The study concentrated on remedies for the painful stings of the Portuguese man o’war (Physalia physalis, strictly speaking a siphonophore rather than a jellyfish) and its Pacific counterpart the bluebottle (Physalia untriculus). Until now it has been recommended not to use vinegar to treat the Physalia stings.

The study was prompted by last year’s influx of Portuguese man o’war along France’s Atlantic coast. Like other cnidarians (jellyfish, corals, anemones and hydrae) their tentacles carry tiny capsules called cnidae that can discharge venom into a victim.

When the tentacles touch a victim, only a small proportion of the cnidae are discharged immediately, but if not removed they can go on firing their venom for two weeks or more.

The research involved testing a variety of rinse solutions to see if they caused the cnidae to discharge their venom. Any that did not cause immediate significant discharge were investigated further to see if they might actually inhibit such discharge.

Undiluted vinegar, the main constituent of which is acetic acid, was shown to prevent further discharge and to allow safe removal of tentacles and cnidae. Any dilution reduced these protective effects. If the affected area was afterwards immersed in 45 degree C water, or a heatpack applied, fewer of the red-blood cells used in the tests were killed by the venom.

Ineffective treatments included scraping away the tentacles, because the increased pressure caused the cnidae to discharge. Rinsing with seawater simply spread the cnidae over a wider area, and ice-packs made them more likely to discharge.

Commonly recommended treatments including urine, alcohol, baking soda, shaving cream, soap, lemon juice, alcohol and cola all caused varying amounts of immediate discharge and failed to inhibit further discharge - so were likely to worsen the stings. 

The study was a collaboration between two scientists from the University of Hawaii at Manoa, which has carried out previous research on box jellyfish, and two from the National University of Ireland Galway. They plan to continue their research using the lion’s mane jellyfish.

Their paper is published by MDPI here

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