Back in 1997 all the friends from that eponymous television show trekked to the beach, only to witness a jellyfish sting Monica. In this episode, Joey remembered seeing a documentary that advised urinating on the sting to ease the pain. Monica agreed to try the treatment and it worked. Unfortunately, in the real world treating a jellyfish sting by urinating on it may actually cause someone in Monica's situation even more pain, rather than relief. Urine can actually aggravate the jellyfish's stingers into releasing more venom. This cure is, indeed, fiction.

Jellyfish, those bulbous Medusa-like creatures, float near many of the world's beaches. Some of the jellyfish's skin cells are stinging cells, or cnidocytes. These specialized cells have organelles called nematocysts that contain venom. Cnidocytes are spread along the entire length of the jellyfish's tentacles.

These tentacles can be so long that swimmers might not see the jellyfish that stings them, but they will certainly feel it. "The pain is instant," says Joseph Burnett, a dermatologist at the University of Maryland Medical Center, who is part of the school's Consortium of Jellyfish Stings, which tracks jellyfish injuries worldwide. Once stung, angry, red, whiplike lash marks mar the skin. The pain radiates from the sting site and starts to itch, burn and throb as it blisters. Scratching it, though, can make the pain worse, because rubbing activates the nematocysts, which release more venom.

Jellyfish stings are painful, but they are rarely life-threatening. For most such injuries, in North America at least, the pain will not last longer than 24 hours, typically peaking five minutes after the sting occurs then dissipating over the next few hours. "[But] it depends on what jellyfish gets you," notes Christopher Holstege, a toxicologist and professor of emergency medicine at the University of Virginia.

Those 24 hours, though, could be uncomfortable without any treatment, which can be administered on the beach. Both Burnett and Holstege recommend washing the area with saltwater. Such rinsing will deactivate those pesky nematocysts that are still hanging on.

A freshwater rinse will have the opposite effect. Any change to the balance of solutes, such as the concentration of salts inside and outside of the cnidocyte, sets off stinging. Adding freshwater to the sting site dilutes the salts outside the cell, unbalancing the solutes. In reaction to this change, the nematocysts in the cells release more venom--and cause more pain.

But what about urine? It contains salts and electrolytes. "I can think of many other things I'd rather have on me," Holstege notes. The concentration of salts and other compounds people have in their urine changes, he explains. If it is too dilute it will be similar to freshwater and cause those stingers to fire.

Other liquids and compounds, however, can help. Most stings in North American waters can be assuaged by vinegar, or 5 percent acetic acid. For stings from a few species, Cyanea capillata and Chysaora quinquecirrha, a baking soda and seawater paste is even better.

Once rinsing deactivates all the nasty nematocysts, the attached bits of tentacle can be removed by coating them with shaving cream or a slurry of seawater and sand followed by shaving with a razor or even a credit card.

For pain, an oral analgesic should do the trick for North American jellyfish stings. Australia, though, has nastier jellyfish (such as the deadly Box Jellyfish) and most Australian lifeguard teams are equipped with morphine and antivenoms to treat unlucky swimmers Down Under.

Ultimately, time, not urine, is the best treatment for a jellyfish sting. "Urine is worthless," Burnett says.