Anaphylaxis: symptoms, what to do and treatment

The NHS says symptoms of anaphylaxis happen very quickly, usually starting within minutes of coming into contact with something you are allergic to, such as a food, medicine or insect sting. NHS inform says it usually develops within the first few hours of contact with an allergen, but it can sometimes happen later.

You may also have a rash that is swollen, raised or itchy. NHS inform says that skin rash, swelling of the face, lips or eyes and stomach symptoms such as abdominal pain, nausea or vomiting are unlikely to be a sign of anaphylaxis on their own.

• Swelling of the throat and tongue.

• Difficulty breathing or breathing very fast; wheezing, coughing or noisy breathing.

• Difficulty swallowing, tightness in the throat or a hoarse voice.

• Feeling tired or confused; feeling faint, dizzy or fainting.

• Skin that feels cold to the touch.

• Blue, grey or pale skin, lips or tongue (on brown or black skin this may be easier to see on the palms of the hands or soles of the feet).

• In a child: being limp, floppy or not responding like they normally do.

The NHS says anaphylaxis happens when your body has a serious reaction to something you are allergic to. NHS inform explains that it is caused by a problem with the immune system: the immune system overreacts to a harmless substance and releases chemicals such as histamine.

NHS inform says people of any age can be affected, but it is not common. You may be at more risk if you have another condition such as asthma or eczema. Anaphylaxis is also called anaphylactic shock.

The NHS lists the steps to follow if you think you or someone you are with is having an anaphylactic reaction.

• Use an adrenaline auto-injector (such as an EpiPen) if you have one. Instructions are on the side of the injector.

• Call 999 for an ambulance and say that you think you are having an anaphylactic reaction.

• Lie down. You can raise your legs, and if you are struggling to breathe, raise your shoulders or sit up slowly. If you are pregnant, lie on your left side.

• If you have been stung by an insect, try to remove the sting if it is still in the skin.

• If your symptoms have not improved after 5 minutes, use a second adrenaline auto-injector.

• Do not stand or walk at any time, even if you feel better.

The NHS says to call 999 if any of the following happen. These can be signs of a serious allergic reaction and may need immediate treatment in hospital. NHS inform says to phone 999 if you or someone else has signs of anaphylaxis.

• Your lips, mouth, throat or tongue suddenly become swollen.

• You are breathing very fast or struggling to breathe (you may become very wheezy or feel like you are choking or gasping for air).

• Your throat feels tight or you are struggling to swallow.

• Your skin, tongue or lips turn blue, grey or pale.

• You suddenly become very confused, drowsy or dizzy.

• Someone faints and cannot be woken up.

• A child is limp, floppy or not responding like they normally do.

The NHS says anaphylaxis needs to be treated in hospital immediately. Treatments can include adrenaline given by an injection or drip into a vein, oxygen, and fluids given by a drip. You will usually stay in hospital for around 2 to 12 hours, but may need to stay longer.

NHS inform says you need to go to hospital after anaphylaxis, even if you have been given adrenaline, because symptoms can sometimes come back. You will usually be observed for 6 to 12 hours, and other treatments may include antihistamines and corticosteroids. You may need to take other medicines for 2 to 3 days after leaving hospital to help stop symptoms returning, and you will usually be asked to attend a follow-up appointment.

NHS inform explains that adrenaline narrows blood vessels, which raises blood pressure and reduces swelling, and opens the airways, which can relieve breathing difficulties.

The NHS says that before you leave hospital you should be given 2 adrenaline auto-injectors, or a prescription for them, and be shown how to use them each time you are prescribed them. The Resuscitation Council UK quotes MHRA advice that 2 adrenaline auto-injectors should be prescribed and carried at all times, that people with allergies and their carers should be trained to use the particular device they have been prescribed, and that they should practise with a trainer device.

There are different types. NHS inform names EpiPen, Jext and Emerade, and says each type is slightly different, so read the instructions carefully. The NHS and NHS inform give the following practical points.

• Carry 2 adrenaline auto-injectors with you at all times.

• Check the expiry dates regularly and get new ones before they expire; an out-of-date injector offers limited protection.

• Do not leave them anywhere too hot or cold, such as the fridge or in the sun.

• Practise using a trainer injector, and teach friends, family, colleagues or carers how and when to use yours.

• Use your auto-injector if you think you may have anaphylaxis, even if symptoms are mild. Do not delay.

• Wear medical alert jewellery or carry an emergency card with details of your allergy.

The NHS says allergies that can sometimes cause anaphylaxis include foods such as nuts, cows' milk, eggs, fish or sesame seeds, medicines such as antibiotics or non-steroidal anti-inflammatory drugs (NSAIDs), insect stings such as wasp and bee stings, anaesthetics and latex. NHS inform adds fruit, shellfish, and contrast agents used for scans.

Sometimes it is not known what caused an anaphylactic reaction. If you have had anaphylaxis, NHS inform says you may be referred to an allergy clinic for tests to find out more about your triggers, and the NHS says you may be referred to an allergy specialist for tests and advice.

The sources do not give a single duration, because treatment stops the reaction. The NHS says symptoms start within minutes, hospital stays are usually around 2 to 12 hours, and NHS inform says you will usually be observed for 6 to 12 hours. NHS inform explains that symptoms can sometimes return, called a biphasic reaction, which is why observation and follow-up are needed.

The NHS and NHS inform give general advice for people who have had anaphylaxis or are at risk.

• Avoid the food, medicine or other trigger you are allergic to.

• Check food labels carefully, tell staff at restaurants and cafes, and tell airlines and cabin staff before you fly. Remember that some foods may contain small traces of allergens.

• Always tell healthcare professionals about any medicine allergies; there may be an alternative.

• For insect stings, move away slowly without swatting, and use repellent outdoors. NHS inform says some specialist allergy clinics offer desensitisation.

• Attend the allergy clinic follow-up if you are referred.

Anaphylaxis is always an emergency, and care starts with 999 and the emergency department. Follow-up on the NHS is usually through an allergy clinic, where tests can identify triggers and you are given advice and a plan, as NHS inform describes.

Some people choose to see a private allergy specialist for tests or a second opinion after a reaction. In general terms the same steps apply: confirm the diagnosis, identify possible causes, advise on avoidance and emergency management, and train you to use your auto-injector. Make sure your GP knows the outcome so that auto-injector prescriptions and reminders are kept up to date.