Frostbite sets in, and in order to save the major organs, the body sacrifices blood flow to the extremities, cutting circulation from the fingers, toes, ears and nose to keep the blood flowing to the organs necessary for survival.
If not treated immediately, the damage to these extremities is irreversible. The other danger is hypothermia, an abnormally low body temperature.
At about 90 degrees, body functions start shutting down, and once that starts, you could be dead within minutes.
But Hof stayed in his tomb of ice for one hour and 12 minutes. Then, the ice was poured out of the tank, and Hof emerged, his skin still pink.
"He's not moving, he's not generating heat, he's not dressed for it, and he's immersed in ice water. And water will transmit heat 30 times faster than air. It literally sucks the life right out of you. And yet, despite all those negative factors, Wim Hof was very calm, very comfortable the entire time that he was immersed in that water," Kamler said.
It was a new entry for the Guinness World Records, but really, no one else out there seems able to compete with him. He just keeps breaking his own records.
At the hypothermia lab at the University of Minnesota in Duluth, scientists who've studied the cold for years say they've never seen anything like it.
Dr. Robert Pozos and Dr. Larry Wittmers, director of the lab, hooked up Hof to heart rate and core temperature monitors to evaluate his body's response after being submerged in an extremely cold water tank.
A normal response might include intense pain, cardiovascular stress and mounting hysteria, but with Hof, it's a much different story.
As he went into the tank, Dr. Wittmers explained, "What you're seeing basically is a situation in which the usual response to a shock or a cold was completely obliterated. There was no — none of the usual response you would see. And those responses that you see in most individuals that are exposed to that type of situation are uncontrollable."
From inside the tank, Hof said, "I feel the cold is a noble force, as they always say, and for me, right now, these readings are important but this is what I do every day in the winter, because I like it."
Since there's nothing abnormal about his body, all doctors can tell is that Hof's secret must lie in the wiring of his brain.
"It's very easy to speculate that the same mind control that you use to control your heart when you're scared also can be called upon to control the other organs in the body. And maybe that's how Wim Hof does this," said Kamler. "That's … it's speculation, but it sort of makes sense, and a lot of scientists are working very hard to try to figure this out now."
One answer might lie in an ancient Himalayan meditation called "Tummo," which is thought to generate heat. Hof began practicing the ritual years ago.
"Legends abound of practitioners of Tummo sitting out on the ice naked except for wet sheets that they have draped around them, and as they meditate, the sheets dry and the ice melts around them, even though it's freezing temperature," Kamler said.
If there's one ice-lover who has baffled scientists as much as Hof, it's American swimmer Lynne Cox.
At 15, Cox swam the English Channel in 14 hours, a Guinness World Record. She has also written two books about her adventures: "Grayson" and "Swimming to Antarctica."