Jellyfish and Stings in Irish Waters: Species and First Aid

Most stings from Irish sea life are painful rather than dangerous. The species that cause the most trouble are the lion's mane jellyfish and, on sandy beaches near low tide, the weever fish. Get out of the water, remove any tentacles without rubbing, rinse with seawater, and ask a lifeguard for help if one is on duty. Seek medical advice for anything beyond mild symptoms.

First aid advice for stings has changed over the years and varies by species and by source, so this page sets out what Irish councils, the HSE (as quoted in the press) and university researchers have published, and flags where they differ.

Which species you are likely to meet

An HSE-sourced summary published in 2021 describes four jellyfish species that Irish swimmers see regularly, plus the common or moon jellyfish.

The mauve stinger (Pelagia noctiluca) is a separate case. University College Cork researchers describe adults as pink-mauve, with stings less severe than a Portuguese man o' war but strong reactions in some people. They add that pigment can transfer into the skin and leave a tattoo-like mark. Blooms are linked to oceanic water being pushed inshore when the coastal current along the shelf edge is weak, so they arrive in some years and not others.

Portuguese man o' war are not true jellyfish. They have washed up in large numbers on Irish shores, for example in September 2016, and are the species for which the first aid advice is different (see below).

First aid for jellyfish stings

Fingal and Dun Laoghaire-Rathdown county councils publish near-identical advice for lion's mane stings. In summary:

1. Get out of the water and away from the animal. If you are helping someone else, take care not to be stung yourself.
2. On a lifeguarded beach, go to the lifeguards. If the red flag is up, do not swim.
3. Rinse with seawater, not fresh water.
4. Remove any attached tentacles with gloved hands, a clean stick, tweezers or the edge of a credit card. Do not rub them off.
5. For pain and swelling the council advice is paracetamol or ibuprofen, and an antihistamine cream for mild itching.
6. Apply a dry cold pack, such as ice in a plastic bag wrapped in cloth, rather than ice on bare skin.
7. Keep any puncture marks clean and dry.

Both councils list what to avoid: rubbing the area, rinsing with fresh water, urinating on the sting, alcohol, tight bandages and, for the species likely in Ireland, vinegar. Symptoms they list include nausea, sweating, cramps and headaches, and they say to seek medical attention for anything more than minor discomfort. Neither page defines a threshold, so treat spreading pain, breathing difficulty, swelling of the face or lips, or feeling faint as a reason to ring 999 or 112.

Portuguese man o' war: different advice

A 2017 University of Galway study led by Dr Tom Doyle examined venom from the Portuguese man o' war. The university reported that rinsing with vinegar reduced venom delivery for that species, followed by removing tentacles and soaking the area in hot water at about 45°C for 45 minutes, or applying a hot pack. It also reported that rinsing with seawater and applying ice, long standard practice in Ireland, ranked among the worst responses for that species.

That conflicts with the council advice above, which says not to use vinegar for the stings likely in Ireland. The difference is the species. If you are confident you have been stung by a man o' war, the research supports vinegar and heat. For anything else, or if you are unsure, follow the lifeguard or the HSE-based council advice. The HSE-quoted summary gives warm water at 45°C for 20 minutes for a man o' war sting, a shorter time than the university reported, which is another reason to ask a lifeguard or pharmacist rather than rely on a number from a web page.

Weever fish

Weever fish live buried in sand with only the dark venomous dorsal fin showing. Quoting Irish Water Safety's chief executive, Afloat.ie reported in 2016 that they are found around the Irish coast on sandy seabeds in shallow water near the low-tide line, grow to around 15cm, and sting when stepped on. The article links the risk to spring tides, which expose more sand to bathers and surfers, and suggests avoiding the water for roughly one to two hours either side of low water or wearing sandals near the low-tide line.

The same article says pain is worst in the first two hours, the foot reddens and swells, numbness can follow, and irritation can last up to two weeks. For first aid it suggests immersing the foot in hot water as soon as possible (it says over 40°C, to break down the venom), painkillers, antihistamines if an allergic reaction develops, and help from a lifeguard. It is a 2016 press item, so treat the temperature as indicative and confirm with a pharmacist, GP or lifeguard. Take care that the water is hot, not scalding, because a numb foot can be burned without noticing.

Sea lice and other minor irritations

Swimmers sometimes report a rash after a swim that they attribute to sea lice. None of the Irish official pages consulted for this article describe it, so there is no verified local first aid to quote. A rash that spreads, blisters, or comes with fever or breathing problems should be seen by a GP or pharmacist.

Reducing the chance of being stung

• A wetsuit reduces the chance of being stung, according to the HSE-sourced summary, and booties help with weevers. If you swim in skins, cover the areas you can.
• Check council social media and beach notices in summer. Fingal County Council issued a lion's mane notice in August 2025.
• Look at the tideline before you go in. Stranded jellyfish are a warning that more are close by.
• Swim in a group and tell a buddy if you feel unwell afterwards. Delayed symptoms such as nausea and sweating are listed on the council pages.

For wider preparation, see the cold water safety checklist and sea swimming for beginners.