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Dr. Chrysoula I. Liakou MD, PhD
- Treated online: Assessment online. A doctor can go through a reaction afterwards, the likely trigger and your follow-up plan; anaphylaxis itself is treated with adrenaline and emergency care.
- What it is: a severe, life-threatening allergic reaction that affects the airway, breathing or circulation, usually starting suddenly after contact with a trigger.
- Common triggers: foods such as nuts, milk, eggs, fish and sesame, medicines such as antibiotics and anti-inflammatory painkillers, wasp and bee stings, and latex.
- After a reaction: carry 2 adrenaline auto-injectors at all times, and see an allergy specialist to confirm the trigger.
- Emergency: use an adrenaline auto-injector if you have one and call 112 for swelling of the throat or tongue, difficulty breathing, or feeling faint.
Do not book a video appointment if you or someone with you has swelling of the throat or tongue, difficulty breathing or swallowing, a hoarse voice, wheezing, or feels faint, confused or cold after contact with a possible trigger. Use an adrenaline auto-injector if there is one, call 112 and say “anaphylaxis”, and lie down with your legs raised.
Can an online doctor help with anaphylaxis?
Not during a reaction: anaphylaxis is treated with adrenaline and emergency care, so use an auto-injector if you have one and call 112. Where a doctor by video helps is afterwards and around the edges: going through what happened, narrowing down the likely trigger, checking you have and can use your adrenaline auto-injectors, arranging the referral to an allergy specialist, and assessing milder reactions such as hives or swollen lips without breathing problems.
How an online consultation helps after anaphylaxis
- The reaction gone through: What you ate, took or touched beforehand, how fast it started and what treatment you had, written down while it is fresh.
- A referral that happens: Anaphylaxis needs an allergy specialist to confirm the trigger, and the doctor makes sure the referral is in place.
- Your auto-injector plan: That you have 2 in date, know how to use them, and that the people around you know too.
- Your medicines reviewed: Some heart and blood pressure medicines can make a reaction harder to treat, so the doctor checks what you take.
What to do if someone has anaphylaxis
Use an adrenaline auto-injector straight away if there is one, call 112 and say “anaphylaxis”, and lie the person down with their legs raised. If they are no better after 5 minutes, use a second auto-injector. Do not let them stand or walk, even if they feel better.
- Use the auto-injector: inject into the outer thigh, following the instructions on the device. If in doubt, use it: it is also right when the symptoms seem mild but anaphylaxis is possible.
- Call 112: ask for an ambulance and say that you think it is anaphylaxis, even if the symptoms are improving.
- Lie down: lie flat with the legs raised. If breathing is difficult, raise the shoulders or sit up slowly. In pregnancy, lie on the left side.
- Remove a sting: if an insect stung, scrape the sting out of the skin if it is still there.
- Use a second auto-injector after 5 minutes: if there is no improvement, or the symptoms come back.
- Stay lying down: do not stand up or walk, even if you feel better. Standing up suddenly during anaphylaxis can be fatal.
- Go to hospital: everyone who has had anaphylaxis needs emergency care, even after the adrenaline has worked.
If the person stops breathing, start CPR and keep going until help arrives.
What the doctor checks in an online consultation after anaphylaxis
The doctor first makes sure the reaction is over and you are safe, then goes through it in detail. The doctor asks about:
- Now: whether you have any symptoms left, and whether anyone is with you.
- The reaction: what happened, how quickly it started, which symptoms you had and in what order, and how long it lasted.
- Possible triggers: food, drink, medicines, stings, latex, exercise, and anything new in the hours before.
- The treatment: whether adrenaline was used, how many doses, and how long you were kept in hospital.
- Your allergies: earlier reactions, known allergies, asthma and eczema.
- Your medicines: including heart and blood pressure medicines, and any anti-inflammatory painkillers.
- Your auto-injectors: whether you have 2, their expiry dates, and whether you and the people around you know how to use them.
Before the call, write down everything you ate, drank, took or touched in the hours before the reaction, and keep the discharge letter from the hospital to hand.
What is anaphylaxis?
