How Do Jellyfish Sting?

While taking a casual swim at the beach, you feel something gently brushing against your arm. At first, you ignore it, because you are already surrounded by water and there are many sensory inputs to distract you from the feeling. However, after a while, you experience a searing pain at a specific point on your arm, which soon starts to spread across your entire hand. It’s only then that you realize…

you've been stung by a jellyfish meme


Planet Earth is filled with weird creatures. Apart from humans, one that never fails to catch my attention is jellyfish. Contrary to what its name might suggest, it’s not actually a fish. It is a type of plankton, and a distant relative of corals and sea anemones. Apart from the fact that it’s composed of 98% water and is made of a translucent gel-like substance (called mesoglea), it neither has a brain nor a heart!


Photo Credit: bierchen / Shutterstock

Given that fact, how on Earth is a jellyfish able to sting innocent people swimming and minding their own business at beaches across the globe?

How do jellyfish sting?

Like other creatures, jellyfish also have to survive and thrive in this beautiful, but sometimes unforgiving world. In order to prevent themselves from perishing due to lack of food or being easily captured by a predator, they are equipped with thousands of special stinging cells called cnidocytes along their tentacles. Venom from these cnidocytes is injected into a foreign body through a whip-like hollow tubule (called a nematocyst) that contains a barbed or venomous coiled thread, and lies prepared to attack under high osmotic pressure (the minimum pressure that needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane).

Jellyfish stinging a diver

The tiny harpoon-like stingers inject venom when something comes in contact with them

The moment something comes close enough to the jellyfish to activate the external trigger, the lid of the cell bursts open. This causes seawater to fill in the cell, which in turn ejects the barbed harpoon-like structure and injects the venom into the victim. In short, it stings!

The fascinating thing about this entire offensive-cum-defensive system is that it happens incredibly fast; once triggered by the touch of a human, a jellyfish stinger can penetrate the skin in a millionth of a second – less than the time it takes to blink your eye!

Things to keep in mind in the event of a jellyfish sting

Avoid cleaning the wound with freshwater

Don't clean Jellyfish stings with freshwater

Cleaning Jellyfish stings’ wounds with freshwater is not a good idea

It’s definitely not a good idea to clean the wounds of a jellyfish sting using freshwater, as the salinity of freshwater is lower than seawater, and any change in the salt balance messes with the osmotic pressure outside of the cnidocyte, which in turn fires the venom-laden harpoons deeper into the skin.

Remove the sting quickly

Since nematocyst discharge (firing of the poison-laden harpoons) is one of the fastest biomechanical processes in nature, it is highly recommended to remove the tentacles stuck to your skin to avoid further stinging. Furthermore, these stings can continue to fire, even after the jellyfish that stung you has died. Therefore, don’t assume that a downed jellyfish is harmless once you come out onto the sand. The best approach is to get rid of all the lingering tentacles as soon as you leave the water.

Does urine help?

Thanks to a number of references in movies and TV shows, many people believe that urinating on the affected area of a jellyfish sting can help alleviate the pain and discomfort. So, is it true?

no meme

No, this is actually not true… depending on how much salt the urine contains. You see, you don’t want to alter the salt balance near the stinging cells, for the reason mentioned above (e.g., pouring freshwater on the sting). Since the chances of someone knowing the exact salt content in their urine are extremely small, you can never truly know for certain if their urine would help or actually make things even worse!

What should you do in case of a jellyfish sting?

Rinsing the wound with vinegar helps to prevent further discomfort by suppressing the undischarged nematocysts. Similarly, soaking the wound in seawater can also help in ridding the skin of residual nematocysts. These are some of the first things you can do on your own (without aggravating the problem) before medical help arrives.

There are certain species of jellyfish (like sea wasps) whose venom in large doses can be deadly. However, most jellyfish stings, although quite annoying and painful, aren’t usually life-threatening and can therefore be tackled without much difficulty.


  1. Wikipedia
  2. Howstuffworks
  3. Smithsonianmag
  5. CiteSeerX – Penn State University
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Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spends a lot of time watching movies, and an awful lot more time discussing them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly Science dictates every aspect of life… in this universe, at least.

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