A jellyfish floating near the beach can look harmless. It may even appear soft enough to touch, especially when it has washed onto the sand. But touching one can cause a painful sting, and in some cases, it can lead to a serious medical emergency.
The danger comes from tiny specialized cells on the jellyfish’s tentacles. These cells can inject venom into your skin almost instantly, even when the jellyfish is dead.
Jellyfish Have Tiny Stinging Cells
Jellyfish do not sting by biting or attacking like many other animals. Their tentacles contain specialized cells called cnidocytes. Inside these cells are microscopic structures called nematocysts, which work somewhat like tiny spring-loaded harpoons.
When a tentacle comes into contact with skin, the nematocysts can fire. A microscopic tube shoots outward, penetrates the skin and delivers venom. The process happens extremely quickly, in a fraction of a second.
This is why even a brief touch can be enough to cause a sting. You do not have to grab a jellyfish or step directly on its body. Brushing against a tentacle can be enough.
The Tentacles Are the Real Danger
When people see a jellyfish, they often focus on its bell-shaped body. The greater concern is usually the tentacles hanging beneath it.
Jellyfish tentacles can contain thousands of microscopic stingers. When they touch your skin, many of these stingers can fire at once, producing burning or prickling pain, swelling, itching and distinctive marks that may resemble the shape of the tentacles.
There is another reason to keep your distance. Detached tentacles can still contain functioning stinging cells. A tentacle does not necessarily become harmless just because it has separated from the jellyfish.
A Dead Jellyfish Can Still Sting
One of the most important things to remember is that a jellyfish does not have to be alive to be dangerous.
Jellyfish sometimes wash up on beaches after dying. Their tentacles may look limp and lifeless, but the stinging cells can remain capable of firing. Touching a dead jellyfish can therefore result in a sting just like touching one in the water.
The same warning applies to pieces of tentacle that have broken off. If you find something that looks like a jellyfish or part of one on the beach, the safest option is simply to leave it alone.
Some Jellyfish Are Far More Dangerous
Not every jellyfish sting is life-threatening. Most cause local symptoms that eventually improve, but the severity depends on the species, the amount of venom delivered and how much skin was exposed.
A small number of species can cause severe reactions. Box jellyfish are particularly dangerous. The Australian box jellyfish, Chironex fleckeri, has venom that can cause paralysis, cardiac arrest and death in severe cases.
Another unusual animal that people often mistake for a jellyfish is the Portuguese man o’ war. It is actually a siphonophore, not a true jellyfish, but its long tentacles contain powerful stinging cells. Its tentacles can remain dangerous even after the animal has washed ashore.
Because you usually cannot identify the species simply by looking at it, there is little reason to take the risk of touching an unfamiliar jelly-like animal.
What Happens After A Sting
The reaction can begin almost immediately. A person may feel sharp or burning pain followed by redness, swelling and raised marks on the skin.
More serious reactions can affect the entire body. Symptoms can include nausea, vomiting, muscle spasms, dizziness, confusion, difficulty breathing and heart problems. Severe reactions can develop quickly and require emergency medical treatment.
The danger is not limited to people who deliberately touch jellyfish. Swimmers can accidentally brush against tentacles that are difficult to see in the water.
What To Do If You Are Stung
The first priority is to get out of the water so you do not become injured or drown while dealing with the pain.
Do not rub the affected area. Remaining tentacles should be carefully removed without touching them directly with bare hands. Seawater can be used to rinse away loose tentacles when appropriate. Current first-aid guidance from the American Heart Association and American Red Cross recommends nonscalding hot-water immersion or irrigation to help relieve pain after the tentacles have been removed.
There is some disagreement over vinegar because its effects can depend on the jellyfish species and location. For this reason, it is better to follow local beach or medical guidance rather than assuming vinegar is appropriate for every jellyfish sting.
Do not rely on popular remedies such as urine, rubbing the skin, scraping the area or pouring cold freshwater over the sting. These methods are not recommended and some can make the injury worse.
If the person has difficulty breathing, signs of shock, severe pain, chest symptoms or other serious whole-body symptoms, emergency medical help is needed. A sting involving the eye also requires prompt medical attention.
