Cold exposure

Cold exposure is the deliberate use of cold air, water, or ice (cold showers, ice baths, cryotherapy) as a hormetic stressor. Acute cold triggers noradrenaline release and peripheral vasoconstriction and, if sufficiently intense, shivering thermogenesis; some protocols are non-shivering by design. It may activate brown adipose tissue, though BAT activation in humans varies substantially with the exposure protocol and detection method. Reported effects include improved cold tolerance and subjective alertness; evidence for metabolic, immune, and longevity benefits in humans remains limited and mixed.