmonary resuscitation (CPR) should be performed.

Further treatment will be carried out in hospital.

You can read more about treating anaphylaxis.

Anaphylaxis happens when your body's immune system overreacts to a substance that is actually harmless, such as a food. Substances that set off allergic reactions like this are called allergens.

The reaction usually starts within minutes of contact with the allergen. Sometimes, though, it can come on up to 4 hours later.

The triggers reported most often are:

• insect stings, particularly wasp and bee stings
• peanuts and tree nuts
• other foods, such as milk and seafood
• certain medicines, such as antibiotics

If you know what has triggered your anaphylaxis, take steps to avoid coming into contact with similar triggers.

You should be referred to a specialist allergy clinic. There you can find out what sets off your reaction, or, if you already know the cause, get further assessment and advice on how to avoid allergens in future.

You may be given two adrenaline auto-injectors to use if you have another episode of anaphylaxis.

Read more about preventing anaphylaxis.

Anaphylaxis is not common, but it can affect people of any age. Those most at risk are people who already have other allergic conditions, such as asthma or atopic eczema (an allergic skin condition).

The condition is life threatening, though deaths are rare. There are around 20 deaths in the UK each year. Most people make a full recovery if they get prompt and proper treatment.

Anaphylaxis comes from a problem with the immune system, which is the body's natural defence against illness and infection.

In anaphylaxis, your immune system overreacts to a substance that is actually harmless. It releases a number of different chemicals, such as histamine, to deal with a threat that isn't really there.

Wasp and bee stings cause most cases of anaphylaxis, though almost any insect bite or sting can set it off. Around 1 in 100 people are estimated to have an allergic reaction after a wasp or bee sting, but only a small number of them go on to develop severe anaphylaxis.

More than half of all cases of food-related anaphylaxis are caused by peanuts. Other foods known to trigger anaphylaxis include:

• nuts, such as walnuts, cashew nuts, almonds, brazil nuts and hazelnuts
• milk
• fish and shellfish
• eggs
• some types of fruit, such as bananas, kiwi fruit, grapes and strawberries

A small number of people develop anaphylaxis after taking certain medicines. These include:

• antibiotics, particularly penicillin-like antibiotics
• general anaesthetic, meaning the muscle-relaxant medicines used during surgery
• non-steroidal anti-inflammatory drugs (NSAIDs), a type of painkiller that includes ibuprofen and aspirin

People who are sensitive to these medicines usually react as soon as they begin a course of treatment, even if they have taken them safely in the past.

The risk of anaphylaxis from these medicines is very small, so in most cases the benefits of treatment outweigh the possible risk. To give you an idea, the risk of developing anaphylaxis is around:

• 1 in 1,480 after taking a NSAID-type painkiller
• 1 in 5,000 after taking penicillin
• 1 in 10,000 after being given a general anaesthetic

Contrast agents are a group of special dyes used in some medical tests to help certain areas of your body show up better on scans such as X-rays. A contrast agent injected into a blood vessel, for example, helps show up any problems in the vessel, such as a blockage, on the X-ray. This is known as angiography.

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

Fewer than 1 in 100 people have a natural rubber latex allergy. It is more common in people who work in healthcare, hair and beauty, catering and the motor industry.

You are also more likely to be affected if you have a history of hayfever, asthma or eczema, or certain medical conditions such as spina bifida.

Sometimes doctors test thoroughly and still can't find what set off an anaphylaxis episode. The cause stays unknown. When this happens, the condition is called idiopathic anaphylaxis.

If you think someone is having an anaphylaxis reaction, use an adrenaline injector straight away if one is available. Then dial 999 immediately afterwards.

If there is no adrenaline injector, call 999 straight away.

If you can see what may have triggered the reaction, such as a wasp or bee sting stuck in the skin, carefully remove it.

Adrenaline narrows the blood vessels, which raises your blood pressure and reduces swelling. It also opens the airways, so breathing becomes easier.

Give an adrenaline injection as soon as you suspect a serious reaction. The signs of suspected anaphylaxis are:

• problems breathing
• feeling faint or dizzy
• loss of consciousness

The person with anaphylaxis can give the injection themselves. Sometimes another person will need to do it, for example if it's a young child or someone who is unconscious.

Make sure you know what to do before you attempt the injection. When you, or the person you are responsible for, are first prescribed the injector, read all of the instructions carefully.

After injecting, hold the syringe in place for 5 to 10 seconds. You can give the injection through clothing.

Once you have injected the adrenaline, dial 999 for an ambulance straight away, even if the person is starting to feel better.

Most people improve quickly once the adrenaline has been used. If there's no improvement after 5 to 10 minutes, inject a second dose of adrenaline, if one is available. Inject it into the opposite thigh.

