What to Do if You Are Stung by a Jellyfish in Hawaii
Last updated 4 July 2026. This is general information, not medical advice. If a sting is severe or the person has any trouble breathing, call 911. For treatment questions at any hour, the Hawaii Poison Center is free and confidential on 1-800-222-1222.
Stung right now? Do this first
The first aid is the same whether a box jellyfish or a Portuguese man o war got you, so you do not need to identify it before you start. Get out of the water, rinse with vinegar, then apply heat. Do not rinse with fresh water or seawater, do not rub the area, and do not use ice, all of which can make the sting worse.
- Get out of the water. A sting causes sudden pain and cramping, and the real danger in the first minute is struggling to swim back in.
- Lift off any tentacles stuck to the skin. Use a gloved hand, tweezers, or the edge of a credit card to lift them away. Do not pull them off with bare fingers and do not scrape, which drives more venom in.
- Flood the sting with vinegar for at least 30 seconds. Vinegar stops any stinging cells that have not fired yet. Lifeguard towers at Waikīkī and other guarded beaches keep vinegar on hand, which is the best reason to swim near a lifeguard.
- Apply heat. Soak the area in hot water or use a hot pack for 40 to 45 minutes. The water should be as hot as you can comfortably tolerate, around 45°C (113°F). Test it on uninjured skin first, take extra care with children, and never use scalding water. Heat breaks down the venom and is the most effective pain relief.
If you have no vinegar or hot water on the beach, get out of the water, leave the area alone, lift off any visible tentacles, and find a lifeguard, who carries both. Failing that, a hot shower back at the hotel is the next best thing. Do not pack the sting in ice.
When a jellyfish sting is an emergency
Most Hawaii stings are painful for a few hours and then fade. The box jellyfish here, Alatina alata, delivers a painful but non-lethal sting, and it is not the deadly Australian sea wasp. A small number of people react badly, though, and a rare systemic reaction can turn serious. Call 911 straight away if the stung person shows any of the following.
- Any trouble breathing, wheezing, or a tight chest or throat
- Swelling of the lips, tongue or throat, or hives spreading well beyond the sting, which point to a severe allergic reaction that can happen even in someone with no known allergy
- Chest pain, an irregular or racing heartbeat, or fainting
- Severe cramping pain in the back or abdomen, drenching sweat, nausea or vomiting
- Confusion or reduced consciousness
- A sting across a large area, a sting to the face, or a young child stung
While you wait for help, keep applying vinegar and heat, keep the person calm and still, and be ready to start CPR if they stop breathing. A sting to the eye or mouth also needs medical care. Flush the eye gently with clean water only and never put vinegar in it.
One thing makes Hawaiian stings tricky. A rare delayed reaction, with severe muscle, back, chest and abdominal pain, sweating and swings in blood pressure, can appear 4 to 48 hours after the sting, sometimes after you have left the beach. If that happens, go to an emergency room rather than waiting it out.
Vinegar, pee or ice, what actually works
Much of the real science on this was done in Hawaii, at the University of Hawaiʻi at Mānoa, and the lab findings overturned a lot of the advice people still repeat. Vinegar and heat work. Peeing on a sting, packing it in ice, and rinsing it with water all make it worse. The table below is the short version, and the UH research is the source.
| Remedy | Does it work? | Why |
|---|---|---|
| Vinegar | Yes, use it | Stops stinging cells that have not fired yet. It does not neutralise venom already injected, so it is a first step, not a cure. |
| Hot water or heat | Yes, best pain relief | Heat around 45°C breaks down the venom. Lab studies show 40 or more minutes at that temperature sharply reduces the damage. |
| Peeing on it | No | A myth that can trigger more stinging cells to fire. The same goes for alcohol, soda, lemon juice and dish soap. |
| Ice or cold packs | No, avoid | The sting burns, so cold feels right, but lab studies suggest cold helps the venom form more damaging pores in the skin. |
| Rinsing with seawater or fresh water | No | UH research on local species found rinsing spreads unfired stinging cells and worsens the sting. Some guidance elsewhere still suggests a seawater rinse for man o war, but the Hawaii advice is not to. |
| Scraping or rubbing with a towel or sand | No | Pressure fires more stinging cells. Lift tentacles off gently instead. |
What stung you, box jellyfish, man o war or sea lice
Three different creatures cause almost all Hawaii stings, and they behave very differently. The immediate first aid of vinegar then heat is the same for the first two, but knowing which is which tells you what to expect and how to plan.
