You've probably seen videos of Matt Lauer, Martha Stewart, Justin Timberlake, Ethel Kennedy and your Facebook buddies taking the Ice Bucket Challenge.
In terms of a fundraiser, it's clearly successful: it's helped raise $2.3 million for the ALS Association since July 29.
But do the benefits of cold water dousing extend beyond the ability to make videos go viral? Health claims of cold showers, ice baths, and Finnish saunas (i.e., jumping into frozen lakes) range from improved circulation to speeding up your metabolism.
While studies on the subject have been "all over the place," according to Michael Bergeron, a professor of pediatrics at Sanford School of Medicine of the University of South Dakota, exposure to the cold water would likely have to be at least 10 minutes to have any chance of impacting your body.
"So when people think they're doing marathoners a big favor by spraying them with their garden hoses, it actually does nothing to cool them -- although it may feel good," Bergeron said.
In fact, such a quick exposure could lead to body signals getting mixed up, he said. When cool water splashes a highly sensitive area like your face with lots of nerve endings, you may not sense that you're overheating.
Longer exposures, though, may be beneficial in certain situations: For exertional heat stroke, for example, the best way to quickly lower body temperature is to submerge yourself in cold water -- up to the neck -- for at least 10-15 minutes, he said. There's also evidence that it prevents delayed onset muscle soreness, probably because changing the muscle temperature lessens the damage of overheated cells in the muscle.
Some health and fitness gurus say cold water can improve blood circulation. Depending on the application method, that could be true -- at least temporarily, said Thomas Swensen, professor and chair in the Department of Exercise and Sport Sciences at Ithaca College.
"What they're talking about is reactive hyperemia," he said. "Think about when you were little and came inside after being in the snow all day long. You took a hot shower and it felt like your toes swelled up. That was the circulation returning." In order to reduce inflammation, then, repeated applications of ice water would be necessary.
An even more recent trend, alternating cold with heat, is "even more sketchy" in terms of research, Bergeron said.
"It may feel good, but there's no evidence to show it helps you perform better or that it enhances recovery," he said.
Assuming that some benefits of cold water therapy exist, there is some good news: Research from Stanford shows that full-body submersion (i.e., jumping in an ice-cold tub up to your neck) may not be necessary to lower body temperature. The researchers developed a prototype of an ice glove that cools the body through the palm, where networks of veins devoted to rapid temperature management are concentrated.
Since none of these therapies are likely to cause any harm (with the possible exception of cardiovascular patients), experts said, there's no reason not to try them.
"You can argue the perceptual effect: If you think it's helping, it probably is," Bergeron said. "If it motivates you or gets you pumped up, it can certainly enhance performance. But physiologically, it's unlikely."
In other words, there's no physiological excuse not to dump a bucket of ice over your head.