Box Jellyfish Stings: Everything You Need to Know

Learn more about the world's deadliest sting

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There are more than 40 species of box jellyfish, and eight of them are deadly. Though most box jellyfish stings are not life-threatening, some can kill in as little as five minutes. Quick treatment is essential to saving life.

This article describes the symptoms, treatment, and complications of box jellyfish stings.

Box jellyfish underwater

David Fleetham / Getty Images

Jellyfish Stings

Of the many species of jellyfish, eight are known to be capable of causing death.

The most venomous of all is the Chironex fleckeri, or the Australian box jellyfish. It can weigh up to 4 pounds, with dozens of tentacles that reach up to 10 feet. Each tentacle is covered with button-like structures loaded with thousands of poisonous "darts" that reach their target in a millionth of a second and deliver toxin to the victim.

Box jellyfish have 24 eyes and are the only jellyfish that can see. They swim rather than drift, so they are adept predators.

Box jellyfish are mainly found in tropical waters around Australia, Thailand, and the Philippines, but also near Hawaii, Florida, the Caribbean, Puerto Rico, and other warm, tropical places.

Box jellyfish are responsible for up to 40 recorded deaths each year, but some experts believe true figures are far higher.

Medical Emergency

If you suspect a box jellyfish sting, call 911 immediately. Most box jellyfish stings are not deadly, but they can be fatal or cause severe distress. If the person is not breathing, administer cardiopulmonary resuscitation (CPR) if possible until emergency medical personnel arrive.


Box jellyfish stings are extremely painful. Some symptoms can arise hours to weeks after a sting, but the most deadly appear immediately. They include:

  • Red whip-shaped lesions on the skin called "wheals"
  • Blistering and burning at the site of the sting
  • Severe abdominal pain
  • Chest pain
  • Shock
  • Fever or chills
  • Muscle spasms
  • Sweating
  • Nausea or vomiting

When a sting is fatal, death is usually due to cardiac arrest. Experts think the poison affects the heart directly.


It's best to treat any painful jellyfish sting rapidly and seriously, even if you don't know what kind stung you. While some kill within minutes, other box jellyfish stings can lead to death in four to 18 hours.

If you witness a box jellyfish sting, immediately do the following:

  • Help the person exit the water and try to keep them calm.
  • Call 911 or other emergency medical personnel.
  • Put hot water, vinegar, or baking soda on the sting, if available. If not, put salt water on it. That will help stop the release of venom. Avoid fresh water.
  • Remove any tentacles that you see in the skin. Do this with a knife, tweezers, or some other sharp object. Only use your hands if covered with rubber gloves—never use your bare hands.
  • If the person is unconscious, start CPR if you know how to do it.

Medical professionals can perform resuscitation, which may keep the person alive until the reaction to the venom weakens.

Experts in Australia developed an antidote to the most deadly form of box jellyfish sting, which works in about 15 minutes, but getting it to victims in time is a challenge.

What Not to Do

It's important to know what you shouldn't do as well as what you should do in the event of a box jellyfish sting, such as:

  • Do not touch or press on the site of the sting.
  • Do not rinse with fresh water, alcohol, or ammonia (urine), which could spread the venom.
  • Do not ignore it and wait for the pain to go away. Serious complications can still arise hours or days after a sting.

Should I Pee on a Jellyfish Sting?

Despite popular belief, peeing on a jellyfish sting isn't recommended. In fact, it may even increase pain.


Reactions to box jellyfish stings can be immediate or delayed by several days or even weeks. Complications may include the following.

Irukandji Syndrome

Some box jellyfish stings cause Irukandji syndrome, a group of symptoms that begin 20–30 minutes after the sting and progress over a few days. The syndrome is not typically fatal, but it can make you seriously ill, and some people do die from it.

Symptoms include:

  • Pain
  • Muscle cramping and spasms
  • Sweating
  • Shaking
  • Nausea and vomiting
  • Rapid heart rate
  • High blood pressure

In very serious cases, a person may experience cardiogenic shock or a pulmonary edema.

Irukandji syndrome often requires hospitalization, so if you have been stung by a jellyfish, pay close attention to symptoms that may arise sometime afterward.

Delayed Allergic Reaction

Some stings can cause an allergic reaction that doesn't appear for a week or two or even longer. It can cause a rash, blisters, or other kinds of skin irritations.

Your healthcare provider can give you topical or oral treatments to address the condition.


A box jellyfish's tentacles can leave permanent scars, including keloids, which are raised areas of scar tissue. There may be changes in skin color, and lichenification, in which the skin becomes thick and leathery in appearance. In some cases, areas of the skin die.


Some actions you can take to reduce the chance of a box jellyfish sting include:

  • Avoid swimming in areas where jellyfish are common.
  • Wear a wetsuit and waterproof swimming shoes.
  • Be alert for warnings that jellyfish are in the area. Sometimes they swarm.
  • Don't touch jellyfish that have washed up on land; the tentacles are still poisonous.
  • Stay away from any jellyfish you see in the water.
  • Swim near a lifeguard, who can offer first aid and call an ambulance if necessary.


Box jellyfish, usually found in tropical or warm waters, are one of the most venomous creatures in the world. There are dozens of kinds of box jellyfish, and some species are deadly.

If someone is swimming in warm waters and has severe pain, trouble breathing, or loses consciousness, they may have been bitten by a jellyfish. If so, call 911 immediately. In the meantime, you can cover the site of the string with vinegar, baking soda, or hot water. Administer CPR if you are certified.

A Word From Verywell

Though only a small percentage of box jellyfish stings are fatal, when they are, they kill quickly. Even nonfatal stings can have serious complications. Therefore, you should take any jellyfish sting seriously. If you witness symptoms of a jellyfish sting, call an ambulance right away. Doing so could save a life.

Frequently Asked Questions

  • How long does it take for the symptoms of a box jellyfish sting to start?

    There are two kinds of reactions to a box jellyfish sting. Some are immediate, including severe pain and life-threatening symptoms. Others take hours or days to appear and may include pain and other signs or symptoms that require hospitalization. A delayed allergic reaction can take up weeks or more.

  • Can you survive a box jellyfish sting?

    Most box jellyfish stings are not lethal, though they may be painful and cause an array of symptoms that need urgent medical attention. However, certain box jellyfish stings, like the Chironex fleckeri, can be fatal in a matter of minutes.

  • Where are box jellyfish found?

    Box jellyfish tend to be found in warmer, tropical waters around the world, such as off the coast of Australia, Thailand, the Philippines, Florida, and the Caribbean. Most often they are found in the Indo-Pacific.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Nancy LeBrun
In addition to her extensive health and wellness writing, Nancy has written about many general interest topics for publications as diverse as Newsweek, Teen Vogue,, and Craftsmanship Quarterly. She has authored a book about documentary filmmaking, a screenplay about a lost civil rights hero, and ghostwritten several memoirs.