You should steer clear of a box jellyfish. The marine animal’s sting can cause serious and sometimes fatal symptoms in a matter of minutes.


Seek immediate medical treatment if you are stung by a box jellyfish.

box jellyfish amongst mangrove prop rootsShare on Pinterest
Box jellyfish (Chironex fleckeri) amongst mangrove prop roots. North Queensland, Australia. Credit: Ben Cropp/AUSCAPE

Despite their name, jellyfish aren’t fish. They’re Cnidaria, which are marine animals more closely related to creatures such as corals, sea anemones, and sea whips. All of these animals use spear-like stingers to capture their prey.

Jellyfish are composed of three only layers and have a very basic nervous system. They have no brain, heart, or blood. They use a single-opening digestive cavity both to eat and release waste.

There are different types of jellyfish. The boxed jellyfish are named for their box-like shape, which is covered in barbed, poisonous cells called nematocysts.

Facts about the boxed jellyfish

There are about 50 types of boxed jellyfish, but only a few are lethal to humans.

Facts about the boxed jellyfish include:

  • Most types that are lethal to humans live in the Indo-Pacific region and northern Australia.
  • The Australian box jellyfish (Chironex fleckeri) is considered the most venomous marine animal.
  • Chironex fleckeri, also known as the “sea wasp,” is the largest box jellyfish, measuring up to one foot in diameter with tentacles that can be as long as 10 feet.
  • The box jellyfish is difficult to see in the water because it’s translucent.
  • Most jellyfish simply float, but the boxed jellyfish can swim.
  • Unlike other jellyfish, boxed jellyfish have eyes and can see.

Read on to learn more about box jellyfish stings, their treatment, and more.

Box jellyfish have highly potent venom. The more lethal types, which belong to the class Cubozoa, release toxins with their nematocysts.

Not all cubozoan toxins are the same, but generally, they can destroy and poison human cells. If you’re stung, these toxins will be particularly poisonous to your red blood cells and your heart.

Is a box jellyfish sting deadly?

According to the Emergency Care Institute of New South Wales, if 10 percent or more of a person’s skin is affected by the venom of Chironex fleckeri, the sting becomes deadly, especially in children.

In this case, the sting can cause cardiac arrest within just a few minutes.

However, it’s not clear how many actual fatalities occur as a result of a box jellyfish sting.

A 2016 study examined box jellyfish stings on islands in Thailand and found that of 15 cases, six were fatal. However, all of those stung experienced serious symptoms within a few minutes.

Some scientists believe that not all fatalities are reported. One study cites tens of deaths per year.

Here are some ways to prevent a box jellyfish sting:

  • Avoid swimming or wading in areas with box jellyfish.
  • If you’re walking along the shore or in the water, wear water shoes.
  • Talk to locals in swimming areas that are known to have box jellyfish to make sure there haven’t been recent sightings.
  • Look for any posted signs or warnings about box jellyfish and avoid potentially infested waters.
  • Wear a bodysuit, wetsuit, or stinger suit to protect your skin when in the water.
  • Only use beaches that have lifeguards who may be able to help if you get stung.
  • Come prepared with first aid supplies and information on what to do if you’re stung by a box jellyfish.

Symptoms from a box jellyfish sting will vary depending on the severity of your interaction with the creature.

You may notice these symptoms first:

  • severe stinging or burning pain
  • red skin wounds that look like caterpillar tracks

Symptoms may then escalate to:

  • disoriented behavior from pain
  • loss of consciousness
  • back, chest, or abdominal pain
  • high blood pressure
  • elevated heart rate

In the most severe cases, a person can experience cardiac arrest, which can lead to death.

A box jellyfish sting can result in a variety of side effects. They include:

Irukandji syndrome

This condition results primarily from the sting of the species Carukia barnesi, but can also from other box jellyfish in the same family of Carybdeida such Alatina mordens, Malo maxima, Carybdea alata, Carybdea xaymacana, and Carybdea rastonii.

With this syndrome, the sting releases toxins in the human body, which increases anxiety and raises your blood pressure and heart rate. The sudden, at times extremely high rise in blood pressure, can lead to uncontrolled bleeding, fluid in the lung, and heart failure.

In addition, if you’re stung by Carukia barnesi or a similar jellyfish, you may get a local reaction initially. The more severe symptoms of irukandji syndrome can take 20 to 30 minutes to develop.

Irukandji syndrome doesn’t result from the sting of Chironex fleckeri. The sting of Chironex fleckeri and other box jellyfish can lead to heart rhythm problems and ultimately death by causing nonstop contraction of the muscles and overproduction of potassium in the blood. The lethal reaction, when severe, is usually immediate.


A sting may trigger your immune system to overreact and cause inflammation throughout your body. Essentially, the body will experience an allergic reaction to the venom.

This can lead to breathing difficulties and anaphylaxis, which is life threatening.

Skin inflammation

You may experience dermatitis following a jellyfish sting, which requires the application of topical creams.


The tracks created from jellyfish stings along your skin may fade with time but may leave a lasting scar.

A person stung by a box jellyfish needs immediate treatment. It’s important they get out of the water as soon as possible and receive first aid and lifesaving interventions.

Then you should follow the following steps:

  1. Exit the water or get the affected person out of the water.
  2. Rinse the area stung with acetic acid for at least half a minute. Many toxicologists in North America recommend using vinegar. In a study reviewing those stung by jellyfish who survived the encounter, half of them received a vinegar treatment. However, in the Indo-Pacific region, it’s better to use acetic acid first, as vinegar can make the symptoms worse.
  3. Use tweezers to remove any nematocysts and tentacles from the body. You can also do this by applying pressure with a credit card, but this pressure must be gentle to avoid releasing more toxins.
  4. Call emergency medical responders. While you wait for them to arrive, monitor the person’s pulse and watch their breathing pattern. However, if you see that the person isn’t breathing or showing signs of cardiac arrest, begin to administer CPR. Emergency responders may continue this resuscitation or administer oxygen using other equipment.

Once under medical care, the person stung by the box jellyfish may receive pain medication, antivenom, and continued treatment for breathing difficulties, including intubation and a ventilator.

First aid treatments to avoid

You shouldn’t touch or compress the sting. Additionally, avoid rinsing the area with fresh water, alcohol, or ice packs. The application of these substances can cause more toxins to come out and make the sting worse.

In addition, despite common beliefs, you shouldn’t use urine to treat the stings of box jellyfish. Like vinegar, this may make the symptoms worse.

An intravenous antivenom for Chironex fleckeri stings has been available since the 1970s. Scientists produced it from immunized sheep. However, the extent of its effectiveness isn’t fully clear.

Research shows that adding magnesium sulfate to venom at administration may improve the effectiveness.

In addition to the traditional antivenom, one researcher developed a product called Sting No More using zinc and copper gluconate. Some doctors even apply heat to the sting.

A team of researchers has also identified one medication that not only blocks venom but also reduces pain and scarring as long as you administer it within 15 minutes of the sting. It’s currently only available in injectable form.

Severe box jellyfish stings can be fatal, triggering cardiac arrest in your body within minutes. Less severe stings may only cause symptoms like pain and irritated red tracks along your body, but they may not be deadly.

It’s crucial to get treatment immediately following a box jellyfish sting to stop the spread of its venom, remove any remaining tentacles on your body, and get oxygen to support your body as it reacts to the poison.

To reduce the risk of a sting, avoid swimming in areas where these creatures may be present. If you choose to swim in areas where box jellyfish live, make sure you choose a beach that has trained lifeguards with proper first aid materials.