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Jellyfish stings, from a UK beach graze to tropical envenomation.

Most UK stings are painful but manageable. A handful of tropical species are dangerous, and the first-aid ladder is not the same for every jellyfish.

Jump to first aid
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Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against UKHSA, Wilderness Medical Society and peer-reviewed marine envenomation sources.

  • 03

    Current for 2026

    Reflects up-to-date first-aid practice for UK species and specialist commissioned advice for tropical envenomation.

Key facts

Jellyfish stings at a glance.

The essentials, in plain English - the species that sting UK swimmers, the tropical species that can kill, and the first-aid principles that apply to both.

  • What it is

    Cnidarian envenomation - nematocysts discharge venom into skin on contact, causing local and, rarely, systemic effects.

  • UK species

    Mostly mild - moon jellyfish, lion’s mane and, increasingly with climate change, Portuguese man o’ war along southern and western coasts.

  • Travel species

    Box jellyfish (Chironex fleckeri) and Irukandji jellyfish in tropical waters are potentially fatal and need specialist commissioned tropical care.

  • First-aid basics

    Remove from water, rinse with seawater (not fresh), remove tentacles, and apply heat at 45°C for 20 minutes for most species.

  • Vinegar

    5% acetic acid inactivates undischarged nematocysts for tropical Australian jellyfish - not routinely used for common UK species.

  • When to worry

    Severe pain, autonomic surge, chest pain, breathing difficulty, collapse or extensive stings all need emergency assessment.

Why this guide matters

Species matters, and so does the first-aid ladder.

Vinegar, hot water, cold packs, adrenaline - each has a place, but not for every jellyfish. Getting the sequence right changes the outcome.

  • UK stings are usually manageable

    Moon jellyfish and most lion’s mane stings settle with simple first aid - seawater rinse, tentacle removal and hot water immersion.

  • Tropical envenomation is different

    Box jellyfish and Irukandji need vinegar, cardiac monitoring, IV magnesium, opioids and antivenom - specialist commissioned tropical care.

  • Never use fresh water

    Fresh water on undischarged nematocysts triggers them to fire and worsens envenomation - always seawater to rinse.

How the assessment is made

From the beach to a clear plan.

The steps a UK clinician or beach medic will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    Location and species

    Where and when - UK coast, Mediterranean or tropical waters - shapes the likely species and the risk profile.

  2. 02

    Assessing

    Envenomation site

    Look for linear, whip-like wheals, blisters, erythema and any tentacle fragments still stuck to the skin.

  3. 03

    Assessing

    Systemic review

    Vitals, pain score, breathing, chest pain, autonomic features and neurological signs - the flags for serious envenomation.

  4. 04

    Confirming

    Anaphylaxis screen

    Airway compromise, wheeze, urticaria beyond the sting or hypotension needs immediate adrenaline and hospital transfer.

  5. 05

    Confirming

    ECG and monitoring

    Suspected box jellyfish or Irukandji envenomation warrants cardiac monitoring for arrhythmia and catecholamine surge.

  6. 06

    Following up

    Tropical specialist input

    For confirmed or suspected tropical envenomation, arrange commissioned tropical medicine or emergency specialist review.

  7. 07

    Following up

    Wound review

    Follow-up at 48 to 72 hours for infection, blistering, delayed hypersensitivity and scar risk.

Typical timeline: on the beach in minutes, follow-up wound review in days.

Symptoms

What a jellyfish sting actually looks like.

The classic linear wheals and burning pain, the systemic features that mark severe envenomation, and the flags for anaphylaxis or cardiac involvement.

  • Linear wheals

    The classic whip-like, red, raised tracks that mark where a tentacle has brushed the skin.

  • Burning pain and erythema

    Immediate sharp or burning pain with surrounding redness - the most common presentation across species.

  • Blisters and vesicles

    Fluid-filled lesions appearing within hours - can progress in more potent stings like Portuguese man o’ war.

  • Necrosis in severe stings

    Skin breakdown along tentacle tracks in severe envenomation - warrants specialist wound review.

  • Delayed hypersensitivity

    Itchy, recurrent rash days to weeks later, sometimes at distant sites - a recognised late reaction.

  • Autonomic surge (Irukandji)

    Severe hypertension, tachycardia, sweating and impending doom - a catecholamine storm needing emergency care.

  • Cardiovascular collapse (box jellyfish)

    Rapid cardiotoxicity, arrhythmia and arrest within minutes - the deadliest jellyfish envenomation.

  • Red flag - anaphylaxis

    Breathing difficulty, throat swelling, widespread urticaria or hypotension needs adrenaline now.

First aid and treatment

How a jellyfish sting is managed.

Safety first, then a species-appropriate first-aid ladder - and specialist commissioned care for tropical envenomation, Irukandji and box jellyfish exposure.

  • Remove from water safely

    Get the person out of the sea, protect rescuers from further stings and lay them flat if unwell. Call 999 for severe envenomation.

  • Seawater rinse

    Rinse the sting area with seawater. Never use fresh water - it changes osmotic pressure and triggers residual nematocysts to fire.

  • Vinegar (5% acetic acid)

    Inactivates undischarged nematocysts of tropical Australian jellyfish including box jellyfish. Not first-line for common UK moon jellyfish.

  • Tentacle and nematocyst removal

    Remove visible tentacles with gloved hands or forceps, then lift residual nematocysts with shaving foam and a credit card edge.

