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What is anaphylaxis?

01 Dec 2022

Find out all about this severe, extreme allergic reaction, including why it happens, common triggers and how to manage your condition safely

Written by Helen Foster on January 22, 2019 Reviewed by Prof Michael Rudenko on January 30, 2019

Allergies to peanuts, bee stings or sesame often make headlines as they can be incredibly dangerous. In those reports, anaphylaxis – or anaphylactic shock – are often mentioned, but do you actually know what those terms mean? Our guide explains all you need to know.

What is anaphylaxis?

Anaphylaxis is a very severe type of allergic reaction that can be life-threatening.

When any allergic reaction happens, your immune system sees a usually harmless substance as an invader and sets up a response designed to attack it by releasing a chemical called histamine from mast cells, which are activated by allergens, into the body. It’s this that triggers common allergy symptoms, like runny nose, rashes, or swelling. In a localised allergic reaction, this occurs just in the area affected by the allergen – so if you are allergic to pollen and it enters your nose or eyes, that’s where you get symptoms. But in anaphylaxis, the allergic reaction can happen all over the body – and this is what makes it dangerous and a medical emergency.1

What are the symptoms of anaphylaxis?

Symptoms include:2
  • reddening of the skin
  • a rash or swelling in the throat, tongue, lips, hands or feet
  • nausea and vomiting
  • fainting
Anaphylaxis becomes potentially dangerous if swelling occurs in the throat, mouth or tongue as this can impede breathing. An anaphylactic reaction can occur fast, just minutes after coming into contact with the substance you’re allergic to.3

What is anaphylactic shock?

This is a complication of an anaphylactic reaction. In anaphylactic shock, the person’s blood pressure falls very suddenly and the airways narrow. Signs of anaphylactic shock include:4
  • paleness of the skin or lips
  • wheezing or breathing problems
  • cough

Could any allergy cause anaphylaxis?

Theoretically, yes – a few isolated cases have been triggered by cardamom, goji berry and asparagus.5 However, these are unusual and rare – most cases of anaphylaxis are caused by a few specific allergies – for example bee and wasp stings. Allergies can be different in adults, children and babies. Food allergies most commonly linked to anaphylaxis include tree nuts, like peanuts or cashews, shellfish, while in children, it’s more usually eggs and dairy products.6 Latex, found in rubber products like condoms or rubber gloves is another common trigger, and certain medications, like penicillin, can also be a problem.7 If you have a bad or worsening reaction to any allergen, talk to your doctor about your risk of anaphylaxis.8 This is particularly important if you also suffer from asthma.  Anaphylactic reactions can be more serious for those with asthma.9

How can you manage anaphylaxis?

The first step is to have proper allergy testing to determine exactly what it is that you are allergic to. Your GP can arrange this for you.

Once you know your trigger, it’s critical that you learn how to avoid it. For example, you could:10
  • read labels carefully on food products
  • ask the chef in restaurants about ingredients in the dishes
  • tell doctors, dentists and other healthcare professionals if you have any medication allergies before treatment
  • cover exposed skin and avoid strong perfumes if you’re allergic to bee or wasp stings, and have special de-sensitisation treatment or immunotherapy

However, it’s definitely true that some triggers – such as insects – are harder to avoid. This means it’s important that anyone who has suffered an anaphylactic reaction in the past – or who might be at risk of one – carries at least two auto-injectors.

These are device containing the hormone adrenaline, which is usually released by the body during stress. A 2008 study by the World Allergy Organisation reported the following effects of adrenaline on anaphylaxis:11
  • airways open to ease breathing
  • blood vessels narrow, so blood pressure doesn’t fall dangerously low
  • heart is stimulated to beat strongly
  • itching, hives and swelling are reduced
You still need to see a doctor though – a condition called biphasic anaphylaxis can trigger a second attack within the next 72 hours so you should be observed for a short period.12  Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies


1. Tupper J, Visser S. Anaphylaxis. A review and update 2. Anaphylaxis Campaign. Signs and Symptoms

3. As above

4. Zawn Villines. Medical News Today. What are the symptoms of anaphylactic shock? 5. Worm W, et al. New trends in anaphylaxis

6. As Source 2
7. As Source 2
8. As Source 2
9. As Source 1

10. NHS. Prevention: Allergies 11. Kemp SF, et al. Epinephrine: The Drug of Choice for Anaphylaxis – A Statement of the World Allergy Organization 12. As Source 3