Jellyfish Sting

There are thousands of species of jellyfish around the world. Most jellyfish stings are harmless, but some can cause serious harm. Seek immediate medical help if you’re experiencing any life-threatening symptoms, such as difficulty breathing. But you can treat most jellyfish stings with a few basic first aid steps.

Overview

What is a jellyfish sting?

Jellyfish are sea creatures that live in all of the world’s oceans. They have soft, bell-shaped bodies with lengthy, finger-like structures called tentacles. Jellyfish have stinging cells called nematocysts inside of their tentacles. A single tentacle may contain thousands of nematocysts.

Nematocysts contain a poisonous substance (venom) that helps jellyfish protect themselves. The venom also helps them capture food by stinging it. Jellyfish don’t usually mean to sting humans. They sting when you brush up against them while swimming or walking along the beach.

Most jellyfish stings are harmless. But some jellyfish stings can cause serious harm. If you or someone you’re with is stung, get help right away. If you’re experiencing life-threatening symptoms such as difficulty breathing, call 911 or go to your nearest emergency room.

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How do jellyfish sting?

Jellyfish don’t intentionally mean to sting humans. But if you brush by one or accidentally step on one, it stings you to protect itself.

Each nematocyst in a jellyfish’s tentacle contains spring-loaded barbed threads, or tubules. When triggered, a large concentration of calcium passes over the jellyfish’s plasma membrane. This leads to increased pressure inside the nematocyst. The increased pressure causes the threads to uncoil and spring out like tiny darts, firing venom into an unsuspecting victim. The entire process takes a fraction of a second.

Moreover, nematocysts can fire their venom even when they’re unattached from the jellyfish. They can also fire their venom if the jellyfish is dead.

How common are jellyfish stings?

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As many as 150 million jellyfish stings occur around the world each year.

How does a jellyfish sting affect my body?

The reaction you receive from a jellyfish sting depends on many variables. Some jellyfish stings only cause minor irritation, and some stings can be fatal. The factors that influence what type of reaction you may have include:

  • Type of jellyfish.
  • Your age, health and body weight.
  • Where on your body you were stung.
  • The surface area of your exposed skin.
  • How long the venom has been in your body.

What types of jellyfish can cause serious harm?

There are thousands of different types of jellyfish in the oceans around the world. While some can be harmless, there are others you need to watch out for and avoid. Some of the jellyfish whose stings can cause serious harm include:

Box

The box jellyfish is the most deadly jellyfish in the world. Sometimes called sea wasps, they have box-like bodies with tentacles extending from each corner. Box jellyfish live in tropical areas around the world. They’re commonly found on the northern coast of Australia and the Indo-Pacific Ocean. There are more than 40 species of box jellyfish. The Australian box jellyfish is the most venomous jellyfish in the world.

Lion’s mane

The lion’s mane jellyfish is the largest jellyfish in the world. They can grow up to more than 3 feet wide, and their mane-like tentacles can grow up to 120 feet long. Lion’s mane live in cooler climates in the Arctic Ocean and the North Pacific Ocean. Their name comes from the hundreds of sting-covered tentacles that make up their mane.

Sea nettle

The sea nettle jellyfish is one of the most common jellyfish found along the Atlantic, Pacific and Gulf coasts. They’re another large jellyfish that can grow more than 1 foot wide. Each sea nettle has 24 tentacles that can grow up to 6 feet long.

Portuguese man-of-war

The Portuguese man-of-war isn’t technically a jellyfish, but they look like one. These creatures live in the tropical waters of the Atlantic, Pacific and Indian oceans and the Caribbean Sea. Portuguese man-of-war have balloon-like floats that keep them above the water. Below the water, they have long strands of tentacles and polyps that grow to about 30 feet long.

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Symptoms and Causes

Minor symptoms of a jellyfish sting may include slight pain, itching and a rash. More serious stings can cause severe symptoms such as difficulty breathing.
Symptoms of a jellyfish sting depend on the type of jellyfish you made contact with.

What are the symptoms of a jellyfish sting?

The symptoms of jellyfish stings depend on the type of jellyfish you made contact with. If you have a minor jellyfish sting, you may feel slight pain, itching, burning or throbbing. A jellyfish sting may look like a rash with red, purple or brown patches.

More serious jellyfish stings can cause greater harm. You should seek medical help right away if you have more severe symptoms. These symptoms may include:

What causes a jellyfish sting?

