It turns out that the practice of splashing cold water on your face to refresh yourself actually prompts a physical change. Immediately upon facial contact with cold water, the human heart rate slows by 10 to 25 percent. The phenomenon is called the diving reflex, and it’s the body’s physiological response to submersion in cold water.
The mammalian diving reflex takes over in an emergency, shutting down the body’s systems so it can conserve energy -- and survive. The diving reflex is why it may be possible to revive an accident victim after an extended period in icy water: Slowing the heart rate lessens the need for bloodstream oxygen, leaving more for other organs.
Survival mechanism for all mammals:
- In addition to a slower heart rate, the reflex causes the capillaries in the skin and limbs to constrict, redirecting blood away from the body’s surface and toward vital organs.
- The diving reflex also seems to fortify the torso against the crushing effects of water pressure. It also helps preserve the body’s core temperature.
- All mammals have the diving reflex. Seals, for example, use it to withstand the pressures associated with diving for food. A seal's heart rate can go from 125 beats per minute to as few as 10 beats per minute.