The belief that swimming in cold water can improve one's health is hardly new. For centuries, people from all over the world have reported that immersing themselves in cold water alleviates their pain and improves their overall well-being. Even Katharine Hepburn famously claimed to treat her winter colds by swimming in the icy waters of the Pacific Ocean. But until now, the practice has been treated lightly by the scientific community, the curative effects all but dismissed by doctors seeking medicine-centered solutions for their patients' illnesses.