What is anaphylaxis?

Anaphylaxis is a severe and often sudden allergic reaction. It can occur when someone with allergies is exposed to something they are allergic to (known as an allergen). Reactions usually begin within minutes and rapidly progress, but can occur up to 2-3 hours later.

It is potentially life-threatening, and always requires an immediate emergency response.

What can cause anaphylaxis?

Common allergens that can trigger anaphylaxis are:


(e.g. peanuts, tree nuts, milk/dairy foods, egg, wheat, fish/seafood, sesame and soya)


(e.g. antibiotics, pain relief such as ibuprofen)


(e.g. rubber gloves, balloons, swimming caps)


(e.g. bee, wasp)

It is very unusual for someone with food allergies to have anaphylaxis without actually eating the food. Coming into contact with an allergen might trigger a local skin reaction, but is very unlikely to trigger anaphylaxis. However, if the allergen gets on to some food which the person then eats, this can then trigger a reaction.

The time it takes for a reaction to become severe varies, depending on the allergen:

  • Food: symptoms often begin immediately and may be mild, initially. Severe reactions can occur within minutes, but often develop around 30 minutes later. Severe reactions occasionally happen over 1-2 hours after eating – in particular, this has been reported  for milk – such reactions can mimic a severe asthma attack, without any other symptoms (e.g. skin rash) being present.
  • Insect stings: severe reactions are often faster, occurring within 10-15 minutes.

What are the symptoms of anaphylaxis?

Anaphylaxis usually develops suddenly, and gets worse very quickly. Symptoms include:


  • Persistent cough
  • Vocal changes (hoarse voice)
  • Difficulty in swallowing
  • Swollen tongue


  • Difficult or noisy breathing
  • Wheezing (like an asthma attack)


  • Feeling lightheaded or faint
  • Clammy skin
  • Confusion
  • Unresponsive/unconscious (due to a drop in blood pressure)

Usually, other less severe symptoms (such as an itchy, raised rash (hives), feeling or being sick, lip/face swelling, or stomach pain) are also present. However, sometimes, this does not happen and only severe symptoms are seen.

Why does anaphylaxis occur?

An allergic reaction occurs because the body’s immune system reacts to a substance that it wrongly perceives as a threat. The body produces an “allergy” antibody called Immunoglobulin E (IgE), which sticks to the substance (“allergen”) and causes the release of chemicals such as histamine. In the skin, this results in an itchy rash, swelling and flushing.

Many children (not just those with asthma) can develop breathing problems during an allergic reaction, similar to an asthma attack. The throat can tighten, causing swallowing difficulties and a high-pitched noise (stridor) on breathing.

How is anaphylaxis treated?

In severe cases, the allergic reaction can progress within minutes into a life-threatening reaction. The treatment of anaphylaxis is to give adrenaline, by an injection into the outer muscle of the mid-thigh (upper leg). Adrenaline treats both the symptoms of the reaction, and can also stop it from becoming worse. Other “allergy” medicines (such as antihistamines) can help with mild symptoms, but are not effective for severe reactions (anaphylaxis).

Giving adrenaline can be lifesaving, and should be administered at the first signs of anaphylaxis. Delays in giving adrenaline are a common finding in fatal reactions.

Anaphylaxis usually occurs together with more mild symptoms of an allergic reaction (such as an itchy mouth or skin rash), but can also happen on its own without any mild signs being present. Always give adrenaline FIRST (before other medicines such as inhalers) in someone with known food allergy who has sudden-onset breathing difficulties – even if there are no skin symptoms.

Some reactions require more than one dose of adrenaline; children can initially improve but then deteriorate. Always dial 999 and request an ambulance whenever anaphylaxis has occurred – even if there has been a good response to the adrenaline.

Outside hospital, adrenaline can be safely given by non-healthcare workers as an injection into the thigh muscle using an adrenaline auto-injector (AAI). Current brands available in the UK are EpiPen®, Emerade®, Jext®.

IF IN DOUBT, give adrenaline.


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