| Box jellyfish (Alatina alata) | Portuguese man o war | Sea lice (seabather’s eruption) | |
|---|---|---|---|
| What it is | A true box jellyfish. A transparent, cube-shaped bell about the size of a thumb to a fist, with four tentacles. | Not a jellyfish but a floating colony called a siphonophore. A blue-purple gas float with one long trailing tentacle, often the smaller Pacific bluebottle in Hawaii. | Tiny jellyfish larvae, classically the thimble jellyfish, that get trapped under a swimsuit. |
| Where and when | South and leeward shores of Oʻahu (Waikīkī, Ala Moana, Hanauma Bay), 8 to 10 days after a full moon. | Windward, east-facing beaches such as Kailua and Lanikai when onshore trade winds blow, most often May to September. Any island. | Warm water, more common in summer, and reported far less in Hawaii than in Florida and the Caribbean. |
| The sting | Immediate sharp, burning pain and red welts, often in a whip-like line. Peaks fast. | Immediate intense pain in a long line where the tentacle touched. Can be as bad as or worse than the box jelly. | Itchy red bumps, usually under the swimsuit, appearing 4 to 24 hours after the swim rather than at the time. |
| First aid | Vinegar, then hot water or heat. | Vinegar, then hot water or heat, per UH research. | Remove and wash the swimsuit and do not wear it back in. Treat the itch with hydrocortisone or an antihistamine. Vinegar and heat are not the fix here. |
Two notes on names and hazards. Sea lice here means the larval-jellyfish rash, not the fish parasite of the same name, which does not affect people. And a stranded man o war can still sting, because its tentacles stay active for hours after it dies, so do not let children poke the blue blobs on the sand.
The Oʻahu box jellyfish calendar for 2026 and 2027
This is the part you can plan around. On south-shore Oʻahu, box jellyfish arrive on a regular schedule. The Waikīkī Aquarium’s long-running calendar puts the influx at 8 to 10 days after each full moon, month after month. Lifeguards post warning signs during an influx, and in bigger ones the City has closed Hanauma Bay to swimmers.
The windows below are calculated from the full-moon dates in Hawaii time. Days 8 to 10 are the peak, and the day before and the two days after can also see jellies.
| Full moon (Hawaii time) | Predicted box jellyfish window, Oʻahu south shore |
|---|---|
| Jun 29, 2026 | Jul 7 to 9, 2026 |
| Jul 29, 2026 | Aug 6 to 8, 2026 |
| Aug 27, 2026 | Sep 4 to 6, 2026 |
| Sep 26, 2026 | Oct 4 to 6, 2026 |
| Oct 25, 2026 | Nov 2 to 4, 2026 |
| Nov 24, 2026 | Dec 2 to 4, 2026 |
| Dec 23, 2026 | Dec 31, 2026 to Jan 2, 2027 |
| Jan 22, 2027 | Jan 30 to Feb 1, 2027 |
| Feb 20, 2027 | Feb 28 to Mar 2, 2027 |
| Mar 22, 2027 | Mar 30 to Apr 1, 2027 |
| Apr 20, 2027 | Apr 28 to 30, 2027 |
| May 20, 2027 | May 28 to 30, 2027 |
| Jun 18, 2027 | Jun 26 to 28, 2027 |
| Jul 18, 2027 | Jul 26 to 28, 2027 |
| Aug 16, 2027 | Aug 24 to 26, 2027 |
| Sep 15, 2027 | Sep 23 to 25, 2027 |
| Oct 15, 2027 | Oct 23 to 25, 2027 |
| Nov 13, 2027 | Nov 21 to 23, 2027 |
| Dec 13, 2027 | Dec 21 to 23, 2027 |
Treat this as a planning tool, not a guarantee. The Waikīkī Aquarium is clear that jellyfish can appear on any day of the year. The moon sets the biological clock, but wind, swell and currents decide whether the swarm actually reaches a beach, so a window can pass with none or jellies can turn up off schedule. Our Box Jellyfish Calendar tool gives the status for any date you choose.
Are there box jellyfish on Maui, Kauaʻi and the Big Island
Box jellyfish can turn up on any island, but the 8-to-10-days-after-the-full-moon calendar is a south-shore Oʻahu pattern. Maui, Kauaʻi and the Big Island do not follow the same reliable schedule, so there is no dependable calendar to plan around on those islands. The bigger and more year-round concern there is usually the Portuguese man o war, which the wind blows onto east-facing beaches whenever the trades are up. Wherever you are, the same rule wins. Swim at a lifeguarded beach and ask the lifeguard what is in the water that day. For the windward side, our Portuguese Man o War Forecast shows current wind-driven risk.
How long a jellyfish sting lasts
For a typical Hawaii sting, the worst of the pain comes in the first 20 to 40 minutes and eases a lot once you apply heat. Redness, welts and itching usually settle over a few hours to a couple of days. A more severe sting can leave dark or blistered welts and, occasionally, a scar or lingering skin discoloration for weeks. Delayed itching a day or two later is normal, and a mild antihistamine and hydrocortisone cream help. What is not normal, and needs a doctor, is spreading redness, warmth and pus, which signal infection, or any of the emergency symptoms above.
