A lot of people believe this old wives’ remedy, so first, it’s important to know where this pee-theory began. According to Science News, the legend of pee sterility began in the 1950s, when epidemiologist Edward Kass was trying to figure out a way to screen patients with UTIs before surgery. “Kass developed the midstream urine test (still used when you pee in a cup) and set a numerical cutoff for the number of bacteria in normal urine: not more than 100,000 colony-forming units (cell clusters on a culture dish) per milliliter of urine. A person tests ‘negative’ for bacteria in their urine as long as the number of bacteria that grow in a lab dish containing the urine falls below this threshold,” reported Science News.
Evann Hilt of Loyola University of Chicago explained to Science News that, because the level of bacteria didn’t meet Kass’s threshold, it was assumed that pee is sterile. Unfortunately, it’s not. According to the same report, Hilt and her colleagues used a more modern technique to detect low levels of bacteria in normal urine. “They put samples of the urine in lab dishes and let the urine bacteria grow under friendlier conditions. More than 70 percent of the urine samples contained bacteria, including at least 33 types of bacteria (at the genus level) in normal urine.”
Still, according to Bob Cooper, one of Australia’s top survival experts, the fact that urine isn’t 100 percent sterile doesn’t mean it can’t be used as a last resort for irrigating cuts and wounds. Just don’t let the pee-soaked wound fester in the sun: “Urine can get septic pretty quick after it comes out of the body,” he told ABC.
Tim Spicer, a nephrologist and the director of Renal Services at Southwest Sydney Local Health District, agrees that in the case of an emergency, urine can help flush your wound — but it’s not going to do much beyond that. “There’s no doubt that urine contains lots of substances [like ammonia]. … But none are proven in their effectiveness [when compared to] iodine or alcohol or any other substance we might use to clean a wound,” he explained in the same ABC article.
As for the injury most commonly associated with the pee cure — the jellyfish sting — it turns out, peeing on said sting can actually cause more pain than relief. Joseph Burnett, a dermatologist at the University of Maryland Medical Center, and Christopher Holstege, a toxicologist and professor of emergency medicine at the University of Virginia, told Scientific American that the best thing to do in the case of a jellyfish sting is to rinse the area in saltwater, which deactivates the nematocysts (aka, the jellyfish’s stinging mechanism).
Peeing on the sting, meanwhile, can have a similar effect to using freshwater, which may cause the nematocysts to release more venom and cause more pain. “‘The concentration of salts and other compounds people have in their urine changes,’ [Holstege] explains. If it is too dilute it will be similar to freshwater and cause those stingers to fire,” Ciara Curtin reported in the same article for Scientific American.
All in all, the the truth is that if someone offers to pee on your body to help you out, they’re just, well, taking the p*** and nothing more.