The swimmer comes out of the water with a red stripe on his arm, a finger wide, and already a circle forms around him. Somebody has vinegar ready and somebody swears by ammonia, there is always one who suggests peeing on it, and the lifeguard pushes through with the ice. For many years, when the circle reached me, I said alcohol, and I had a reason. But in that circle, myself included, there was no one who had ever watched a nematocyst under a microscope while something was poured over it. It has been done, and I went to read.

In our waters the jellyfish is nearly always Pelagia noctiluca, the mauve stinger, purple, with a bell of four to ten centimetres, the commonest and most venomous in the Mediterranean. In Salento, in the heel of Italy, where the stings have been counted at the summer beach clinics, they are the main thing that brings people in. On its tentacles and oral arms it carries millions of nematocysts, collagen capsules a hundredth of a millimetre across, holding a coiled thread and a liquid at a pressure that in Hydra, where it has been measured, reaches a hundred and fifty atmospheres. When the capsule opens water rushes in, the pressure fires the thread like a harpoon and the venom passes into the skin; the first jolt lasts less than a millionth of a second. The capsules that have already burst have already injected, and for those only the pain is left to treat. The ones still shut, on the bits of tentacle left on the skin, are the problem, and whatever is poured on the sting is there to keep them shut while they are taken off.

My reason was osmosis. Discharge is water entering the capsule and bursting it; fresh water, more dilute than the sea, drives it in, which is why it is not to be used. Alcohol, I thought, does the opposite, draws water out, and on top of that evaporates and cools. By the same reasoning I could have recommended salt, the simplest hypertonic solution there is.
In Messina, where Pelagia drifts in swarms through the Strait, Antonio Salleo and Giuseppina La Spada have studied its capsules since the 1980s. In 1984, on isolated capsules, they found that what opens them is anions, chloride and iodide, while calcium, barium and magnesium keep them shut. Salt fell there, because salt is chloride. In 2014 their group, with Rossana Morabito, tested 1 per cent lidocaine, 70 per cent alcohol, 20 per cent ammonia and 5 per cent acetic acid on the oral arms, sensitising the capsules with sugars and amino acids and then touching them with a probe. On their own, none of the four opened the capsules; all four sharply cut the discharge set off by the stimuli. The authors conclude that immediate treatment, even with alcohol or vinegar, may reduce the lesions.

I had been right.
For as long as it took to open the Barcelona papers. Ainara Ballesteros and Josep-Maria Gili, at the Institute of Marine Sciences, did something simpler and closer to the beach. A piece of tentacle in the liquid, and five minutes under the microscope, with no sensitising and no touching. In 2021 vinegar on its own set off the nematocysts of Pelagia, all four types, a medium discharge; in the venom-through-a-membrane test vinegar and seawater did not differ, so vinegar neither reduced the venom nor measurably added to it. On the box jellyfish Carybdea marsupialis, which lives in the same seas, vinegar blocked them instead, which is why the same advice can be right for one jellyfish and wrong for the one beside it. To make the Carybdea capsules fire and show that vinegar kept them shut, the stimulus chosen was 96 per cent alcohol, which opens them wholesale. The year after the test widened to thirty-one substances, more or less everything to be found in a bag or a kitchen. Seawater leaves the capsules as they are. Almost everything else opens them, ammonia, bleach, lemon, cola, baking soda, table salt. Fresh water does not open them, but loosens the stinging cells from the tentacle, which roll over the skin and go off on contact, and it stays out for that. Alcohol on its own was not tested; 10 per cent lidocaine dissolved in alcohol is one of only three things that keep the capsules shut even under stimulus, and the over-the-counter lidocaine gels appear in neither paper. On other jellyfish plain alcohol has an ugly record. On the American Chrysaora, in 2010, it opened the capsules; on the Korean Nemopilema, in 2016, people who tried it on their skin felt worse than before.

The disagreement between Messina and Barcelona is over vinegar and ammonia, and the Spaniards put it down to method. Who pays should be added. The Barcelona papers are funded by ISDIN, a cosmetics company. In 2022 the four authors, Ballesteros and Gili included, declare that they have applied for two patents and that ISDIN took part in the analysis and reviewed the text; in 2021, same funder and one co-author from the company, one reads "no conflict of interest". The photographs remain what they are, but the reader should know before buying the cream. As for the aluminium chloride gel that every Italian hospital recommends, it has never been tested on Pelagia. Its Australian cousin, Stingose, aluminium sulphate in a detergent, blocked discharge in an American study of 1983 on Chrysaora; I cite it from the Barcelona table, without having read the original.

On alcohol I was right for the half that can be measured, the Messina half, where it does not open the capsules and holds back discharge. I was wrong about why, because the capsule gives up no water outward and alcohol crosses membranes rather than pulling on them. And it is the half not yet measured on Pelagia, alcohol on its own without sensitising, that makes me change my advice, because elsewhere it has opened capsules and because something exists that does the same job without the doubt. On the pain the Australians, who know more about jellyfish than anyone, rewrote their guidelines last year, and say that outside the tropics you go with heat or cold, and the evidence is in conflict. Heat and cold work on the venom already inside, not on the capsules, and they come afterwards.

So today, when the circle reaches me, I say get out of the water and rinse with seawater. Take the fragments off with the edge of a card drawn gently, without rubbing, without sand and without fingers. Leave the vinegar, the ammonia, the urine, the salt and my old alcohol in the bag. Put the cold on afterwards, rested and never pressed, best of all the arm in a bucket of cold seawater, because an ice cube on the skin melts into fresh water and presses; or hot water, if there is any at a temperature the skin can take, as the Australians prefer for their Physalia. I must say, because it is the objection I raise against others, that Yanagihara and Wilcox in 2017 found on box jellyfish that rinsing with seawater, scraping and ice increase the venom injected; that is not Pelagia, but the finding exists. If the pharmacy has a lidocaine gel, it is the one thing on which Messina and Barcelona shake hands. You see a doctor if the reaction spreads beyond the stripe, if breathing is difficult, if an eye is hit, if the sting is on a small child.

The circle around the swimmer can break up. What he needs he already has around him, the sea and a card in his pocket. The alcohol I have put back in the cabinet.



References
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