Anaphylaxis is a serious, whole-body allergic reaction that usually starts suddenly and can be fatal without treatment. It happens when the immune system overreacts to something it has wrongly marked as dangerous, called an allergen, and releases chemicals that swell the airway, narrow the breathing tubes and drop the blood pressure. A tiny amount of the trigger can be enough.
What is anaphylactic shock?
Anaphylactic shock is anaphylaxis in which the blood pressure drops dangerously low, so not enough blood reaches the brain and organs. It causes faintness, confusion, cold, pale or clammy skin and collapse. Not every anaphylaxis leads to shock, but every anaphylaxis is an emergency.
How common is anaphylaxis?
Hospital admissions in England for allergy and anaphylaxis more than doubled in 20 years, from 12,361 in 2002 to 2003 to 25,721 in 2022 to 2023. With prompt treatment, most people make a full recovery.
What are the symptoms of anaphylaxis?
Swelling of the throat or tongue, difficulty breathing or swallowing, a hoarse voice, wheezing, feeling faint, dizzy or confused, and cold, pale, blue or grey skin or lips. There is often an itchy, raised rash too, but not always.
Swipe sideways to compare →
| What is affected | What you notice |
|---|---|
| Airway | Swelling of the throat or tongue, difficulty swallowing, tightness in the throat, a hoarse voice |
| Breathing | Breathing very fast or with difficulty, wheezing, coughing, noisy breathing |
| Circulation | Feeling faint or dizzy, fainting, feeling tired or confused, skin that is cold to the touch, blue, grey or pale skin, lips or tongue |
| Skin | Often an itchy, raised or swollen rash, flushing, or swelling of the lips, eyelids or face |
Any problem with the airway, breathing or circulation after contact with a possible trigger means anaphylaxis, and needs adrenaline and an emergency call.
How quickly does anaphylaxis start?
Usually fast, in the first few minutes after contact with the trigger, and it gets worse quickly. Reactions can occasionally start up to 2 to 3 hours later. In fatal reactions, collapse after a sting typically came within a quarter of an hour, breathing stopped after about 30 minutes with food, and reactions to a medicine given into a vein were quickest of all.
Anaphylaxis without a rash
Skin changes are missing or easy to miss in up to 1 in 5 reactions, so a person can have anaphylaxis with no rash at all. Breathing or circulation problems after a possible trigger are enough on their own. A rash on its own, without any of them, is not anaphylaxis.
Anaphylaxis or a milder allergic reaction?
Most allergic reactions are mild to moderate: an itchy rash, hives, sneezing, itchy eyes, or swelling of the lips, eyes or face, with normal breathing and no faintness. They usually settle with an antihistamine. What makes a reaction anaphylaxis is a problem with the airway, breathing or circulation.
Swipe sideways to compare →
| Sign | Milder allergic reaction | Anaphylaxis |
|---|---|---|
| Skin | Itchy rash, hives, flushing | May have the same, or no rash at all |
| Swelling | Lips, eyelids or face | Throat or tongue, with difficulty swallowing or a hoarse voice |
| Breathing | Normal | Wheezing, noisy, fast or difficult breathing |
| Circulation | Normal | Faint, dizzy, confused, pale, cold or clammy, collapse |
| What to do | Antihistamine, and see a doctor | Adrenaline auto-injector, and call 112 |
A milder reaction is still worth checking with a doctor, because knowing the trigger matters for next time. See allergic reaction, hives and angioedema.
What causes anaphylaxis?
Anaphylaxis is triggered by something the person is allergic to. The common triggers are:
- Foods: nuts, cows’ milk, eggs, fish and sesame. See food allergy and nut allergy.
- Medicines: antibiotics, anti-inflammatory painkillers such as ibuprofen, and medicines used in anaesthesia. See penicillin and drug allergy.
- Insect stings: wasps and bees. See wasp stings and bee stings.
- Latex: the rubber in some gloves and condoms.
In the UK, food accounts for about 35% of hospital admissions coded as anaphylaxis, medicines about 17% and insect stings about 6.5%. Medicines cause more of the deaths: 39%, against 19% for food and 14% for stings. Food is the most common trigger in young people, and fatal reactions to medicines are most common in older adults. Sometimes no trigger is ever found.
