The popularity of cold-water exposure has outpaced research into the subject.
Of all the possible benefits of cold exposure, soothing sore muscles may be backed with the most evidence.
“There have been a couple of studies showing that there may be some decreased soreness after people were immersed in cold water for about 10 minutes versus those who did not do any cold therapy,” Dr. Zaslow says. "When you're in cold water, your blood vessels constrict so there's less blood flow to the area, then there's less swelling and inflammation leading to less pain."
Many people claim that cold exposure helps boost moods, but this hasn't been proven.
"The study that showed it might be helpful for mental health looked at people who took a course in swimming in cold seawater," Dr. Zaslow says. "But exercise can improve your mood and wellbeing. To me, it's a soft case that it was the cold water providing the aid."
The same is true of longevity claims. (Picture older men who assert that their morning swim in a cold lake helped them reach their 80s.)
"I haven't studied these claims, but I say it was the swimming," Dr. Zaslow says. "I don't know if the temperature of the water matters. Physical activity has been shown to extend lifespan, so it's hard for me to say if it's physical activity versus the cold."
Some people practice cold exposure to boost the immune system, but the research isn't definitive.
"The idea would be that the cold water is stimulating your immune system," Dr. Zaslow says. "If a decrease in cold or other viral illnesses is noted, it could be the cold-water immersion, but most likely, there are many factors that contribute."