Anaphylaxis
Sources consulted
This article is original patient-education content.
- NICE—Anaphylaxis: assessment and referral after emergency treatment. CG134(2020)
- NHS—Anaphylaxis(2023)
- WHO—Anaphylaxis(2023)
- WAO—World Allergy Organization Anaphylaxis Guidelines(2020)
Based on international clinical guidelines
Overview
Anaphylaxis (say: an-a-fi-LAK-sis) is a severe, life-threatening allergic reaction that comes on very quickly — usually within minutes of contact with something the body sees as harmful. During anaphylaxis, the immune system (your body's defence system) overreacts dramatically, releasing a flood of chemicals that can send your body into shock. This means blood pressure can drop suddenly, airways can narrow, and the body's normal functions are thrown off balance all at once. It is a medical emergency that needs treatment right away.
Key facts
- Anaphylaxis is a severe allergic reaction that can be life-threatening and needs emergency treatment immediately.
- It can be triggered by foods, insect stings, medicines, latex, and other substances — sometimes with no obvious cause.
- Carrying an adrenaline auto-injector (a pre-filled pen that delivers emergency medicine) is the key safety step for people at risk.
Anaphylaxis is not everyday common, but it is not rare either. Studies suggest it affects roughly 1 in 300 people at some point in their lives. In the UK, hospital admissions for anaphylaxis have been rising over recent decades, though deaths remain relatively uncommon when treatment is given quickly.
Anaphylaxis can happen to anyone — any age, any background. Children and young people are more often affected by food-triggered reactions, while adults are more likely to be affected by insect stings or medicines. People who already have allergies or asthma have a higher chance of experiencing it, but a first reaction can occur in someone with no previous history.
Symptoms
- Swelling of the throat or tongue making it hard to breathe or swallow — call your local emergency number immediately
- Sudden severe difficulty breathing or wheezing that is getting worse — call your local emergency number immediately
- Collapse, loss of consciousness, or going limp — call your local emergency number immediately
- Rapid, very weak pulse combined with pale or blue skin — call your local emergency number immediately
- If an adrenaline auto-injector has been used, always call emergency services straight away, even if symptoms seem to improve — effects can wear off
- ⚠A mild allergic reaction (hives, itching, mild swelling) that is not yet severe but is spreading quickly — seek same-day care
- ⚠Any allergic symptoms in someone who has had a severe reaction before — seek same-day care even if currently mild
- ⚠Stomach pain, vomiting, or diarrhoea alongside skin symptoms after eating a known allergen — seek same-day care
Common symptoms
- Skin reactions — hives (itchy, raised, red or pale patches), flushing (skin going red and warm), or widespread itching
- Swelling of the face, lips, tongue, or throat
- Difficulty breathing, wheezing, or a tight feeling in the chest
- A sudden drop in blood pressure, causing dizziness or fainting
- Rapid or weak heartbeat (palpitations)
- Nausea, vomiting, stomach cramps, or diarrhoea
- Feeling of intense anxiety or a sense that something is very wrong
- Pale, clammy skin
- Loss of consciousness or collapse
Symptoms in children
- Sudden crying, distress, or unusual clinginess
- Drooling or difficulty swallowing
- A hoarse or strange-sounding cry or voice
- Going limp or floppy
- Skin that looks blotchy, pale, or blue-tinged around the lips
- Refusing food or drink, with sudden vomiting
- Clutching at the throat or chest
Symptoms in older adults
- Dizziness or sudden confusion, which may be mistaken for other conditions
- A greater risk of severe heart and circulation problems during a reaction
- Symptoms may progress more quickly and be harder to manage because of other existing health conditions
- Medicines taken for other conditions (such as beta-blockers for heart problems) may make a reaction harder to treat
Causes
Main causes
- Foods — especially peanuts, tree nuts (like cashews, walnuts, almonds), milk, eggs, fish, shellfish, wheat, and sesame
- Insect stings — most often from bees, wasps, and hornets
- Medicines — including antibiotics (infection-fighting medicines), non-steroidal anti-inflammatory drugs (pain relievers like ibuprofen-type medicines), and agents used in hospital procedures
- Latex — a type of rubber found in some gloves, balloons, and medical equipment
- Exercise — in some people, physical activity alone or in combination with a food or medicine can trigger a reaction
- Idiopathic anaphylaxis — a reaction with no identifiable cause, which can happen to some people
Risk factors
- Having a previous anaphylactic reaction — the most significant risk factor for future reactions
- Having asthma, especially if it is not well controlled
- Having other allergies, such as hay fever or eczema (a skin condition causing itching and redness)
- Being a child or young person (higher risk from food-related reactions)
- Taking certain medicines, such as beta-blockers or ACE inhibitors (both used for heart and blood pressure conditions), which can make reactions more severe or harder to treat