Who is most at risk of a severe reaction?
- people with asthma, especially when it is poorly controlled, and people who have had a severe reaction before
- older adults with heart disease who take several medicines
- people who take beta blockers, which can make adrenaline work less well
- anyone whose adrenaline is delayed
Can a food intolerance cause anaphylaxis?
No. A food intolerance, such as lactose intolerance, does not involve the immune system, and anaphylaxis is an immune reaction. A true food allergy can cause anaphylaxis.
How is anaphylaxis treated?
Adrenaline is the treatment for anaphylaxis, given into the muscle of the outer thigh and repeated every 5 minutes if needed. In hospital, adrenaline may also be given by drip into a vein, with oxygen and fluids. Besides auto-injectors, adrenaline now also comes as a nasal spray for some people with a severe allergy.
Do antihistamines treat anaphylaxis?
No. Antihistamine tablets do not treat the breathing and circulation problems of anaphylaxis, and taking one must never delay adrenaline. Once the person is stable, a non-drowsy antihistamine can ease an itchy rash. Steroids are no longer given routinely, and never instead of adrenaline.
How long do you stay in hospital after anaphylaxis?
Usually between 2 and 12 hours, sometimes longer, because symptoms can come back. How long depends on how the reaction went:
Swipe sideways to compare →
| How the reaction went | Usual observation after the symptoms have gone |
|---|---|
| Quick, complete response to one dose of adrenaline given early, unused auto-injectors at home, training, and someone with you afterwards | At least 2 hours |
| Two doses of adrenaline needed, or a biphasic reaction in the past | At least 6 hours |
| A severe reaction needing more than two doses, severe asthma or breathing problems, a medicine still being absorbed, arriving late at night, or living far from emergency care | At least 12 hours |
Blood tests after anaphylaxis
Adults usually have blood taken for a test called mast cell tryptase: the first sample as soon as possible after treatment starts, and a second ideally within 1 to 2 hours, and no later than 4 hours, from the start of the symptoms. A raised level helps the allergy specialist confirm that it was anaphylaxis.
Before you leave hospital
- You should be given 2 adrenaline auto-injectors, or a prescription for them, and shown how to use them.
- You should be told about the signs of anaphylaxis, the risk of a second reaction, and what to do if it happens again.
- You should be referred to an allergy specialist, and told how to avoid the suspected trigger.
What is a biphasic reaction?
A biphasic reaction is a second wave of anaphylaxis that starts hours after the first has settled, without any new contact with the trigger. It happens in around 5% of people, and the median time before it starts is around 12 hours. This is why people are kept in hospital after anaphylaxis, why someone should be with you after you go home, and why the auto-injectors stay within reach.
If symptoms come back, treat them exactly like the first reaction: use an auto-injector and call 112.
What might the doctor recommend after a severe allergic reaction?
What happens next depends on what happened, how it was treated and what is still unclear. This is the framework the doctors use:
Swipe sideways to compare →
| What you have | Likely first step | Suitable for online care? | When in-person care is needed |
|---|---|---|---|
| Swelling of the throat or tongue, breathing difficulty, or feeling faint | Adrenaline auto-injector and emergency treatment | No | Call 112 now |
| Treated for anaphylaxis in hospital, now at home | A follow-up plan: trigger, auto-injectors and referral | Yes | For allergy tests at a specialist clinic |
| Hives, or swollen lips or eyelids, with normal breathing | Antihistamine and an assessment of the trigger | Yes | If breathing, swallowing or the voice changes: call 112 |
| A reaction to a medicine | Recording the allergy, and safe alternatives | Partly | Allergy testing to confirm or remove the label |
| Auto-injectors used, lost or out of date | Advice on replacing them and on your action plan | Yes, to assess | Replacements are prescribed after a review of your allergy |
| Anaphylaxis with no known trigger | Referral to an allergy specialist | Partly | For tests at an allergy clinic |
Had a severe allergic reaction? A doctor can go through what happened and the follow-up you need in one consultation.
