Medicine Planet: Swimming With Jellyfish

Depending on your destination, the possibility of encountering jellyfish or other stinging sea creatures can become a concern if you are planning to swim or dive in the ocean.

Though the severity of stings and the toxicity of different species can vary, the treatment procedure is the same in general. However, it is extremely helpful to know ahead of time which decontaminants work specifically for the stingers in the region where you will be at risk.

Before You Go

If the jellyfish problem is severe at your destination, consider bringing and using a nylon dive suit.

Consider using the recently developed jellyfish-sting-protection cream (SafeSea).

Take jellyfish warnings seriously.

Find out which kind(s) of jellyfish you might encounter, and bring the appropriate decontaminant(s) with you.

Important Information

If you must rinse a sting with fresh water (and not seawater), make sure to use a forceful stream in order to remove the microscopic stinging cells without causing them to release more venom.

If the sting is over a large area, or if the victim is very young, very old, or shows signs of generalized illness (nausea, vomiting, weakness, shortness of breath, chest pain, and the like), seek help from a doctor immediately.


“Jellyfish” is the term commonly used to describe an enormous number of marine animals that are capable of inflicting a painful, and occasionally life-threatening, sting. Jellyfish are part of the grouping that also includes fire coral, hydroids, sea wasps, and anemones.

The stings occur when the victim comes into contact with the creature’s tentacles or other appendages, which may carry millions of microscopic stinging cysts, each equipped with a toxin-laden, microscopic stinger. Depending on the species, size, geographic location, time of year, and other natural factors, stings can range in severity from mild burning and skin redness, to excruciating pain and severe blistering with generalized illness (nausea, vomiting, shortness of breath, muscle spasms, low blood pressure, and so on). Tentacles that have broken off and are fragmented in the surf or washed up on the beach can retain their toxicity for months and should not be handled, even if they appear to be dried out and withered.

The dreaded box jellyfish or sea wasp (Chironex fleckeri) of northern Australia and the Indo-Pacific contains one of the most potent animal venoms known. A sting from one of these creatures can induce death in minutes from cessation of breathing, abnormal heart rhythms, and profound low blood pressure (shock).

To prevent jellyfish stings, an ocean bather or diver should wear, at a minimum, a synthetic nylon-rubber (Lycra, from DuPont) dive skin. A new sun-block cream (SafeSea, from Nidaria Technology Ltd) incorporates a substance that has been shown to prevent certain jellyfish stings, and may be effective against others — perhaps even all — by disabling the creatures’ sensing and stinging mechanisms. (The company does not test on animals and so its product has not been tested for its effectiveness against box jellyfish venom or that of other highly toxic species.)

Immediate Treatment of Stings

The following therapy is recommended for all unidentified jellyfish and other creatures with stinging cells, including box jellyfish (sea wasp), Portuguese man-of-war (“bluebottle”), Irukandji, fire coral, stinging hydroid, sea nettle, and sea anemone.

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