There are 2014 guidelines from the Medicines and Healthcare products Regulatory Agency (MHRA) on how to use an adrenaline auto-injector. You can read them as a PDF (188kb).

In most cases, a person with anaphylaxis should lie flat, with their legs raised on a chair or a low table. This helps keep blood flowing to the head and heart.

Pregnant women should lie down on their left side, so there's no extra pressure on the large vein that leads to the heart.

If the person is conscious but having trouble breathing, they should sit up. That makes breathing easier.

If the person is unconscious, check that their airways are open and clear, and check their breathing too. Then put them in the recovery position, so they don't choke on their vomit.

To do this, place the person on their side and make sure 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.

Even if adrenaline has been given, the person with anaphylaxis will need to go to hospital for observation, usually for 6 to 12 hours, because symptoms can occasionally return during this time.

In hospital, an oxygen mask can be used to help breathing. Fluids given through an intravenous drip, straight into a vein, can help raise blood pressure.

Along with adrenaline, other medicines such as antihistamines and corticosteroids can be used to help relieve symptoms. Blood tests may also be done while you're in hospital to confirm anaphylaxis.

You should be able to leave hospital once the symptoms are under control and it's thought they won't return quickly. That may be after a few hours, but if the symptoms were severe, you may have to stay for a few days.

The doctors may ask you to take antihistamine and corticosteroid tablets for 2 to 3 days after you leave hospital, to help stop your symptoms coming back.

A follow-up appointment will probably be arranged, so that you can be given advice on how to avoid further episodes of anaphylaxis.

You may also be given an adrenaline auto-injector for emergency use in the time between leaving hospital and attending that follow-up appointment.

Your doctor should refer you to a specialist allergy clinic for tests to find out what caused the anaphylaxis. Once you know which allergen set off the reaction, you can avoid it and lower the chance of another episode of anaphylaxis.

These are some of the tests commonly used to find out what you're allergic to:

• a skin prick test: your skin is pricked with a tiny amount of a suspected allergen, to see if it reacts by becoming red, raised and itchy
• a blood test: a sample of your blood is taken to see how it reacts to a suspected allergen

Your doctor may prescribe an adrenaline auto-injector if you've had an episode of anaphylaxis before and there's a risk of another one in future.

There are 3 types of auto-injector:

• EpiPen
• Jext
• Emerade

Each type is slightly different, so make sure you know how to use yours correctly. You can also ask for a "trainer" kit, which lets you practise giving injections to yourself or your child.

These points matter:

• Carry your auto-injector(s) with you at all times, with no exceptions. You may also be advised to get an emergency card or bracelet that gives full details of your allergy and your doctor's contact details, so that others know what is happening.
• Extremes of heat can make adrenaline less effective, so don't leave your auto-injector in the fridge or in your car's glove compartment.
• Check the expiry date regularly. An out-of-date injector will offer limited protection.
• The manufacturers offer a reminder service, where they contact you near the expiry date. The information leaflet that comes with your medicine has more details.
• If your child has an auto-injector, they will need to change to an adult dose once they reach 30kg (approximately 4.5 stone).
• Don't delay injecting yourself if you think you may be at the beginning of anaphylaxis, even if your first symptoms are mild. It's better to use adrenaline early and then find out it was a false alarm than to wait until you're sure you are having severe anaphylaxis.

You can lower the chance of coming into contact with a food allergen by doing a few simple things:

• checking food labels
• telling the staff at a restaurant what you're allergic to, so it's left out of your meal
• remembering that some foods may contain small traces of possible allergens (for example, some sauces contain wheat and peanuts)

You can lower your risk of being stung by an insect if you take a few basic precautions, such as:

• moving away slowly from wasps, hornets or bees and not panicking (don't wave your arms around or swat at them)
• using an insect repellent if you spend time outdoors, particularly in the summer

Some specialist allergy centres also offer a special treatment to help desensitise you to insect stings if you are at a particularly high risk of a further sting. A beekeeper or a gardener, for example, may be in this position.

If you're allergic to certain types of medicines, there are normally other medicines that can be used safely. For example, if you're allergic to:

• penicillin, you can normally take a different group of antibiotics known as macrolides
• non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and aspirin, you can normally take paracetamol safely. But read the ingredients of things like cold medicines carefully, to make sure they don't contain NSAIDs
• one type of general anaesthetic, others are available, or it may be possible to do the surgery using a local anaesthetic or an epidural injection
• angiotensin-converting enzyme (ACE) inhibitors, other blood pressure medicines, such as calcium channel blockers, can be used

Always tell any doctor, nurse or other health worker about the medicine allergies you have, as they may not be aware of them.

Sometimes a doctor has to use contrast agents even when there's a risk of anaphylaxis. Bleeding inside your brain is one example.

In that situation, you can be given injections of antihistamines and corticosteroids before the contrast agents. These may help stop symptoms from happening, or at least make them less severe.