Q&A: Anaphylaxis - severe allergic reactions explained

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Media captionHow to spot potentially life-threatening allergic reactions and how to deal with them

What is anaphylaxis?

Anaphylaxis is a severe allergic reaction that may be life-threatening. It is rare but can affect anyone of any age.

People with asthma, eczema or hay fever may be at greater risk of developing the condition.

In anaphylaxis the body's immune system over-reacts to a normally harmless substance. This can happen straight after the person is exposed to the substance (which is known as an allergen) or can develop a few hours later.

The allergen triggers a rapid release of chemical substances in the blood - such as histamine. These in turn set off a cascade of reactions, causing a drop in blood pressure and swelling around the body. There are still many unanswered questions about why this overwhelming immune response occurs.

What triggers anaphylaxis?

Image copyright Science Photo Library
Image caption Allergies to nuts, fish and milk are more common in young people

Many different things can lead to an anaphylactic reaction.

These can include:

Food - peanuts, almonds, walnuts, cashews, Brazil nuts, fish, shellfish, dairy products and eggs

Insect stings - bee stings or wasp stings

Medication - such as some types of antibiotics

How can you tell if someone is having an anaphylactic reaction?

Image copyright Anaphylaxis Campaign
Image caption There may severe facial swelling and flushed skin

Symptoms vary and can develop quickly in any order.

An itchy, red rash may appear and spread across the body.

You may see swelling around the mouth, tongue, eyes or other parts of the face and body.

People can find it difficult to speak, swallow or breathe and may sound wheezy.

They may feel light-headed and nauseous.

In severe reactions people can lose consciousness.

What to do if you suspect someone is having an anaphylactic reaction

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Image caption Adrenalin can help reduce swelling and make it easier to breathe

Call 999 immediately and explain you suspect anaphylaxis.

If you can see an obvious trigger - for example peanuts or a wasp - move these substances away.

People with severe allergies are often prescribed auto-injector pens containing adrenalin (also known as epinephrine).

Adrenalin is a hormone which is produced naturally by the body during times of stress. When given during anaphylaxis it helps maintain an adequate blood pressure, allows the airways to relax so it is easier to breathe and reduces swelling.

If the allergic reaction is severe - for example, if the person is losing consciousness or is having difficulty breathing - the auto-injector should be given immediately.

The person having the reaction may have been trained to administer it themselves. If they are unable to do this - if they are young, or losing consciousness - you may need to help.

To give the adrenalin the tip of the pen should be injected into their thigh muscle and held in place for 10 seconds. There are further instructions on the side of the auto-injector.

They should be placed in the position that they find most comfortable and easiest to breathe in.

If they are feeling faint you may need to lie them flat and elevate their legs.

If the person stops breathing you need to start CPR.

What happens next?

Image caption Call an ambulance if you suspect anaphylaxis, even if the person has already taken adrenalin

Anyone suspected of having an anaphylactic shock must go to hospital. They will be monitored and treated.

People at the risk of anaphylaxis are often given an adrenalin auto-injector pen to carry with them at all times and may be referred to a specialist allergy clinic.

How dangerous is anaphylaxis?

Although the condition is life-threatening, deaths are rare. It is estimated that around 20-30 deaths occur in the UK each year.

Prompt treatment, with adrenalin auto-injectors, means most people make a full recovery.

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