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Anaphylactic shock can be life-threatening. Read our guide to familiarise yourself with the causes, symptoms & how it should be treated


Anaphylactic shock, also known as anaphylaxis, is a severe allergic reaction that can develop quickly. It can be life-threatening if not treated promptly, though with swift and proper treatment the vast majority of people affected make a full recovery. Anaphylactic shock occurs when your body’s immune system overreacts to a substance (a food or medicine, for example). Substances that trigger allergic reactions are known as 'allergens'.


Anaphylactic shock generally develops within minutes of exposure to an allergen. Anaphylaxis must be treated immediately, as leaving the condition untreated can be potentially fatal. 


What causes anaphylactic shock?


The most common causes of anaphylactic shock include:

• Insect stings, especially from bees and wasps

• Peanuts and tree nuts, including pecans, cashews and walnuts

• Other types of food, such as milk, shellfish and certain fruits

• Some medicines, for example, antibiotics, general anaesthetics (muscle-relaxant medicines used during surgery) and non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin


Other possible allergens include contrast agents (a group of dyes used in medical tests to help certain parts of your body show up more clearly on scans) or rubber latex.


If you experience anaphylactic shock and the trigger is unknown, this is referred to as 'idiopathic anaphylaxis'.


What are the symptoms of anaphylactic shock?


Anaphylaxis generally develops suddenly and worsens rapidly. Symptoms include:

• Difficulty in breathing – breathing may be fast and/or shallow, or there may be wheezing

• Feeling faint or lightheaded, or even collapsing and losing consciousness

• Damp, clammy skin

• A racing heartbeat

• Feeling anxious, disoriented or confused

• Other allergy symptoms (such as a rash, swelling, nausea or vomiting)


If you’re experiencing the rapid onset of any, or a combination, of the above symptoms, seek immediate medical attention.


What should you do if someone goes into anaphylactic shock?


Anaphylactic shock is a medical emergency and should be treated promptly. If someone is experiencing symptoms of anaphylaxis, you should:

• Use an adrenaline auto-injector if the person has one. Make sure you know how to use it first

• Call 999 for an ambulance – even if the person begins to feel better. Tell the operator that the person may be experiencing anaphylaxis

• Ask the person to lie down (unless they’re pregnant, unconscious or having breathing difficulties – you'll find information about what to do in those cases below)

• Remove the allergy trigger if you can

• If there is another auto-injector available, give a second injection five to 15 minutes later if their symptoms don’t improve


Treatments for anaphylaxis


Auto-injectors, positioning and resuscitation in hospital are used to manage a sudden attack of anaphylaxis.


People with severe allergies are often prescribed adrenaline auto-injectors to carry with them at all times. These can help stop an allergic reaction from escalating and becoming life-threatening. They should be used as soon as symptoms of anaphylaxis start. Learn more about them here.


Make sure you know how to use your type of auto-injector correctly. Instructions are included with each injector.


Someone experiencing anaphylaxis should be positioned comfortably. Most people are best off lying flat but there are some exceptions to this rule:

• If they are having breathing difficulties, they should sit up (with help if necessary) to make it easier for them to breathe

• Pregnant women should always be positioned lying down on their left side

• If someone is unconscious, they should be placed in the recovery position – this is part of basic first aid training

• Anyone standing or sitting up already should avoid suddenly changing their position


If the person’s breathing or heart stops, CPR should be performed immediately.


If you've experienced anaphylactic shock you should go to hospital for observation, even if your symptoms have subsided and appear to have resolved. They may want to keep you in for six to 12 hours, as sometimes symptoms can return.


You may be asked to take a medicine, such as antihistamine and steroid tablets, for a few days after your hospital visit. A follow-up appointment with an allergy specialist may be arranged to discuss how you can avoid further episodes of anaphylaxis.


How can anaphylaxis be avoided?


If you have a severe allergy, or have experienced anaphylaxis in the past, it’s important to do what you can to help prevent future episodes. The following can help reduce your risk:

• Establishing what your triggers are – an allergy clinic will carry out tests to check for these

• Avoiding triggers when you can do so – if you have a food allergy, make sure you always check the ingredients on packaging and be careful when dining out

• Always carrying an adrenaline auto-injector if you have been prescribed one. If you have two, try to always carry both with you


If you have an allergy or have had anaphylaxis before, visit your GP for advice. 


Next steps


• If you or someone you know is experiencing symptoms of anaphylactic shock, treat it immediately by using an adrenaline auto-injector, calling an ambulance, lying down flat and removing the trigger if possible

• Take the proper steps to prevent future episodes of anaphylaxis by visiting your GP for advice and/or for an allergy test, identifying and avoiding triggers, and carrying your adrenaline auto-injector

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