  • Hot water immersion at 45°C

    Immerse the stung area in tolerably hot water for 20 minutes. Heat denatures many jellyfish venoms and relieves pain.

  • Cold packs if heat unavailable

    A reasonable second-line option for pain relief when hot water is not to hand - less effective at neutralising venom.

  • Topical and oral symptom relief

    Hydrocortisone cream, oral antihistamines and simple analgesia settle itch, wheal reaction and mild-to-moderate pain.

  • Specialist commissioned care

    Irukandji, box jellyfish and severe envenomation need emergency and commissioned tropical medicine input - IV magnesium, opioids and CSL antivenom where available.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and international marine envenomation standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP, A&E team or travel medicine clinician knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • UKHSA. Guidance on marine envenomation and travel health for UK residents.

  • Wilderness Medical Society. Clinical practice guidelines for the treatment of jellyfish stings.

  • NHS. Sting from sea creatures - self-help and when to seek care.

  • Australian Resuscitation Council. Guideline on envenomation - jellyfish stings.

Red flags

When a sting needs urgent attention.

Most UK stings settle in hours to days. These are the situations that don’t - and where emergency or specialist commissioned tropical care is needed.

  • Anaphylaxis

    Airway swelling, wheeze, hives beyond the sting site or hypotension needs intramuscular adrenaline and 999 - see our guide on drug and vaccine allergies.

  • Box jellyfish envenomation

    Extensive tentacle marks after swimming in tropical Australian waters - cardiac arrest can occur within minutes. Vinegar, CPR and CSL antivenom are life-saving.

  • Irukandji syndrome

    Severe hypertension, tachycardia, back and chest pain and a sense of impending doom 20 to 40 minutes after a tropical sting - a hospital emergency.

  • Chest pain or breathlessness

    Cardiotoxic venoms and stress can precipitate ischaemia or arrhythmia - low threshold for ECG, monitoring and admission.

  • Extensive body surface stings

    Large-area envenomation, particularly in children, risks systemic toxicity, rhabdomyolysis and compartment syndrome.

  • Rhabdomyolysis and dark urine

    Muscle breakdown after severe envenomation - IV fluids, monitoring of creatine kinase and renal function required.

  • Compartment syndrome

    Selective in severe limb envenomation - unremitting pain, pallor and tense swelling warrant urgent surgical review.

  • Delayed or worsening infection

    Spreading cellulitis, fever or lymphangitis in the days after a sting needs oral or intravenous antibiotics and tetanus review.

  • Sea anemone and fire coral confusion

    Fire coral and anemones cause similar burns and are often mistaken for jellyfish - the first-aid ladder is broadly the same.

Prevention

Simple habits, fewer stings.

Four practical things that cut the risk of a bad sting - protective clothing, situational awareness, a small first-aid kit and knowing your emergency threshold.

A quiet reminder

Prevention is dull, and it works.

Sting suits, beach flags and a small kit prevent far more trouble than any treatment can rescue.

  1. 01 Prevention

    Cover up in stinger waters

    Sting suits, rash vests and full wetsuits sharply cut the risk of tropical envenomation - non-negotiable in Chironex season.

  2. 02 Awareness

    Read the flags

    Follow lifeguard warnings on UK and Mediterranean beaches and heed stinger nets and beach closures in the tropics.

  3. 03 First aid

    Carry a small kit

    Vinegar, tweezers, gloves and a small heat source travel well - the difference between a bad afternoon and a hospital visit.

  4. 04 Escalate

    Know when to call 999

    Severe pain, breathing trouble, chest pain, collapse or extensive stings should always trigger emergency help.

Frequently asked

Everything we get asked about jellyfish stings.

Quick answers on UK species, tropical envenomation, vinegar, hot water and when to call 999.

  • What is a jellyfish sting?

    A jellyfish sting is cnidarian envenomation - specialised stinging cells (nematocysts) on tentacles fire microscopic barbs into the skin and inject venom. Most UK stings are painful but self-limiting; some tropical species cause severe systemic illness.

  • Which UK jellyfish should I worry about?

    Most UK stings are from moon jellyfish (mild) or lion’s mane (more painful, wheals and blistering). Portuguese man o’ war are showing up more often around southern and western UK coasts with warming seas - painful, occasionally severe stings that need medical attention.

  • Should I urinate on a jellyfish sting?

    No. Urine is not helpful and can make things worse. Rinse the sting with seawater (not fresh water), remove any tentacles carefully, and follow the hot water or vinegar step appropriate to the species involved.

  • When is vinegar the right treatment?

    Vinegar (5% acetic acid) inactivates undischarged nematocysts of tropical Australian jellyfish, including box jellyfish and Irukandji. For common UK moon jellyfish stings, hot water immersion at around 45°C for 20 minutes is generally the recommended approach.

  • When do I need to call 999?

    Call 999 for severe pain not controlled with simple measures, breathing difficulty, chest pain, collapse, confusion, extensive stings, stings to the face or genitals, or after any known or suspected box jellyfish or Irukandji exposure while travelling.

  • What is Irukandji syndrome?

    A delayed, severe reaction to tiny tropical jellyfish (Carukia barnesi and related species) 20 to 40 minutes after a barely-felt sting - severe hypertension, tachycardia, back and chest pain and a sense of impending doom. It needs emergency care with IV magnesium, opioids and commissioned tropical specialist input.

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