- Working in certain jobs — such as healthcare workers with frequent latex exposure, or beekeepers
When to see a doctor
See a doctor urgently if:
- After any suspected anaphylactic reaction, even if you felt better without treatment — a doctor must assess you the same day or as soon as possible
- If your current allergy medicines are not controlling your symptoms and reactions seem to be getting worse
- If you have been prescribed an adrenaline auto-injector but have never been properly shown how to use it
Book a routine appointment if:
- Schedule a follow-up appointment with an allergy specialist (a doctor who focuses on allergies and immune system problems) after any serious allergic reaction
- See your doctor to review your anaphylaxis action plan — a written guide explaining what to do if a reaction happens — at least once a year
- Talk to your doctor if you are finding it difficult to avoid your triggers in daily life
- Discuss your risk with a doctor before any planned surgery or procedure, especially if you have had drug reactions before
Diagnosis
There is no single test that confirms anaphylaxis on its own. Doctors diagnose it mainly by listening carefully to your description of what happened — what you were doing, what you ate or touched, how quickly symptoms came on, and exactly what symptoms you had. A detailed history is the most important tool. After a suspected reaction, you will usually be referred to an allergy specialist for further testing to identify what triggered the reaction.
Tests that may be done
- Blood tests — taken shortly after a reaction to measure a protein called tryptase (released by immune cells during a severe reaction), which can help confirm anaphylaxis happened
- Skin prick tests — a small amount of a suspected allergen (the substance causing the reaction) is placed on the skin; a small raised bump shows a possible allergy
- Specific IgE blood tests — these measure allergy antibodies (proteins the immune system makes against certain substances) in your blood to identify triggers
- Component testing — a more detailed blood test that looks at specific proteins within an allergen to better understand your level of risk
- Supervised challenge tests — sometimes done carefully in a hospital setting to confirm or rule out a specific food or medicine allergy, only when considered safe by a specialist
What to expect at your appointment
At your allergy appointment, expect a long and detailed conversation about your health history and the reaction you had. Tests are usually straightforward and not painful. The specialist will put all the results together to give you a clear picture of your triggers and risk, and will create a personal anaphylaxis action plan with you.
Treatment
Anaphylaxis is always treated as a medical emergency. The most important first treatment is an injection of adrenaline (also called epinephrine) — a natural hormone that quickly reverses the most dangerous effects of the reaction by opening airways, raising blood pressure, and calming the immune response. This is usually given into the outer thigh muscle. After an adrenaline injection, emergency services must always be called, and the person should lie down (with legs raised if dizzy, or sitting up if breathing is difficult). Hospital treatment follows to monitor and stabilise the person fully.
Self-care at home
- Always carry your prescribed adrenaline auto-injector (emergency pen) with you — never leave home without it, and carry two if advised
- Know exactly how and when to use your auto-injector, and make sure people close to you know too
- Wear a medical alert bracelet or carry a card explaining your allergy — this is very helpful if you cannot speak during a reaction
- Follow your written anaphylaxis action plan every time you suspect a reaction is starting
- Read food labels carefully every time you shop — ingredients can change without notice
- Tell restaurants, schools, workplaces, and airlines about your allergy in advance
- Check your auto-injector's expiry date regularly and replace it before it expires
- Avoid known triggers as carefully as possible in daily life
Medical treatments
In the emergency setting, adrenaline (epinephrine) given by injection is the cornerstone of treatment — it acts within minutes to reverse the most dangerous effects. In hospital, medical staff may also give oxygen to help with breathing, intravenous fluids (fluid given directly into a vein) to support blood pressure, and other medicines to reduce the immune reaction and ease breathing. A person is usually observed in hospital for several hours after treatment because a 'biphasic reaction' (a second wave of symptoms hours later) can sometimes occur. For long-term prevention, an allergy specialist may consider venom immunotherapy (a gradual desensitisation treatment — slowly introducing tiny amounts of an allergen, like bee venom, under medical supervision) for those with severe insect sting allergies. This approach can significantly reduce the risk of future reactions.
When is surgery considered?
Surgery is not a treatment for anaphylaxis. However, if you need any surgical or dental procedure and have a history of anaphylaxis — especially to medicines or latex — it is essential to inform your surgical team beforehand so they can take special precautions.
