If you are headed to the ocean for vacation, or live near it, you need to know about jellyfish: the potential for painful and sometimes dangerous stings, and what to do about them.

First off, avoid beaches that are not patrolled by lifeguards who know what is in the water. Beaches should be closed when there are high numbers of poisonous jellyfish in the water. Avoid swimming after major storms as well, because wave action may break up the tentacles so that they cannot be spotted, but they are still quite capable of delivering painful stings. Teach your children what jellyfish look like and warn them not to touch them under any circumstances (even the harmless ones).

As you are aware, jellyfish stings can produce a variety of unpleasant or dangerous effects. Local reactions to the stings can reoccur weeks to months later, and the reactions are not always limited to to the site of the sting. For example, eczematous skin reactions can occur far removed from the sting site. Angioedema (massive swelling) can occur at other locations as well, and can interfere with breathing.

The type of jellyfish sting can often be deduced by observing the pattern of the sting. Also, it is helpful to keep the tentacle removed from the skin, if possible, for identification of the jellyfish, should that become medically necessary. Removal hints are found below.

portuguese man-o-war (Physalia)

The portuguese man-o-war (Physalia) is so named because it sails along on the surface, driven by the wind like a sailing ship of old. Its powerful sting likewise reminds of the days when fighting ships ("men o' war") bristled with lethal cannon, as the jellyfish bristles with potentially lethal tentacles. Portuguese man-o-war tentacles contain cells that inject toxins

box jellyfish

The box jellyfish is native to waters off the northern coast of Australia and in parts of the Indo-Pacific. It can be lethal; there have been 55 confirmed deaths due to box jellyfish stings. Its toxin has several components:

  • dermatonecrotic toxin causes local skin and tissue destruction
  • hemolytic toxin causes massive breakdown of blood cells, which clogs the filtration mechanism of the kidneys, causing kidney failure
  • cardiotoxins can cause heart rhythm disturbances (arrhythmias)
  • neurotoxins cause paralysis and inability to breathe

Treatment of jellyfish stings

Stabilize vital signs
  • immobilize the affected body part
  • identify type of sting by pattern if possible
  • remove any tentacles and save stinger if possible for identification
Portuguese man-o-war
  • vinegar to remove tentacles
Sea nettles (found off the coasts of Virginia and the Carolinas)
  • slurry of baking soda to remove tentacles
Portuguese man-o-war, sea nettles
  • meat tenderizer (papain) breaks down the toxin proteins and neutralizes them
  • wash with sea water
  • do not use fresh water, alcohol, ammonia, or bleach - they can trigger release of more toxins
For local reactions
  • ice, pain medications, topical anesthetics such as benzocaine
  • cleanse ulcerated wounds several times a day and keep covered with antibiotic ointment
Other treatments
  • systemic antibiotics for wound infections
  • tetanus booster if status unknown or lapsed
  • corticosteroids and antihistamines for delayed eczema-type reactions
  • epinephrine (adrenaline) and systemic corticosteroids for sever reactions, shock

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