Anaphylaxis guide for healthcare professionals

Anaphylaxis is a severe and often sudden allergic reaction. It can occur when a person 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)

By far, the most common cause of anaphylaxis in children and young people is food allergy.

It is very unusual for someone with food allergies to experience anaphylaxis without actually eating the food: skin contact with an allergen is very unlikely to trigger anaphylaxis (but can cause contamination if handling food, which if eaten might 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 hives or urticaria, angioedema, nausea, vomiting or abdominal pain) are also present. However, in around 10% of severe reactions, this does not occur: the first symptoms are those of a severe reaction, often mimicking an asthma attack. For this reason, always consider anaphylaxis as a differential diagnosis in someone with known food allergy who has sudden-onset breathing difficulties – even if there are no skin symptoms.

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. Immunoglobulin E (IgE) is produced which sticks to the allergen, causing activation of cells such as mast cells which initiate an inflammatory cascade causing the release of mediators such as histamine. In the skin, this results in an itchy rash, swelling and flushing. Histamine is only one mediator involved – which is probably why antihistamines do not prevent anaphylaxis, and should not be used as first-line treatment.

How is anaphylaxis treated?

Allergic reactions can evolve within minutes into life-threatening reactions. The first line treatment for anaphylaxis is adrenaline (epinephrine), given by an injection into the outer mid-thigh muscle in the leg. Adrenaline treats both the symptoms of the reaction, and also helps stops the reaction by stabilising mast cells and other cells. Other “allergy” medicines (such as antihistamines) can help with mild symptoms, but are not effective for severe reactions (anaphylaxis).

Administration of adrenaline can be lifesaving. Some anaphylaxis reactions require more than a single dose of adrenaline; children can initially improve but then deteriorate later. It is therefore vital to always dial 999 and request an ambulance whenever anaphylaxis has occurred – even if there has been a good response to an adrenaline injection.

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

Delays in giving adrenaline are a common finding in fatal reactions.

Giving adrenaline can be lifesaving, and should be administered at the first signs of anaphylaxis.

IF IN DOUBT, give adrenaline.


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