See available times →Living with a risk of anaphylaxis
- Carry 2 adrenaline auto-injectors with you at all times, because a second dose may be needed.
- Use one if you think you may have anaphylaxis, even if the symptoms are mild.
- Check the expiry dates regularly and replace them before they run out. Do not store them anywhere too hot or cold, such as the fridge or in the sun.
- Practise with a trainer device, and show family, friends, colleagues or carers how and when to use yours.
- Avoid your trigger: read food labels every time, and tell restaurant and café staff about your allergy.
- Wear medical alert jewellery, such as a bracelet that names your allergy.
- Keep your asthma well controlled, if you have it.
Getting the trigger confirmed
An allergy specialist uses your account of the reaction, skin prick or blood tests, and sometimes a supervised challenge, to confirm what caused it and what is safe. See allergy testing.
Special situations
Pregnancy
Anaphylaxis is treated with adrenaline in pregnancy too. Lie on your left side rather than flat on your back, and call 112.
Asthma
Asthma, especially poorly controlled asthma, raises the risk of a severe reaction. Wheezing after contact with a trigger is a breathing problem, so it counts as anaphylaxis: use the auto-injector. If in doubt, use it. See asthma.
A strange reaction to red meat
Hives or anaphylaxis 2 to 6 hours after eating beef, pork or lamb can be alpha-gal syndrome, a meat allergy linked to tick bites. See alpha-gal syndrome.
Travelling in Europe
Keep both auto-injectors with you, check their expiry dates before you go, and carry a written note of your allergy. 112 is the emergency number across the European Union.
Children
Mobi Doctor consultations are for adults aged 18 and over. A child who is unwell needs a paediatrician or a local doctor in person, and emergency signs in a child mean 112.
When anaphylaxis is assessed online, and when you need in-person care
Assessed online: the follow-up after a reaction, the likely trigger, your auto-injector plan, the referral to an allergy specialist, and milder allergic reactions without breathing or circulation problems.
In-person care: every anaphylaxis, which needs adrenaline and emergency care, the observation in hospital, and the allergy tests that confirm the trigger.
When to get in-person care
Use an adrenaline auto-injector if you have one, and call 112 now for:
- swelling of the throat or tongue, difficulty swallowing, or a hoarse voice
- difficulty breathing, breathing very fast, wheezing or noisy breathing
- feeling faint, dizzy, tired or confused, or collapsing
- skin that is cold to the touch, or blue, grey or pale skin, lips or tongue
- symptoms coming back after a reaction, or after an auto-injector has been used
Get medical advice the same day for:
- an itchy rash, hives or swelling of the lips or eyelids after a food, medicine or sting, with normal breathing
- a reaction after which you have no auto-injectors left
- a first reaction to a medicine you still need to take
How Mobi Doctor works
- Book a time that suits you: daily 7am–11pm CEST. You can see a doctor over video, usually within 15 minutes. No subscription, and the exact price is shown before you pay.
- Speak to a licensed doctor about the reaction: say what happened, what you ate, took or touched beforehand, how quickly it started and what treatment you had.
- Leave with a plan: what to avoid, what to carry, who you are referred to, and which signs mean you should be seen in person. If the doctor prescribes, use the prescription at a pharmacy near you.
No sign-up needed
If you have any warning sign listed on this page, call 112 now. Otherwise, tick every symptom you have to see each condition page that mentions it. It finds the right page, not a diagnosis: a doctor gives you that on a video call.
Tap the body — an area or a point — to browse symptoms anywhere
Similar symptoms, different condition? Allergic Reaction can start the same way. Compare them, or look up any other symptom in the full symptom checker.
Frequently asked questions about anaphylaxis
What is anaphylaxis?
Anaphylaxis is a serious, whole-body allergic reaction that usually starts suddenly and can be fatal without treatment. It affects the airway, breathing or circulation, and is treated with adrenaline.
What are the first signs of anaphylaxis?
The first signs of anaphylaxis are swelling of the throat or tongue, difficulty breathing or swallowing, a hoarse voice, wheezing, feeling faint or confused, and cold, pale or blue skin. An itchy, raised rash often comes too, but not always.
