What to do if you are stung by a jellyfish

Telegraph

17-04-2025

Sun, sea, sand – and stings. Spain's tourism trifecta is facing an unwelcome addition this summer, as jellyfish populations surge around its southern coast and islands. Earlier this month, locals described beaches on the Costa Blanca and Gran Canaria as 'carpeted' with dead jellyfish, and authorities warned of a species that delivers 'a powerfully painful sting'.
Spain is far from alone: officials in Turkey, Mexico and Australia have issued similar cautions in recent weeks – so should holidaymakers be worried? While a jellyfish isn't, perhaps, an ideal swimming companion, how dangerous are they – and what to do if you're stung? Here, three jellyfish experts share their advice.
What are jellyfish?
'They are very simple organisms,' explains Alexandra Bulgakova, jellyfish expert and Seasearch data analyst at the UK's Marine Conservation Society (MCS). 'They don't have brains, hearts or lungs. They can be as small as one to two centimetres, while the largest species – lion's mane – can grow up to two metres wide and have tentacles as long as 36 metres.'
Tentacles deliver the venom for which jellyfish are notorious, via cnidocytes – or 'stinging cells'. However, of the 3,000 global species of jellyfish, many pose no threat to humans.
One species surging in Spain, the Portuguese man o' war, isn't actually a jellyfish at all. It's 'a type of colonial hydrozoan', says Bulgakova – but it still has 'a powerfully painful sting'.
Which jellyfish are the most harmful, and where are they found?
'Box jellyfish are the most dangerous,' says Juli Berwald, ocean scientist and author of Spineless: The Science of Jellyfish and the Art of Growing a Backbone. 'There are about 50 [box] species; the most harmful are found near Australia, Philippines, Indonesia and Papua New Guinea.'
The largest box, Chironex fleckeri, is considered the most toxic: 'It's said to have enough toxin to kill 60 people,' says Berwald. 'But to put that in context, since 1884 it has been responsible for 64 deaths in Australia while the number of people who die from mosquito[-borne diseases] is about a million per year.'
Other hotspots include Okinawa (Japan) and throughout South-East Asia, says Cheryl Lewis Ames, professor of applied marine biology at Tohoku University in Sendai, Japan. Ames's lab is developing a jellyfish warning system with Covid-style rapid tests and an app to help prevent harmful stings. 'Unfortunately, many [jellyfish-related] deaths happen in South-East Asia,' she explains.
Where am I mostly likely to encounter jellyfish?
'Jellyfish occur around the world,' says Ames, 'from beaches to deep-sea environments. Europe has several kinds, particularly in the Mediterranean.' Painful ones to avoid in the Med include mauve stingers and barrel jellyfish.
Last year, 7,500 people in Spain sought medical assistance for jellyfish stings, a 41 per cent increase on the previous summer – and several beaches closed.
Authorities in Murcia have proposed installing jellyfish nets on its beaches this summer, a precaution already taken in parts of Greece, Australia and Thailand.
The Gulf of Mexico and the Caribbean also feature Portuguese men o' war and some dangerous box jellyfishes – as well as Linuche, whose sting 'can cause rash and welts all over swimmers' bodies during warm-water induced swarms', warns Ames.
Do we get jellyfish in the UK?
We do – but while their stings can be painful, there are no verified cases of jellyfish-related deaths in UK waters, says Bulgakova. 'Jellyfish can be found around most parts of the UK, with sightings most common between April and October.'
The severity of their sting varies according to the species, she adds. 'Barrel, blue and moon jellyfish have mild stings, but compass, mauve stinger and lion's mane can be more painful. [The] Portuguese man o' war, found most commonly in the Isles of Scilly and Cornwall but also as far north as Cumbria, can be seen from September to December.'
Is climate change causing jellyfish numbers to rise?
The impact of climate change on jellyfish populations 'remains a bit fuzzy', says Berwald. 'Jellyfish survive better in lower oxygen conditions than other animals, and a consequence of warmer water is lower oxygen. Some species seem to reproduce more frequently in warmer water, but the connection to climate change remains hard to pin down.
'Other human actions may be more important. Jellyfish seem to survive better in polluted water than other animals. And overfishing may be removing both their predators and competition for the smaller plankton that they eat.'
What should I do if I'm stung by a jellyfish?
Happily, it isn't asking someone to wee on you – despite what popular culture might have you believe. 'Don't panic: most jellyfish stings are not emergencies,' advises the MCS. 'If you're swimming, get out of the water and tell a lifeguard.'
To treat the sting, follow the NHS guidance, which includes rinsing the area with seawater, removing spines with tweezers or the edge of a bank card, and taking painkillers. The Australian Red Cross also recommends dousing tropical jellyfish stings with vinegar.
You should go to hospital 'if you've been stung in a tropical country', the NHS advises, or if the pain doesn't ease, or if you've been stung 'on your mouth, throat or near your eyes'.
How can I protect myself from jellyfish?
Swim in a long-sleeved top and leggings, says Berwald. 'Stinging cells are only about as long as the thickness of a sheet of paper so they won't get through [the fabric]. I've also tried a [sting-protecting] sunscreen called Safe Sea in a bloom of jellyfish, which worked well.'
Keep an eye out for signposts or flags on the beach: 'In the US, a purple flag means jellyfish are in the water,' says Berwald.
What should I do if I see jellyfish?
Keep your distance, and inform a lifeguard. Before your holiday, research what the most common (and most dangerous) local types look like. For example, the man o' war is 'visually distinctive', says Bulgakova, 'with a large translucent purple/blue float or balloon, the crest tipped with pink, and long blue-violet tentacles'.
Websites such as Perseus, Meduseo and Jellywatch allow you to report sightings, and can help you identify species. Be careful of dead jellyfish on the beach, as they may still sting.