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.

If a topical decontaminant (vinegar or isopropyl [rubbing] alcohol) is available, pour it liberally over the skin or apply a saturated compress. (Some authorities advise against the use of alcohol on the theoretical grounds that it has not been proven beyond a doubt to help. However, many clinical observations support its use. Since not all jellyfish venom is the same, it is extremely helpful to know ahead of time what works for the stingers in your specific geographic location. Consult local authorities for this information.)

Until the decontaminant becomes available, you can rinse the skin with seawater. If you rinse with fresh water, make sure to use a forceful stream in order to remove the microscopic stinging cells physically. Gentle, nonforceful application of water or ice is more likely to cause the cells to fire, increasing the envenomation.

Special Instructions for Immediate Treatment of Box Jellyfish Stings: If the sting is thought possibly to be from the box jellyfish (Chironex fleckeri) — because of the geographic location where the injury occurs and the pattern of injury — immediately flood the wound with vinegar (5 percent acetic acid). Keep the victim as still as possible. Continually apply the vinegar until the victim can get medical attention. If you are out at sea or on an isolated beach, allow the vinegar to soak the tentacles or stung skin for 10 minutes before you attempt to remove any adherent tentacles or further treat the wound.

After decontamination, apply the pressure-immobilization technique. First place a 2-inch-square cloth pad about a quarter of an inch thick over the sting, then apply a firm elastic wrap directly over the padded sting site, extending at least four to six inches on either side of the wound. Take care to allow adequate circulation to the fingers and toes; there should be normal feeling and color. Splint the limb to prevent motion. If the sting is on the hand or arm, apply a sling as well.

In Australia, surf lifesavers (lifeguards) may carry antivenin, which is given as an intramuscular injection at the first-aid scene.

Second Steps and Aftercare for Treatment of All Stings: Apply soaks of vinegar or rubbing alcohol for 30 minutes or until pain is relieved. Baking soda powder or paste is recommended to detoxify the sting of certain sea nettles, such as the Chesapeake Bay sea nettle.

If these decontaminants are not available, apply soaks of dilute (quarter-strength) household ammonia. A paste made from unseasoned meat tenderizer or papaya fruit may be helpful; do not exceed 15 minutes of application time, particularly not upon the sensitive skin of small children. Meat tenderizer contains papain, and may also be quite useful to alleviate the sting from the thimble jellyfish that cause sea bather’s eruption. Do not apply any organic solvent, such as kerosene, turpentine, or gasoline.

After decontamination, apply a lather of shaving cream or soap and shave the affected area with a razor to remove the stingers. In a pinch, you can use a paste of sand or mud in seawater and a clamshell.

Reapply the vinegar- or rubbing alcohol-saturated compress for 15 minutes.

Apply a thin coating of hydrocortisone lotion (0.5 to 1 percent) twice a day until the redness disappears, but not for more than seven days. Anesthetic ointment (such as lidocaine hydrochloride 2.5 percent or a benzocaine-containing spray) may provide short-term pain relief.

If the victim has a large area involved (an entire arm or leg, face, or genitals), is very young or very old, or shows signs of generalized illness (nausea, vomiting, weakness, shortness of breath, chest pain, and the like), seek immediate help from a doctor. If a child has placed tentacle fragments in his mouth, have him swish and spit whatever potable liquid is available. If there is already swelling in the mouth (muffled voice, difficulty swallowing, enlarged tongue and lips), do not give anything by mouth, protect the airway and rapidly transport the victim to a hospital.

Dr. Paul Auerbach is clinical professor of surgery in the Division of Emergency Medicine at Stanford University and chief operating officer for MedAmerica in Oakland, Calif. A founder and past president of the Wilderness Medical Society, Auerbach serves as an adviser to the Divers Alert Network, National Ski Patrol System and Institute for Preventative Sports Medicine.

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