Here's what to do immediately if you get stung by a jellyfish

Q:  I got stung by a jellyfish a week ago and it seemed better, but the area now has hives and is super itchy. What can I do?

A:  Several of the over 200 types (and 10,000 species) of jellyfish-like creatures can be found in every ocean. There are many differences between these gelatinous creatures, but in this overview I will concentrate on the similarities and take some liberties making generalizations.

Jellyfish are 90 percent water (people are about 67 percent), and are typically translucent - hard to see, but not invisible. They have an umbrella-like structure (where the mouth and digestive system are), and tentacles that hang down from it. The size of the umbrella varies quite a bit, from less than an inch to several feet or more. The tentacles can be inches long but, in some species, can be over 100 feet.

The Portuguese-man-of-war is recognized by its balloon-like float, which may be blue, violet or pink and rises up to 6 inches above the water line.
The Portuguese-man-of-war is recognized by its balloon-like float, which may be blue, violet or pink and rises up to 6 inches above the water line.

Jellyfish are hunters.  Some just float along, possibly hitching a ride on seaweed, and some propel themselves (the fastest swims about 10 feet a minute). Clearly even these "swimmers" cannot overtake their prey with speed; instead they are "passive" hunters, utilizing their tentacles (which are covered with toxin-filled sacs called nematocysts) to kill. A jellyfish senses mechanical and/or chemical stimulation when unsuspecting prey wanders too close, and then uncoils small skin-piercing, needle-like organelles that inject toxin. Jellyfish cannot hold their catch if it fights back, so their toxin must be fast acting.

Worldwide, over 150 million people are stung by one of the 10,000 species of jellyfish-like creatures each year. Avoiding being stung is always a good idea, so check with the local lifeguard regarding swimming conditions, and never swim alone so you have a buddy in case something happens.

Atlantic sea nettle jellyfish deliver a painful sting.
Atlantic sea nettle jellyfish deliver a painful sting.

Most jellyfish stings cause no/minimal symptoms or an immediate stinging pain. A percentage of these are followed by red, hive-like lesions that develop within minutes to a few hours. In some cases these lesions may become painful, throbbing and/or itchy.

However, about 100 species of jellyfish have toxin that is dangerous to humans, causing systemic reactions. For example, a Portuguese-man-of-war sting may cause painful hives and skin irritation, and there have been human deaths from it. The box jellyfish sting may just cause severe pain and has been implicated in human deaths. The Irukandji jellyfish sting may cause “Irukandji syndrome” (back/muscle pain/cramps, burning skin sensations, headache, nausea, vomiting, sweating, increased heart rate, increased blood pressure, extreme anxiety, and/or fluid buildup in the lungs) and can be lethal to humans. These types of jellyfish are usually encountered in the Indo-Pacific areas, especially around Northern Australia.

Lions mane jellyfish in Green Harbor, Marshfield on Monday June 22, 2021 Greg Derr/The Patriot Ledger
Lions mane jellyfish in Green Harbor, Marshfield on Monday June 22, 2021 Greg Derr/The Patriot Ledger

Treatment for jellyfish stings should be initiated as soon as possible. Seek immediate first aid; beach lifeguards are typically trained to administer this, especially if the local waters are known to have jellyfish species that may cause severe systemic reactions:

  • Life threatening complications should be emergently treated with basic life support measures, anaphylaxis should be treated, and the patient taken to an ER.

  • People with severe reactions may need to be hospitalized.  Aggressive supportive care and treatment for severe allergic reactions may be needed, and there is anti-venom for box jellyfish stings.

  • Suspected box and possibly Irukandji jellyfish stings should be treated with vinegar to prevent toxin release from any remaining nematocysts (suspected Man-of-war nematocysts may release toxin from vinegar treatment, so it is no longer recommended for their sting).

  • Remaining nematocysts from any sting should be removed (plucked out, with the rescuer being careful so they don’t get stung).

  • The sting area should be rinsed with sea water, but NOT rubbed, to minimize further toxin injection.

  • Symptomatic treatment such as antihistamines for itch, pain medications (immersion in very warm water about 104 to 122 degrees Fahrenheit may help minimize the pain for some stings) and/or local treatments such as ice packs, can be utilized.

  • For the subset of people who develop itchy (sometimes very severe), hive-like lesions a week or two later, treatment options include antihistamines and/or topical hydrocortisone cream (and if these are not sufficient medical evaluation should be obtained).

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.

This article originally appeared on MetroWest Daily News: Jellyfish stings call for immediate first aid, lifeguards are trained