The Science of Ice Baths: What Happens to Your Body During a Cold Plunge
In recent years, ice baths and cold plunging have surged in popularity, with enthusiasts claiming everything from boosted mood to better metabolic health. A compelling WIRED video explores exactly what occurs physiologically when someone steps into freezing water. Cold plunge practitioner Josh Cameron demonstrates the process in real time, while metabolic scientist Dr. Susanna Søberg, PhD, explains the body’s reactions step by step.
Dr. Søberg, founder of the Søberg Institute and author of the bestselling book Winter Swimming, specializes in how deliberate cold (and heat) exposure can optimize health. She guides viewers through the immediate shock, the internal changes, and the potential longer-term benefits backed by research.
The Initial Cold Shock Response
As soon as the body enters ice-cold water, a powerful “cold shock” kicks in. Breathing becomes rapid and shallow — a form of hyperventilation — as the nervous system activates the fight-or-flight response. This is the body’s way of dealing with sudden stress.
Blood vessels in the extremities constrict sharply to redirect warm blood toward vital organs and protect the core. At the same time, levels of norepinephrine (a key stress hormone and neurotransmitter) can surge up to 2.5 times above baseline. This chemical rush helps regulate body temperature and prepares the body for action.
Brown fat — a special type of fat that burns calories to generate heat — also gets activated by norepinephrine. Unlike regular white fat, brown fat uses glucose and stored fat as fuel, which may support metabolism and play a role in preventing lifestyle diseases such as type 2 diabetes.
Shivering and Muscle Response
As the plunge continues, muscles begin to shiver, particularly in the chest (pectoralis major) and thighs. Shivering is the body’s attempt to produce heat through rapid muscle contractions. According to Dr. Søberg, noticeable shivering in these areas often signals that it’s a good time to exit the water for optimal benefits, rather than pushing for extreme durations.
Even partial immersion can have effects. Submerging up to the neck causes significant heat loss, and including the head increases it further. Interestingly, exposing just the hands or other small areas can still trigger systemic responses, as seen in people historically adapted to cold work like fishermen.
The Neurochemical Boost
One of the most discussed perks of cold plunging is its impact on brain chemistry. Cold exposure triggers a significant release of dopamine — the “motivation and reward” molecule — which can remain elevated for hours afterward. This surge is sometimes compared in intensity to certain stimulants, though through a natural pathway, and many people report improved mood, focus, and resilience.
Other neurotransmitters and hormones also rise, including serotonin (linked to emotional balance and vagus nerve tone) and oxytocin (often called the “love” or “bonding” hormone). These changes contribute to the sense of calm, euphoria, or emotional warmth that frequently follows a plunge.
What Happens After Getting Out: The Afterdrop
Exiting the ice bath doesn’t mean the effects stop. As blood vessels dilate again, cooler blood from the core circulates to the extremities, often causing more shivering and a temporary drop in body temperature known as the “afterdrop.” This phase is normal.
Dr. Søberg emphasizes the Søberg Principle: allow the body to rewarm naturally without jumping straight into a hot shower or sauna right away. Forcing the body to generate its own heat (through movement and shivering) can further activate brown fat and enhance metabolic benefits.
Long-Term Benefits and Practical Tips
With regular practice, cold exposure may improve the body’s overall temperature regulation, enhance insulin sensitivity, and support faster glucose clearance from the blood. Studies on winter swimmers and controlled cold protocols suggest these adaptations can help build resilience against stress and metabolic challenges.
Dr. Søberg’s research points to a minimum effective dose: roughly 11 minutes of cold exposure per week, spread across 2–3 sessions. Sessions don’t need to be extremely long or painfully cold — consistency matters more than intensity for most people.
She also notes that combining cold with heat exposure (such as sauna sessions) can amplify benefits, including better cardiovascular responses and overall stress adaptation. However, cold plunging isn’t suitable for everyone. People with heart conditions or certain health issues should consult a doctor before trying it.
A Balanced View
Cold plunging taps into ancient practices seen in various cultures, from Egyptian hygiene rituals to Greek ideas about balancing bodily fluids. Modern science has built on this with studies on hypothermia, brown fat thermogenesis, and metabolic health.
While the video showcases dramatic real-time changes and promising benefits, experts stress that results vary by individual. The practice offers a form of “hormetic” stress — a controlled challenge that may strengthen the body and mind over time — but it’s not a miracle cure.
Whether you’re curious about trying your first cold shower or already a regular plunger, understanding the science helps set realistic expectations. As Dr. Søberg explains, the discomfort in the moment can translate into meaningful physiological adaptations that support long-term well-being.
Have you experienced the effects of cold exposure firsthand? The growing body of research suggests it may be worth exploring safely and mindfully.
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