(Reuters) - There's a lot of folk remedies for treating a jellyfish sting, but science suggests that hot water and topical painkillers actually work the best - at least in North American waters.

Popularly promoted remedies range from vinegar to meat tenderizer to baking soda mixed with water. In a pinch, the victim - or a very good friend - might try urinating on the sting.

Current research demonstrates variable response to treatment, often with conflicting results according to species studied, which contributes to considerable confusion about what treatment is warranted, wrote Nicholas Ward, at the University of California, San Diego, in the Annals of Emergency Medicine.

Though the American Heart Association and American Red Cross currently recommend using vinegar or a baking soda slurry, followed by heat or ice, those remedies are based mainly on studies done in Australia and Indonesia, he added in an email to Reuters Health.

The jellyfish species there aren't commonly found in North American waters, so Ward said he and his colleagues studied medical literature for studies specific to North American and Hawaiian jellyfish, and found 19.

Based on those studies, it seems the most broadly effective remedies are simple hot water and creams containing the pain-numbing medication lidocaine.

The principle behind the use of lidocaine is that it acts as a local anesthetic (and) appears to inhibit the further discharge of nematocysts remaining on the skin, Ward said.

Nematocysts are the venom sacs jellyfish leave behind as a further insult after they sting. It's important to get those off the skin, because they can continue to release venom.

Simple hot water might help by denaturing and inactivating the venom, Ward said. But hot water might not be available at the beach, and not everybody carries lidocaine with them.

In that case, removing the venom sacs from the skin and washing the are with saltwater might help, though the sacs must be handled with care. The edge of a credit card, or something similar, might work well.

The idea is to avoid crushing the sac and spreading venom, which wiping off with a towel could do, he said.

Vinegar does help with some species, such as bluebottles or Portuguese man-of-wars, which are mainly found off the coast of Florida and in the Gulf of Mexico.

But vinegar may actually worsen the pain of stings from most North American jellyfish, as well as causing any remaining venom sacs to discharge, Ward said.

Hot water and lidocaine appear more widely beneficial, he wrote. bit.ly/L4TVrx (Reporting from New York by Amy Norton at Reuters Health; editing by Elaine Lies)