Can Jellyfish kill humans?


On 12th September 2015, a 31-year-old Chinese man was stung by a jellyfish while he was enjoying his vacations at Chaweng beach, Samui island. Soon after he lost consciousness. He was doused with vinegar & cardiopulmonary resuscitation was started at the hospital approximately 10 to 15 min after being stung. He was then shifted to the Intensive Care Unit and put on a respirator.

The case in discussion here is of a box jellyfish sting, a highly dangerous jellyfish responsible for fatalities on the islands of Samui and Pha-ngan in the Gulf of Thailand. Though box jellyfish sting cases are rare but life-threatening. From 1997 to 2015, 15 such cases have been reported on these islands, highest incidence during the month of August, a majority by Chironex fleckeri, a species of box jellyfish.


Box Jellyfish

Box jellyfish has a cube-shaped body with long tentacles, reaching up to 10 feet in length. It has a well developed nervous system enabling its rapid movement and fast swimming, up to 2 meters per second. With its 24 eyes, it can adapt to light and dark environment.


Chironex fleckeri, the most lethal member of Chirodropidae family has a powerful venom that can cause cardiopulmonary depression soon after the sting due to its ability to degrade cell walls. This results in a leak of potassium, leading to hyperkalemia. Death can occur within minutes after being stung. Other symptoms reported by victims include

  • Severe burning pain
  • Numbness
  • Oedema
  • Itching
  • Shortness of breath
  • Unconsciousness
  • Difficulty swallowing and speaking
  • Shivering
  • Fever
  • Irregular pulse/heart failure

Box jellyfish is transparent, disappearing in the clear waters, therefore till the time victim realises, the venom has already spread. Caterpillar tracks or ladder-like burn marks appear on the skin of the victim.

A sting victim’s leg after a Sting in the North of Koh Samui (2012) Source:

First Aid

The stinging cells on the tentacles are triggered by the chemicals of the skin, not by touch. After adhering to skin, it pumps venom, causing intense agonizing pain.

  1. Wash with vinegar for 30-60s (it deactivates nematocysts to suppress venom release).
  2. Remove the attached tentacles (Use a towel or gloved hand to remove tentacles to prevent secondary stinging, causing further envenomation.)
  3. Immerse in hot water
  4. Immobilize the affected area and maintain at a gravity-neutral level.
  5. Call out for emergency attention.
  6. Apply anti-venom if available.

Some evidence advise against the use of vinegar as it has shown to exaggerate the envenomation. Moderate pain can be alleviated with hot packs. 
For swelling and itching, mild hydrocortisone cream or an oral antihistamine can be given. Antibiotics might be necessary if the patient develops cellulitis.


  • Avoid night swimming
  • Avoid beaches or waters with a known jellyfish infestation, especially during peak seasons
  • Wear protective swim gear
  • Avoid picking up dead jellyfish
  • If a regular swimmer of fresh-water, beware of the first aid steps.
  • Avoid touching marine animals while snorkelling

Food for thought
Shouldn’t proper instructions and clear warnings be put up on the notorious beaches?


Thaikruea, Lakkana & Siriariyaporn, Potjaman. (2016). The magnitude of severe box jellyfish cases on Koh Samui and Koh Pha-ngan in the Gulf of Thailand. BMC Research Notes. 9. 108. 10.1186/s13104-016-1931-8.

Barbara J. Drobina, D. (n.d.). Jellyfish Stings Reaction, Symptoms, Pictures, and Treat. Retrieved from Emedicine Health:

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Dr. Arsia Hanif has been a meritorious Healthcare professional with a proven track record throughout her academic life securing first position in her MCAT examination and then, in 2017, she successfully completed her Bachelors of Medicine and Surgery from Dow University of Health Sciences. She has had the opportunity to apply her theoretical knowledge to the real-life scenarios, as a House Officer (HO) serving at Civil Hospital. Whilst working at the Civil Hospital, she discovered that nothing satisfies her more than helping other humans in need and since then has made a commitment to implement her expertise in the field of medicine to cure the sick and regain the state of health and well-being. Being a Doctor is exactly what you’d think it’s like. She is the colleague at work that everyone wants to know but nobody wants to be. If you want to get something done, you approach her – everyone knows that! She is currently studying with Medical Council of Canada and aspires to be a leading Neurologist someday. Alongside, she has taken up medical writing to exercise her skills of delivering comprehensible version of the otherwise difficult medical literature. Her breaks comprise either of swimming, volunteering services at a Medical Camp or spending time with family.


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