You may come into contact with the nematocysts of a jellyfish when you’re swimming in the ocean or walking on the beach. This contact can cause a jellyfish to inject its venom from the nematocysts into your body. The venom affects your skin and can also enter your bloodstream.

Depending on the type of jellyfish and how much of your skin touches the venom, the sting can cause pain or other serious health problems. Some jellyfish stings can be life-threatening. It’s important to get medical help if you have severe symptoms after a jellyfish sting.

Diagnosis and Tests

How are jellyfish stings diagnosed?

Most jellyfish stings don’t require medical care from your healthcare provider. If you do seek treatment, your healthcare provider will probably be able to diagnose a jellyfish sting by looking at it. You may still have stingers in your injury. If so, your healthcare provider may collect a sample of the stingers to determine the appropriate treatment.

Management and Treatment

How is a jellyfish sting treated?

Most people don’t need to see their healthcare provider for a jellyfish sting. Depending on the type of jellyfish, you can administer first aid for most stings. You can treat mild jellyfish stings using the following steps:

  1. Wash the tentacles and venom off the affected area of your body with seawater. Don’t use freshwater.
  2. Using tweezers or gloved hands, remove any tentacles you see in your skin.
  3. Apply vinegar or rubbing alcohol to the affected area to stop any more firings of nematocysts. (You shouldn’t use vinegar for Portuguese man-of-war stings, though. It can cause more venom to be released from the nematocysts.)
  4. To help reduce the pain, you can put calamine lotion or hydrocortisone cream on a jellyfish sting. You can also use an ice pack or hot water to help with the pain and swelling.

If you seek medical care, your healthcare provider may treat more serious jellyfish stings with medication. Medications your healthcare provider may use include:

  • Pain relievers: Pain relievers can help reduce your pain.
  • Antivenin: Antivenin can help reverse the effects of the venom.
  • Antihistamines: Antihistamines can help reduce itching and rash.

Does peeing on a jellyfish sting help?

No. You shouldn’t pee on a jellyfish sting. This old wives’ tale for how to cure a jellyfish sting has been around for a long time. The myth goes that if you apply urine to a jellyfish sting, you’ll counteract the venom. But no scientific studies back up this claim. In fact, peeing on a jellyfish sting could actually make the sting hurt worse.

Prevention

How can I prevent a jellyfish sting?

A jellyfish can sting you anytime they’re in or near the ocean, like on the beach. To reduce your risk of being stung:

  • Ask lifeguards or park rangers if any jellyfish are present around your beach. (Some beaches post a warning flag when jellyfish are reported.)
  • If you surf or dive in the ocean, wear a protective bodysuit.
  • Never touch a jellyfish that’s washed up on shore. Dead jellyfish still have venom in their tentacles that can sting on contact.

Outlook / Prognosis

How long does a jellyfish sting last?

Most jellyfish stings improve within a few hours. But some jellyfish stings can lead to rashes that can last for weeks. Once the rash goes away, you may be left with a permanent scar from the jellyfish sting. Contact your healthcare provider if the sting site continues to itch after a few weeks.

What is the outlook for a jellyfish sting?

The prognosis for a jellyfish sting depends on the type of jellyfish. Stings from some jellyfish cause only minor itching and pain. But some box jellyfish stings can kill you within a matter of minutes. Other box jellyfish stings can cause a fatal reaction four to 48 hours after a sting due to Irukandji syndrome. Irukandji syndrome is a delayed reaction to a sting.

Living With

When should I see my healthcare provider about a jellyfish sting?

If you’re been stung by a box jellyfish, it’s important to carefully monitor your symptoms for hours after the sting. Seek medical attention right away for any severe symptoms. This includes breathing difficulties, chest or abdominal pains, or profuse sweating.

Additional Common Questions

Do all jellyfish sting?

All jellyfish have tentacles, but they don’t all have powerful stinging nematocysts. For example, moon jellyfish live in all of the world’s oceans. Moon jellyfish don’t have long, poisonous tentacles. They have hundreds of short, fine tentacles. While the moon jellyfish will sting if you brush against it, the sting is usually mild and you’ll probably only have a slight reaction to it.

A note from Cleveland Clinic

There are thousands of species of jellyfish in the oceans around the world. Jellyfish don’t mean to sting humans. But they can sting you when you brush up against them while swimming or walking along the beach. Most jellyfish stings are harmless. But some jellyfish stings can cause serious harm. If you, or someone you’re with, are stung, get help right away. If you’re experiencing life-threatening symptoms such as difficulty breathing, call 911 or go to your nearest emergency room.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 06/07/2022.

Learn more about our editorial process.

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