Anaphylaxis and Severe Reactions

If you are experiencing a serious reaction or anaphylaxis, call 999 immediately.

Anaphylaxis is a life threatening severe allergic reaction. It is a medical emergency and requires immediate treatment. A severe allergic reaction can cause an anaphylactic shock and must be treated with adrenaline.

Jump to…

• Common triggers
• Signs and symptoms
• Treating anaphylaxis
• What happens after an anaphylactic reaction?
• Getting a diagnosis
• What can make an allergic reaction more serious?

What happens during anaphylaxis?

In most allergic reactions the resulting chemicals are released locally into the tissues in a particular part of the body (skin, eyes etc.). This means the symptoms of the allergic reaction usually only occur in this area.

In anaphylaxis, the chemicals that cause the allergic symptoms (e.g. histamine) are released into the bloodstream. The symptoms of anaphylaxis usually occur within minutes of exposure to the trigger substance (allergen) but sometimes an hour or so later.

Factsheet: Anaphylaxis and Severe Allergic Reactions

Common triggers of anaphylaxis

The most common causes of anaphylactic reactions include:

• Foods: including nuts, milk, fish, shellfish, eggs and some fruits
• Medicines and drugs: including some antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin
• Insect stings: particularly wasp and bee stings
• General anaesthetic
• Contrast agents: dyes used in some medical tests to help certain areas of your body show up better on scans
• Latex: a type of rubber found in some rubber gloves and condoms.

In some cases, there’s no obvious trigger. This is known as idiopathic anaphylaxis.

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Signs and symptoms of anaphylaxis

An allergic reaction is considered to be anaphylaxis when it involves difficulty in breathing or affects the heart rhythm or blood pressure. In extreme cases there could be a dramatic fall in blood pressure. The person may become weak and floppy and may have a sense of something terrible happening.
Any one or more of the following symptoms may be present, these are often referred to as the ABC symptoms.

• Airway: swelling in the throat, tongue or upper airways, hoarse voice, difficulty swallowing.
• Breathing: Sudden onset wheezing, breathing difficulty, noisy breathing, persistent cough.
• Circulation: Dizziness, feeling faint, sudden sleepiness, confusion, pale clammy skin, loss of consciousness or collapse.

Any of the ABC symptoms may lead to collapse and unconsciousness and, on rare occasions, can be fatal.

Knowing how to recognise the symptoms of anaphylaxis can provide individuals and their caregivers with peace of mind, empowering them to navigate their allergy management confidently.

Anaphylaxis can occur rapidly and escalate quickly, making it essential to recognise the signs and symptoms early on.

Additional Symptoms

Mild to moderate symptoms may include:

• A red raised itchy rash (known as hives or urticaria) anywhere on the body
• Swelling of the face, lips and/or eyes
• A tingling or itchy feeling in the mouth
• Mild throat tightness
• Stomach pain, vomiting or diarrhoea.

These symptoms can also happen on their own. If you don’t have the ABC symptoms, the reaction is likely to be less serious and is not the same as anaphylaxis but watch carefully in case ABC symptoms develop.

To be prepared and to help you and those around you know what to do in an emergency, it’s important to have an allergy action plan.

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Treating anaphylaxis

If you have mild allergic symptoms, you may be prescribed antihistamine medicine that you take by mouth. But if you are at risk of a serious allergic reaction (anaphylaxis), you may be prescribed adrenaline, the emergency medicine used to treat anaphylaxis.

Anaphylaxis can develop quickly, so having access to adrenaline that can be given promptly is an important part of being prepared. Adrenaline devices are available in different forms and are designed to be straightforward to use in an emergency.

Options currently available on prescription in the UK include:

• Adrenaline auto-injectors (AAIs) – such as EpiPen and Jext
• Intranasal adrenaline – EURneffy, a needle-free nasal spray.

If you have been prescribed an adrenaline device, it’s important to know when and how to use it. A healthcare professional can show you how to use your specific device, and you can also find guidance, training materials and practice devices through the manufacturer websites.

You must carry two in-date forms of prescribed adrenaline at all times as a second dose may be needed if symptoms do not improve after five minutes or get worse.

Find out more about adrenaline devices

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What happens after an anaphylactic reaction

After having an anaphylactic reaction, you will need to go to hospital for observation, usually for 6-12 hours, as the symptoms can occasionally return during this period.

While in hospital:

• An oxygen mask may be used to help breathing
• Fluids may be given directly into a vein to help increase blood pressure
• Additional medicines such as antihistamines and steroids may be used to help relieve symptoms
• Blood tests may be carried out to confirm anaphylaxis

You should be able to go home when the symptoms are under control and it’s thought they will not return quickly. This will usually be after a few hours, but may be longer if the reaction was severe.

