Climate change is increasing sea temperatures, leading to an uptick in number of jellyfish. Some of the most venomous jellyfish have even been spotted in US waters.
While most jellyfish stings are mild, delayed or recurrent reactions can occur, leading to prolonged inflammation. Other jellyfish stings can cause serious health concerns and even death.
There is no consensus on the best method of treating jellyfish stings, but expert researchers say that common remedies like urine or scraping the sting site are dangerous.
With global sea surface temperatures rising, people are seeing a sharp increase in the numbers of warm water–loving jellyfish. Many of your patients are probably spending time at the beach this summer—whether here or abroad—and some may be stung by jellyfish. 
There are thousands of species of jellyfish, all of which produce a different sting experience—from a mild electrical rush to a severely painful burn.
What happens when a jellyfish stings someone?
According to Dr. Angel A. Yanagihara, PhD, associate research professor at the University of Hawai’i at Mānoa’s Department of Tropical Medicine, Medical Microbiology and Pharmacology and School of Ocean and Earth Science and Technology, and the creator of the topical treatment "Sting No More," which can treat jellyfish stings.
“When a jellyfish stings, microscopic hollow tubules perforate the dermis to eject venom. These tubules are composed of cnidarian collagens and covered with a helical array of mineralized chitinous spines, which facilitate penetration of the venom.” She says that these are biochemically similar to crab shells. The injecting tubules reach one to two millimeters deep.
The sting itself is just the acute phase, Yanagihara explains. At that point, it’s “straight-up tissue damage. After that, if there are deeply penetrant tubules left in the body, ongoing inflammation may result.” The leftover remnants cause the recruitment and activation of many immune cells, including eosinophils, which are the body’s only way to rid the sting of the chitin. This is why jellyfish stings cause so much discomfort and itchiness.
Jellyfish sting reactions
Yanagihara says no one sting is alike; it all depends on the type of jellyfish, the body part affected (for example, if the skin was thin or thick), and how much venom was ejected.
It’s hard to know how many stings occur worldwide or how many lead to death, as they’re not always reported. Most stings are harmless. However, certain jellyfish stings can cause serious health concerns, sometimes resulting in serious immunological reactions, Guillain-Barré syndrome, anaphylaxis, and even death, depending on the type of jelly.
In the Philippines, an estimated 20 to 40 people die yearly from Cubozoa or box jellyfish stings. These jellyfish are generally considered the most venomous marine animal. The number of deaths resulting from box jellyfish stings is likely higher since “death certificates are not required in many countries within the range of box jellyfish,” according to the National Science Foundation. It’s worth noting that these stings affect many vacationing tourists as well as children.
Researchers also say that “More human lives have been lost from box jellyfish sting injuries than from shark attacks during the past 40 years.”
Some people stung by jellyfish experience Irukandji syndrome, a potentially fatal condition causing severe pain, muscle cramping, hypertension, and potentially life-threatening cardiac complications; it is frequently reported in Australia. Similar syndromes have also afflicted swimmers in places like Hawaii and Florida.
But even for swimmers who aren’t affected by fatal stings or serious syndromes, an encounter with a jellyfish sometimes leaves patients with a delayed or recurrent inflammatory reaction for weeks or even years. One rare case involved a patient dealing with “recurrent pruritic eruptions at the site of the sting over the course of 12 years.”
Less commonly, jellyfish stings can also cause type four hypersensitivity reaction, which Pediatric Dermatology says “manifests with delayed or recurrent cutaneous lesions at the primary site or distant from the primary site.”
Some stings can leave a rash for weeks or even months, leading, for example, to raised welts—long after the half-life of the venom, Yanagihara explains. This protracted inflammatory response occurs as the body tries to eliminate the foreign structures. Yanagihara says the sting can start a cytokine storm or continuous feedback loop of inflammation.
Certain patients may see a more intense reaction after a sting, Yanagihara says. For example, “It has been suggested that envenomations in patients with pre-existing autoimmune syndromes can trigger sting sequelae autoimmune response, complicating the story.” However, she says that this is just conjecture.
