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Jellyfish stings: which ones matter and how to treat them

Most jellyfish stings are painful and forgettable. A small number of species are genuinely dangerous, and they are concentrated in tropical Indo-Pacific waters — box jellyfish off northern Australia and Southeast Asia, and Irukandji further offshore. Knowing which water you are in decides whether a sting is an inconvenience or an emergency.

  • 8High risk
  • 31Medium
  • 2Low
  • 41Zones tracked

The species that matter

Box jellyfish (Chironex fleckeri) off northern Australia, Thailand, Malaysia and the Philippines can kill within minutes; they are near-invisible in the water. Irukandji are thumbnail-sized and cause a delayed, severe systemic syndrome 20–40 minutes after a mild sting. The Portuguese man o' war — not a true jellyfish — delivers a long, intensely painful sting across the Atlantic, the Canaries and the Mediterranean. Everything else is usually a local sting.

Vinegar is not universal

Vinegar is the correct first response to a tropical box jellyfish sting — it stops undischarged stinging cells firing. It is the wrong response to a Portuguese man o' war, where it may make things worse. If you do not know what stung you and you are outside box jellyfish waters, rinse with seawater and use hot water instead.

How to avoid it

  • Obey purple or jellyfish-warning flags, and swim inside stinger nets where they are provided.
  • In northern Australia during the wet season, wear a full stinger suit rather than relying on avoidance.
  • Never touch a jellyfish washed up on the beach — beached specimens still sting, sometimes for days.
  • Note where the vinegar stations are on tropical beaches before you swim.

If it happens

  • Box jellyfish waters: douse with vinegar for at least 30 seconds, call emergency services immediately, and be ready to start CPR.
  • Elsewhere: rinse with seawater — not fresh water, which fires more stinging cells — and lift off remaining tentacles with a gloved hand or a card edge.
  • Immerse the area in hot water at about 45°C for 20–45 minutes for pain relief.
  • Get urgent help for any sting causing breathing difficulty, chest or back pain, cramps, vomiting or a sense of doom — this is the Irukandji pattern and it appears well after the sting.

General guidance only — not a substitute for medical advice or local emergency services.

Where we track it

41 zones in the Dangers Here hazard database, by danger level.

High

  • Broome & Kimberley Coast (Australia)
  • Cairns Beaches
  • Darwin & NT Coast (Australia)
  • Ko Pha-ngan & Ko Samui (Thailand)
  • Papua New Guinea Coast
  • Philippines (Visayan Sea)
  • Sabah / Kota Kinabalu (Malaysia)
  • Whitsundays / Airlie Beach (Australia)

Medium

  • Algarve & Costa Vicentina (Portugal)
  • Bali & Lombok (Indonesia)
  • Beidaihe / Bohai Coast (China)
  • Bermuda
  • Canary Islands (Spain)
  • Cancún & Riviera Maya (Mexico)
  • Costa Brava & Balearics (Spain)
  • Côte d'Azur & Corsica (France)
  • Danish Øresund Coast (Copenhagen–Helsingør)
  • Dublin & Irish East Coast
  • Durban / KwaZulu-Natal (South Africa)
  • Exmouth / Ningaloo (Australia)
  • Galveston & Texas Gulf Coast (USA)
  • Gold & Sunshine Coast Bluebottles (Australia)
  • Israeli Mediterranean Coast
  • Jersey Shore Bays (USA)
  • K'gari / Fraser Coast (Australia)
  • Korean Coast (Nomura's Jellyfish)
  • Langkawi / Pantai Cenang (Malaysia)
  • Nha Trang & South-Central Vietnam
  • Northern Adriatic (Istria–Dalmatia)
  • Northern Isefjord & Nykøbing Sjælland (Denmark)
  • Okinawa (Japan)
  • Phuket West Coast
  • Roskilde Fjord (Denmark)
  • Sicily & Strait of Messina (Italy)
  • Sri Lanka (South & West Coast)
  • Sydney & NSW Beaches (Australia)
  • Tunisian Coast (Hammamet–Djerba)
  • Volusia County / Central Florida (USA)
  • Waikiki & South Shore Oahu (Hawaii)

Low

  • Chesapeake Bay (USA)
  • Northland & Auckland Beaches (New Zealand)

Questions

Where is jellyfish a risk?

We track 41 zones for this hazard. 8 are rated high risk, including Broome & Kimberley Coast (Australia), Cairns Beaches, Darwin & NT Coast (Australia), Ko Pha-ngan & Ko Samui (Thailand), Papua New Guinea Coast. 31 are rated medium and 2 low.

How do you avoid jellyfish?

Obey purple or jellyfish-warning flags, and swim inside stinger nets where they are provided. In northern Australia during the wet season, wear a full stinger suit rather than relying on avoidance. Never touch a jellyfish washed up on the beach — beached specimens still sting, sometimes for days.

What is the first aid for jellyfish?

Box jellyfish waters: douse with vinegar for at least 30 seconds, call emergency services immediately, and be ready to start CPR. Elsewhere: rinse with seawater — not fresh water, which fires more stinging cells — and lift off remaining tentacles with a gloved hand or a card edge. Immerse the area in hot water at about 45°C for 20–45 minutes for pain relief.

The species that matter

Box jellyfish (Chironex fleckeri) off northern Australia, Thailand, Malaysia and the Philippines can kill within minutes; they are near-invisible in the water. Irukandji are thumbnail-sized and cause a delayed, severe systemic syndrome 20–40 minutes after a mild sting. The Portuguese man o' war — not a true jellyfish — delivers a long, intensely painful sting across the Atlantic, the Canaries and the Mediterranean. Everything else is usually a local sting.

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