Page reviewed by Dr Elena Salagean

What is anaphylaxis?

Anaphylaxis is a systemic severe, life-threatening allergic reaction that can occur rapidly after exposure to an allergen that has triggered an immune system reaction. Due to its systemic nature, it affects several body systems, including the respiratory, cardiovascular, and gastrointestinal systems. Together with rashes, hives, angioedema and other symptoms, it is the most serious type of allergic reaction in sensitised individuals.

What causes anaphylaxis?

Anaphylaxis can be caused by the same allergens that are capable of causing an allergic reaction

These include foods (nuts, shellfish, etc.), medications (antibiotics such as Penicillin, Aspirin and ACE Inhibitors such as Ramipril or Enalapril), insect stings (especially bees and wasps), chemicals such as latex and so on.

Idiopathic anaphylaxis is also a rare type of anaphylaxis that occurs with no identifiable cause. In such cases, the anaphylaxis symptoms are triggered without anything external to the body triggering them.

In anaphylaxis, the immune system reacts to an allergen by reducing several pro-inflammatory chemicals that ultimately causes the body to go into shock.

What are the symptoms?

The symptoms of anaphylaxis can be very severe as they occur at a whole body level. Unlike a rash which only affects the skin, anaphylaxis affects multiple body systems from top to bottom.

Some symptoms of anaphylaxis include:

  • Respiratory system: Difficulty breathing, rapid breathing, wheezing, feeling of throat tightening and shortness of breath
  • Skin: Itchy, urticarial rash with hives and wheals spreading all over the skin. Swelling of the face, lips, tongue and throat also occurs.
  • Cardiovascular: Drop in blood pressure due to dilatation of blood vessels. This can lead to lightheadedness and collapse. Cardiac arrest, a situation in which the heart stops can also happen in extreme cases and if the anaphylaxis is not treated promptly.
  • Gastrointestinal symptoms: Nausea, vomiting, Diarrhoea

What are the risk factors for developing anaphylaxis?

The risk of developing anaphylaxis is higher if you’ve had it before or if you are known to have allergies, eczema or asthma.

Other conditions that may increase the risk include heart disease and raised mastocytes (which are a type of white blood cell that increase in number with allergic reactions).


Anaphylaxis is a medical emergency and prompt treatment is required.

In the UK, if you suspect anaphylaxis you must follow the NHS advice, which is to call 999 for an ambulance and say that you think you’re having an anaphylactic reaction. If you can’t make the call, then you should ask someone else to call.

In terms of the medical treatment, once the ambulance arrives, they will administer intramuscular adrenaline from an EpiPen. This must be injected at the anterolateral aspect, the middle third of the thigh.

The Resuscitation Council UK has created the following guidelines that can be followed:


anaphylaxis guidelines

credit: Resuscitation Council UK

How can I prevent anaphylaxis?

The best way to prevent anaphylaxis is by avoiding allergens that you are known to be allergic to.

If you are known to have a strong allergy to a particular food (nuts for example), it is important to check the label before buying it. Food labeling laws in the UK enforce the need for businesses to tell customers whether the food they provide contains specific allergens. Although this requirement is limited to 14 of the allergens below, these are also the most common causes for food related anaphylaxis.

Cereals containing glutenGrainswheat, barley and oats
CrustaceansSeafoodprawns, crabs and lobsters
EggsAnimal products
MolluscsSeafoodfor example mussels and oysters
Sulphur dioxide and sulphitesChemicalsif the concentration is more than ten parts per million
Tree nutsNutsalmonds, hazelnuts, walnuts, brazil nuts, cashews, pecans, pistachios and macadamia nuts


Some of the ingredients below more often cause food intolerances rather than food allergies. This can also come in handy if you are known to be intolerant to one or more of the foods listed.

Allergy Testing

If you are unsure whether you are allergic to something or not, the best way to find out is to get an allergy test. The allergy testing techniques used in allergy clinics, such as skin prick tests or IgE blood testing are safe and effective at diagnosing allergies. Anaphylaxis can in very rare occasions happen during allergy testing too. For this reason, our skin prick tests are only conducted in the Nuffield Hospital clinic rooms. This is where clinical teams are available on-site in case of any emergencies. Furthermore, if the reactions you are describing do resemble anaphylactoid symptoms, we may first suggest an IgE blood test to the established allergen.

In conclusion, anaphylaxis is a critical medical emergency that requires immediate attention and it should not be ignored. If anaphylaxis is not treated straight away, the results can be deadly. It is usually treated by an initial shot of adrenaline/ EpiPen. Following this, the person should continue to be monitored and must go straight to A&E, in case the symptoms return.