The reason for that conjecture?: “The problem is that there is very little biochemical work in this space,” Yanagihara says. “It’s a very small field.”
Treating jellyfish stings: A complex (and controversial) problem
If you run a quick search across various health websites—or if you peruse National Library of Medicine’s MEDLINE database—you’ll find hundreds of articles, studies, and treatment suggestions (including scraping stings with credit cards or covering sting rashes with urine, ice, or freshwater).
You’ll also find contradictory advice, some even coming from trusted medical publications. This is representative of the fact that jellyfish researchers do not agree on how venom affects the body or what the appropriate treatments might be. In fact, the “optimal treatment of stings remains controversial,” researchers write in International Maritime Health.
Dr. Christie Wilcox, PhD, who studied Cell and Molecular Biology with a specialization in Ecology, Evolution, and Conservation Biology at the University of Hawaiʻi at Mānoa, stated in an article published by the university that, “Even in the peer-reviewed literature, there are a lot of examples of recommendations that are made in passing in discussion sections without any direct evidence to back them up, and then those just keep getting repeated and cited over and over even though they’re not based on rigorous, empirical scientific evidence.”
The issue is widespread. For example, a survey of naval personnel published in the International Journal of Environmental Research and Public Health revealed that while 38% of respondents said jellyfish stings were a common wound in their units, 63% rated their own knowledge of jellyfish stings as “low” or “none.” The researchers suggested that “Medical education and training should be implemented to address this issue.” The same researchers suggested that jellyfish envenomation is a “serious public health issue and increases the burden on medical services.” Even lifeguards aren’t sure which methods to use on beachgoers who have sustained stings.
Jellyfish sting treatments to avoid
Yanagihara notes that many clinical textbooks contain outdated sting management suggestions. “Many well-meaning dermatologists are not aware of current research in this field and rely on outdated, ineffective, or even deleterious approaches,” she says.
So what can MDs do? For one, tell patients to skip the urine. “That episode of Friends has done more damage to this field than anything I can imagine,” Yanagihara says. “Historical first aid approaches by indigenous people never used urine. Traditional medicines may have used vinegar or a chewed-up poultice of a plant, but there’s no consensus on urine being useful. It's purely a fiction put up by Hollywood to get a few laughs.”
Additionally, she says that scraping the sting site with a credit card to remove the tentacles is problematic: “This particular trick was based on an old treatment for bee stings in order to remove their stinger. However, jellyfish capsules are microscopic. The jelly injects a tubule, which is left embedded in the tissue,” she explains. So when a patient uses a credit card, “All [they’re] doing is worsening things,” Yanagihara says. “There is no benefit, only harm—and it can be lethal in certain stings.”
Even though it may seem soothing, putting ice on a sting isn’t helpful, either. “Retrospective studies show that survival rates are decreased by use of ice and that outcomes are worsened by use of ice,” she adds.
Many dermatologists may recommend lidocaine or steroids, which Yanagihara says can help deaden pain transmission and reduce inflammation after the acute phase.
Here’s what patients should do for a jellyfish sting
It’s important to remember that there is no agreed-upon treatment method or single method for every type of jellyfish sting. However, “Data indicate that there are far better preclinical management approaches than are currently being used,” Yanagihara says. The first?: Vinegar is a good, easy place to start. Researchers reviewed its efficacy and found that it is a “primary first aid approach for box jellyfish envenomations,” and that it precludes the discharge of nematocysts, which the jellyfish fires to envenomate its victim.
Yanagihara says dousing the sting site in very hot water can inactivate the venom. One study has also shown that hot water immersion at 113 degrees Fahrenheit for 20 minutes for Portuguese Man-of-War stings is an effective and practical treatment for pain.
In the end, Yanagihara says researchers must deepen their understanding of jellyfish stings and encourages HCPS to explore updated literature.