Most people who are stung by a jellyfish only realize a jellyfish was nearby after the sting has happened. In this way, a sting might seem to come out of nowhere.

Most jellyfish stings are painful but not dangerous. A few jellyfish, however, release powerful venom into the skin. The stings of these species, if left untreated, can be dangerous or even deadly.

Prompt jellyfish sting treatment can quickly alleviate pain and prevent a sting from getting worse.

Jellyfish can be tiny or enormous, and they come in all shapes and sizes. Some have tiny stinging cells called nematocysts in their tentacles. A sting from a nematocyst can be mildly annoying, extremely painful, or even life-threatening.

Signs of a dangerous jellyfish sting

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The majority of jellyfish stings are not serious, but some species may have potentially fatal stings.

Most jellyfish stings are painful, but not dangerous. But for people with jellyfish allergies, individuals with compromised immune systems, the very old, or the very young, a sting can be dangerous.

Any signs of shock or an allergic reaction warrant prompt emergency care. Warning signs include:

  • difficulty breathing
  • dizziness
  • a rapidly spreading rash
  • nausea
  • changes in consciousness

Anyone experiencing these symptoms should call 911 or go to an emergency room right away.

A handful of jellyfish and animals that resemble jellyfish are potentially lethal, particularly after multiple stings.

However, deaths from the jellyfish are extremely rare. For example, the most dangerous jellyfish variety, the Australian box jellyfish, only kills a few people each year. If you are concerned about a sting, it is important to leave the water, as fast as possible. Many deaths associated with jellyfish are actually a result of drowning following the muscular spasms that occur after a sting.

A jellyfish’s tentacles contain venom that, at worst, can destroy the cardiovascular system in just a few minutes. Poisonous jellyfish are most prevalent in waters off the coast of Australia, so swimmers stung by jellyfish in this region should consider seeking prompt emergency care.

People with other allergies, particularly to insect stings, may be more vulnerable to an allergic reaction to jellyfish. People with allergies should always carry an adrenaline injection pen, and any other allergy medication a doctor has prescribed.

When sting victims do not see the jellyfish, it is not possible to immediately determine whether the source of the sting was harmless or potentially deadly.

Someone should seek immediate medical care if:

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Jellyfish stings that are accompanied by symptoms such as nausea, breathing problems, or loss of consciousness, will require immediate medical attention.
  • there have been reports of highly venomous jellyfish in the area
  • the jellyfish was very large
  • there are numerous tentacles at the site of the sting, as this means more venom might have been delivered
  • the sting was to the eye or mouth
  • there are signs of a severe reaction, such as difficulty breathing, a rapid heart rate, loss of consciousness, or muscle spasms
  • a rash appears on any area of the body, even if it is not near the location of the sting

First aid for minor jellyfish stings

A 2017 study found that a simple process can reduce the pain of jellyfish stings. The study looked specifically at lion’s mane jellyfish, which have large tentacles, causing very painful stings. However, the research is probably applicable to most jellyfish stings.

The following steps should be followed, as quickly as possible, following the sting:

  1. Thoroughly rinse the affected area with vinegar or with a commercial spray if available.
  2. Remove the tentacles while still rinsing. The tentacles can keep stinging as long as they are in contact with skin, so wear gloves or put plastic bags on the hands.
  3. Apply a heat pack or immerse the affected area in water of a temperature at least 113 °F for 40 minutes.

If vinegar and hot water are unavailable, carefully remove the tentacles.

After being stung by a jellyfish, stay out of the water for the rest of the day, as salt water may make the pain worse. More importantly, there are likely other jellyfish in the area.

When a jellyfish tentacle punctures the skin and draws blood, the wound can become infected. People who are not up-to-date on their vaccinations may also need a tetanus shot. It is important to see a doctor within a few hours if there is an open wound.

Some jellyfish stings cause pain and itching for a few days. Some home remedies can help. These include:

If the area becomes very painful, starts swelling, or there are streaks coming out of the wound, there could be an infection. In this case, a person should see a doctor within 24 hours.

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Some popular home remedies for jellyfish stings include urinating on the sting, or using lemon juice. These may potentially worsen symptoms, and are best avoided.

A popular myth is that urinating on a jellyfish sting can neutralize the venom. In fact, urine can make the pain worse. In some cases, urine may even make the venom more potent.

Other folk remedies, such as lemon juice and shaving cream, are also ineffective.

A Cochrane Review looked at other purported jellyfish sting treatments. It confirmed that hot water could help with pain. Some studies included in the review found that cold packs might also help, but heat was most effective.

Do not rinse the area with cold water while stingers are still in the skin since this can cause them to release more venom.

Some people use baking soda to neutralize the venom of a jellyfish sting. A 2007 study found no benefits to this approach. There is no evidence that baking soda is dangerous but other treatments are more effective.

In cases of severe stings, causing cardiovascular symptoms, an injection of magnesium sulfate may be given by a doctor in a monitored setting.

The easiest way to avoid jellyfish stings is to stay out of ocean water.

Some beaches with a jellyfish problem will post jellyfish warnings during the most dangerous times of the year. When swimming in areas where venomous jellyfish may live, people should follow these warnings and stay out of the water.

Wearing a wetsuit can protect against jellyfish stings. Foot-scuffing in shallow water may scare off jellyfish and some other stinging sea creatures.

A new jellyfish deterrent cream may also help. Called Safe Sea, the product mimics chemicals the clown fish produces. These chemicals deter jellyfish stings. The manufacturers also claim that the product can disarm jellyfish tentacles in the event of a sting.

Though this lotion may reduce the risk of a surprise jellyfish attack, it is still a good idea to avoid water where jellyfish are visible or where dangerous jellyfish have been seen.