The chlorine added to water in swimming pools and the salt in seawater allow the water to remain liquid at sub-zero temperatures. Swimming in such water is significantly more challenging and dangerous. The experienced winter swimmer Lewis Gordon Pugh swam near the North Pole in water and suffered a frostbite injury in his fingers. It took him four months to regain sensation in his hands. Health benefits Although there are risks associated with the practice, scientific studies also provide some evidence for the following health benefits. When compared to a control group on the profile of mood states rating scale, winter swimmers experience less stress and fatigue and more vigor. They report to have a better memory function, better mood and feel more energetic, active and brisk. Swimmers who suffer from rheumatism, fibromyalgia or asthma report that winter swimming relieves pain. There are indications that winter swimmers do not contract diseases as often as the general population. The incidence of infectious diseases affecting the upper respiratory tract is 40% lower among winter swimmers when compared to a control group. Short term exposure of the whole body to cold water produces oxidative stress, which makes winter swimmers develop improved antioxidative protection. See also Apetor Ice bath Boxing Day Dip Cold water dousing Polar bear plunge Stunt swimming References External links Swimming Winter sports Open water swimming Bathing Winter swimming