Living with this condition
Living with the risk of anaphylaxis takes preparation and awareness, but it does not have to stop you living life to the full. The foundation of day-to-day safety is always having your adrenaline auto-injector with you, knowing how to use it, and making sure the people around you — family, friends, teachers, colleagues — are aware of your allergy and what to do in an emergency. With good planning, most people with anaphylaxis risk manage their lives confidently.
Lifestyle tips
- Create and regularly review a written anaphylaxis action plan with your doctor — keep copies at home, at work, and at school if relevant
- Educate your close family, friends, and carers on how to recognise a reaction and how to use your auto-injector
- Tell your workplace, school, or university about your allergy so they can support you
- When eating out, always ask about ingredients — do not assume a dish is safe even if you have eaten it before
- Plan ahead for travel — carry enough auto-injectors, know how to access emergency care at your destination, and carry a translated allergy card if going abroad
- Register your auto-injector with the manufacturer so you can be notified of any recalls or shortages
- Keep a simple log of any reactions — even mild ones — to share with your allergy specialist
Diet and exercise
If your anaphylaxis is triggered by a food, working with a registered dietitian (a nutrition expert) can help you follow a safe, balanced diet while avoiding your trigger food. Avoiding a major food group can sometimes lead to nutritional gaps, so professional guidance is valuable. Exercise is generally healthy and encouraged — if exercise itself is a trigger for you (a rare condition called exercise-induced anaphylaxis), your allergy specialist will help you identify any patterns (for example, eating certain foods before exercise) and advise on safe ways to stay active.
Mental health and emotional wellbeing
It is completely understandable to feel anxious, frightened, or overwhelmed when living with the risk of a life-threatening reaction. Many people with anaphylaxis — and their families — experience worry, hypervigilance (being constantly on alert), or a reduced quality of life due to fear. If anxiety is affecting your daily life, relationships, or enjoyment of activities, please talk to your doctor. Psychological support, such as talking therapy, can make a real difference. You are not alone in feeling this way. If you are ever in emotional crisis, please reach out to a crisis support service in your area.
Prevention
You cannot always prevent a first reaction — sometimes it happens without warning. But after a reaction is identified, the main way to prevent future anaphylaxis is strict avoidance of your known trigger, careful planning, and always carrying your emergency adrenaline. For people with severe insect venom allergy, venom immunotherapy (a treatment that gradually reduces sensitivity to insect stings over time, given under medical supervision) can greatly reduce the risk of a future severe reaction. Wearing protective clothing outdoors and being cautious around insects also helps. For food allergy, reading labels, communicating with food providers, and never taking risks with unknown ingredients are key habits.
Vaccines
Some people have had allergic reactions to vaccines in the past. If this applies to you, always tell your healthcare provider before any vaccination. Vaccines are generally given in a clinical setting where staff are trained to manage allergic reactions, and the benefits of vaccination usually far outweigh the small risk. Your doctor can advise you on the safest approach for your situation.
Screening programmes
There is no routine population-wide screening for anaphylaxis risk. However, if you have had a severe allergic reaction, referral to an allergy specialist for thorough testing and risk assessment is strongly recommended. People with a family history of severe allergy may benefit from an allergy review, especially before introducing high-risk foods to young children — discuss this with your healthcare provider.
Complications
If left untreated
- Severe narrowing or complete blockage of the airway, making it impossible to breathe
- Dangerously low blood pressure (anaphylactic shock) leading to organ failure
- Loss of consciousness and, if untreated, brain damage from lack of oxygen
- Cardiac arrest (the heart stopping), which can be fatal
- A biphasic reaction — a second wave of severe symptoms hours after the first, even without further exposure to the trigger
Long-term outlook
With prompt treatment — especially quick use of adrenaline — the vast majority of people recover fully from an anaphylactic reaction with no lasting harm. Deaths from anaphylaxis are uncommon and are most often linked to delayed treatment. The outlook for people living with anaphylaxis risk is genuinely positive: with the right education, a clear action plan, and access to emergency medicine, most people lead full, active, and fulfilling lives. Regular follow-up with an allergy specialist helps keep your safety plan sharp and gives you the best possible protection.
Find support
International organisations
Local organisations
- Anaphylaxis Campaign ↗ · United Kingdom
- NHS — Anaphylaxis information ↗ · United Kingdom
- Allergy & Anaphylaxis Australia ↗ · Australia
- Food Allergy Canada ↗ · Canada
- Allergy & Asthma Network ↗ · United States
Helplines
External links open third-party websites. Ruqelo Health is not responsible for external content. Listing an organisation does not imply endorsement.
Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.