What should you do if someone has anaphylaxis?
Use their adrenaline auto-injector in the outer thigh, call 112 and say anaphylaxis, and lie them down with their legs raised. Use a second auto-injector if they are no better after 5 minutes, and do not let them stand up.
How quickly does anaphylaxis happen?
Anaphylaxis usually starts in the first few minutes after contact with the trigger, and it gets worse quickly. Occasionally it starts up to 2 to 3 hours later.
What is the difference between anaphylaxis and anaphylactic shock?
Anaphylactic shock is anaphylaxis in which the blood pressure drops dangerously low, so the person feels faint, confused or very drowsy, looks pale or grey and may collapse. Anaphylaxis can also affect mainly the airway and breathing without shock, and both are emergencies treated the same way: adrenaline into the outer thigh, lying flat with the legs raised, and a 112 call.
Can you survive anaphylactic shock?
Yes. With prompt adrenaline and emergency treatment, most people make a full recovery. Delay is what makes anaphylaxis dangerous, so use an auto-injector straight away.
How long does it take to recover from anaphylaxis?
After anaphylaxis, most people are observed in hospital for 2 to 12 hours, longer after a severe reaction, and feel back to normal soon afterwards. You then need a follow-up plan and a referral to an allergy specialist.
What is a biphasic reaction?
A second wave of anaphylaxis hours after the first has settled, without new contact with the trigger. It happens in around 5% of people, typically around 12 hours later.
Can anaphylaxis happen in your sleep?
A second, biphasic wave of anaphylaxis can start hours later, including at night. That is why someone should be with you after you go home from hospital, and why auto-injectors should stay within reach.
Do antihistamines stop anaphylaxis?
No. Antihistamines do not treat the breathing and circulation problems of anaphylaxis and must never delay adrenaline. They can ease an itchy rash once the person is stable.
How can anaphylaxis be prevented?
Know your trigger and avoid it strictly: read every label, ask about ingredients when eating out, tell friends and colleagues, and treat cross-contamination seriously; carry 2 adrenaline auto-injectors everywhere and check their dates, make sure the people around you know how to use them, and wear medical alert jewellery. Keep asthma well controlled, because poorly controlled asthma makes anaphylaxis more dangerous, and see an allergy specialist, who can confirm the trigger, update your plan and, for stings, offer immunotherapy that prevents further anaphylaxis.
Why do you need two adrenaline auto-injectors?
One dose of adrenaline is not always enough to stop anaphylaxis. If there is no improvement after 5 minutes, or the symptoms come back, the second one is used while you wait for the ambulance.
Can an online doctor help after anaphylaxis?
Yes, with the follow-up: going through the reaction and the likely trigger, checking your auto-injectors, and arranging a referral to an allergy specialist. Anaphylaxis itself needs adrenaline and emergency care.
- Anaphylaxis, NHS, National Health Service (UK), reviewed 21 June 2023.
- Emergency treatment of anaphylaxis, Resuscitation Council UK, guideline, May 2021.
- Anaphylaxis: assessment and referral after emergency treatment (NG258), NICE, National Institute for Health and Care Excellence, published 27 May 2026.
- MHRA reinforces anaphylaxis emergency guidance as hospital admissions rise, MHRA, Medicines and Healthcare products Regulatory Agency (UK), 2 August 2023.
- Anaphylaxis, Cleveland Clinic (US), updated 17 October 2023.
- About anaphylaxis, Anaphylaxis UK, part of Allergy UK, accessed 15 October 2026.
- Food allergy, NHS, National Health Service (UK), reviewed 20 August 2026.
- Allergies, NHS, National Health Service (UK), reviewed 5 March 2026.
- Food allergy and food intolerance, BDA, British Dietetic Association, food fact sheet, reviewed March 2024.
- Alpha-gal syndrome, UKHSA, UK Health Security Agency, updated 12 January 2026.
This page is for information only and is not a substitute for a medical consultation. Guideline links are provided for transparency; treatment decisions are made with your doctor.
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