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Wim Hof, the Dutch extreme athlete known as the Iceman, was born in 1959 in Sittard, one of nine children. At 17 he felt a sudden urge to jump fully clothed into a freezing canal by Beatrix Park in Amsterdam. His first wife, the mother of his four children, was diagnosed with schizophrenia and died by suicide in 1995, and he found that freezing water was the only place his mind could escape the grief. The episode explains how cold shock triggers vasoconstriction and floods the brain with norepinephrine, pushing out rumination.

In March 2000 he tried a record under-ice swim without goggles, his corneas froze, and a rescue diver pulled him out unconscious; the next day he swam 57.5 meters for a Guinness record. In 2007 he ran a barefoot half marathon on snow and ice in Finland in 2 hours 16 minutes and climbed to 6,700 meters on Everest in shorts. A 2011 Radboud University study suggested he could influence his autonomic nervous system and immune response, and a 2024 meta-analysis of eight studies found possible reduced inflammation but samples of 15 to 48 people, over 86 percent male, and no blinding. His own researchers said his claims about cancer, multiple sclerosis and rheumatoid arthritis were unjustified.

• Using an Amsterdam fountain jet as an enema after the city raised water pressure perforated his bowel, and his trained pain tolerance delayed his emergency surgery.
• Hyperventilation lowers carbon dioxide and can lead to shallow water blackout; his company advises practicing only sitting or lying down, never in or near water.
• An expert cited in the episode said up to 63 percent of people who hold their breath before a cold plunge suffer an arrhythmia.
• As of March 2024 there were 32 reports of deaths allegedly linked to the method, and a $67 million suit over 17-year-old Madeline Rose Metzger’s drowning was dismissed in July 2024.
• A 2024 de Volkskrant investigation revealed a 2012 Dutch conviction for assaulting his then girlfriend’s 18-year-old son, with 40 hours of community service and a 350 euro fine.