What treatment costs a visitor
Most Hawaii stings need no medical care at all, and vinegar and heat from a lifeguard tower are free. If you do need more, costs vary widely and can add up for out-of-state and international visitors, who usually pay upfront and claim later. An urgent-care visit is normally the cheaper option for a sting that needs a doctor but is not an emergency, while a hospital emergency room visit for a severe reaction can run into the hundreds or thousands of dollars. Two things help. Check whether your travel insurance or credit card covers out-of-state or overseas medical care before you travel, and keep receipts and discharge paperwork for the claim.
How to avoid getting stung
On Oʻahu’s south shore, avoid the 8-to-10-day window after the full moon if you can. Everywhere, look for posted warning signs and the purple dangerous marine life flag, and ask the lifeguard, who knows what is in the water that morning and carries vinegar and hot packs. A rash guard, dive skin or leggings physically block a lot of tentacle contact and are cheap insurance during a known window. A sting-inhibitor lotion such as Safe Sea, which combines sunscreen with a sting blocker, reduced stings in a controlled trial on other species in the Gulf and Caribbean, though it has not been tested against Hawaii’s box jellyfish, so treat it as an extra layer rather than a guarantee. Finally, do not touch anything blue on the sand, because beached man o war still sting.
Frequently asked questions
Should you pee on a jellyfish sting?
No. It can make the sting worse by triggering more stinging cells to fire. Use vinegar, then heat.
Can a jellyfish sting kill you in Hawaii?
It is very unlikely. Hawaii’s box jellyfish causes painful but non-lethal stings and is not the deadly Australian sea wasp. The real risks are a severe allergic reaction or a rare systemic reaction, which is why you watch for trouble breathing and call 911 if it appears.
Is Hawaii’s box jellyfish the same as Australia’s deadly one?
No. Australia’s Chironex fleckeri can be fatal within minutes. Hawaii’s Alatina alata is a smaller, far less dangerous species with no confirmed deaths from its sting.
How long does a jellyfish sting hurt?
The sharp pain usually peaks in the first 20 to 40 minutes and eases after heat treatment, with redness and itching fading over a few hours to a couple of days. Severe stings can leave welts or marks for weeks.
What does a Portuguese man o war sting look like?
A long, thin, red welt line that follows where the tentacle touched, with immediate intense pain. You may also see the animal, a blue-purple balloon-like float with one long blue tentacle.
Are there box jellyfish in Waikīkī?
Yes. Waikīkī sees the most box jellyfish stings in Hawaii, concentrated in the 8-to-10-day window after each full moon. Lifeguards post signs during an influx.
Are there jellyfish on Maui or Kauaʻi?
They occur, but without Oʻahu’s predictable calendar. On other islands the Portuguese man o war on windward beaches is the more common concern. Always ask a lifeguard.
What are sea lice and are they in Hawaii?
Sea lice is a nickname for seabather’s eruption, an itchy rash from tiny jellyfish larvae trapped under a swimsuit that appears hours after a swim. It is far less common in Hawaii than in Florida, but possible. Remove and wash the swimsuit and treat the itch, as vinegar and heat are not the answer for this one.
Do you use vinegar or hot water first?
Vinegar first, for at least 30 seconds, to shut down any unfired stinging cells. Then heat to break down the venom and relieve pain.
Why not ice, when the sting burns?
Cold feels right but lab studies suggest it helps the venom form more damaging pores in the skin. Heat is what deactivates jellyfish venom.
Can I still swim during a box jellyfish window?
Many people do, but you are accepting higher odds of a sting on south-shore Oʻahu during those days. If you swim, choose a lifeguarded beach, wear a rash guard, and check the flags and signs first. Small children and anyone with a known allergy should sit the window out.
Do lifeguards treat jellyfish stings for free?
Yes. Guarded beaches such as Waikīkī keep vinegar and hot packs at the tower and will help you treat a sting at no charge.
Related guides
- Box Jellyfish Calendar tool, which checks the risk for any date on Oʻahu’s south shore.
- Portuguese Man o War Forecast, showing wind-driven risk for windward beaches.
- Hawaii Beaches Swim Guide, with conditions and safety by beach.
- Stepped on a sea urchin or cut by coral, first aid for the other common Hawaii reef injuries.
- How Hawaii beach warnings and closures work, including the box jellyfish moon calendar.
Sources include the University of Hawaiʻi at Mānoa (Yanagihara lab, SOEST), the Waikīkī Aquarium box jellyfish calendar, peer-reviewed sting-management research, and Hawaiʻi Ocean Safety. This is general information, not medical advice. When in doubt, call 911 or the Hawaii Poison Center on 1-800-222-1222.