The Scandinavian winter swimming culture combines brief dips in cold water with hot sauna sessions—and now, a study of young men who participate regularly in these polar plunges finds that winter swimming may allow the body to adapt to extreme temperatures. The findings, publishing October 11 in the journal Cell Reports Medicine, suggest that routinely alternating swims or dips in chilly water with sauna sessions might affect how brown fat, also known as brown adipose tissue (BAT), burns energy and produces heat.