Reuters reports that according to a review of 19 studies published in the Annals of Emergency Medicine, the topical painkiller lidocaine and hot water appear to be the most effective remedies against stings by jellyfish in North America and in Hawaii.
For stings of the Portuguese man-of-war, vinegar may be useful, but will increase pain and cause further nematocyst (venom sack) discharge from the stings of other types of jellyfish.
No evidence was found for the efficacy of meat tenderizer and urine against jellyfish stings.
Finally, for onsite first aid, the study’s lead author suggested that beachgoers carefully remove nematocysts from the skin by using a credit card edge to scrape them off.
Sting victims should not use their bare hands to remove tentacles and should carefully wash the sting area with saltwater.