You may be asked to take antihistamines and steroid tablets for a few days after leaving hospital to help stop your symptoms returning.

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Getting a diagnosis

Getting the right diagnosis, information and treatment is an important first step in managing a allergies and anaphylaxis. Understanding what your triggers are can help you reduce your risk of reactions and feel more confident managing your allergy day to day.

Seeing your GP or healthcare professional

If you think you may have an allergy, speak to your GP or another healthcare professional. This is particularly important if you have experienced anaphylaxis.

When you first seek help for a suspected allergy, you should be assessed by a healthcare professional with appropriate knowledge of allergy. They should be able to advise whether you need further assessment and, where appropriate, refer you to an allergy service.

If your allergy is serious or potentially life-threatening, you should receive an urgent referral to a healthcare professional with the appropriate expertise.

You can ask to be referred to a specialist-led allergy clinic if you feel this is appropriate, even if the clinic is outside your immediate local area.

Children with suspected or confirmed allergy should be assessed by a healthcare professional with appropriate expertise in paediatric allergy. Depending on their needs, this may include a consultant paediatric allergist.

People who require specialist care should have access to a comprehensive allergy service with a dedicated allergy team.

Referral to an allergy clinic

Your GP may refer you to an allergy clinic for further assessment and testing. Allergy services vary across the UK, so your GP can advise on the most appropriate local service.

Allergy UK’s helpline can help you find your nearest NHS or private allergy testing clinics around the UK.

Contact our Helpline team

Seeing an allergy specialist

Some allergies can be diagnosed and managed in primary care, while others require specialist assessment. You may benefit from seeing an allergy specialist if:

• Your allergy symptoms significantly affect your daily life
• You have experienced a severe or potentially life-threatening reaction
• You have complex or multiple allergies
• Your diagnosis is unclear or requires further investigation

During an allergy assessment, the specialist will consider your medical history, symptoms and previous reactions to help identify possible triggers. They may recommend targeted tests, such as skin prick or blood tests, and in some circumstances a supervised food or allergen challenge.

Factsheet: Testing and Diagnosing Food Allergies
Factsheet: Oral Food Challenge

Your allergy care plan

Following your assessment, you should receive a care plan that is tailored to your individual needs. This may include:

• Information about your allergy and potential triggers
• Advice on avoiding known allergens and reducing your risk of a reaction
• Medication and guidance on how to use it
• Advice about whether you need prescribed adrenaline
• Clear instructions about what to do if you have an allergic reaction
• Advice for managing your allergy in everyday situations

You should have enough time during your appointment to discuss your symptoms, treatment options and any concerns you have, so that you understand and feel comfortable with your care plan.

If you feel your current care is not meeting your needs, you can ask your healthcare professional about seeking a second opinion.

Care after a serious allergic reaction

If you have experienced anaphylaxis or another serious allergic reaction, you should receive appropriate follow-up care and be referred to an allergy specialist for further assessment, even if you have previously seen an allergy specialist.

The assessment should aim to identify the likely cause or trigger of the reaction and help you understand how to reduce the risk of another reaction. Your ongoing treatment and emergency medication should also be reviewed.

If you are considered to be at risk of serious allergic reactions, you should have access to appropriate ongoing specialist care.

Depending on your allergy and individual circumstances, this may include specialist investigations, regular reviews, advice on allergen avoidance and, where appropriate, treatments such as allergen-specific immunotherapy.

Your healthcare needs may change over time, so speak to your GP, allergy specialist or other healthcare professional if your symptoms change or your treatment is no longer meeting your needs.

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Allergy action plans

A written allergy action plan can help you and the people around you recognise the signs of an allergic reaction and understand what to do in an emergency. Your plan should be personalised to your allergy and include clear information about your symptoms, medication and the steps to take if you have a reaction.

Your allergy clinic or GP can help you create or update an allergy action plan. Our Helpline team can also provide information and support.

Find out more about allergy action plans

What can make an allergic reaction more serious?

There may be times when you are more vulnerable to having a serious allergic reaction. Certain circumstances can increase the risk or severity of a reaction, so it is particularly important to take care to avoid your known allergens during these times.

You may be at increased risk of a more serious reaction:

• If you have asthma that is poorly controlled
• If you exercise just before or just after contact with the allergen
• During times of emotional stress
• If you have taken a ‘non-steroid anti-inflammatory drug’ (NSAID) such as aspirin or ibuprofen
• If you are suffering from an infection, or have recently had one
• If you are also suffering from hay fever
• If you have been drinking alcohol

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