Post-Plunge Rewarming: Why Warming Up Naturally is Better Than a Hot Shower (Avoiding Afterdrop and Maximizing Benefits)

The choice of rewarming protocol—whether you use external heat (like a hot shower or sauna) or allow your body to warm up naturally—directly impacts the physiological goals of cold exposure, particularly metabolic and brown fat activation.

The Søberg Principle

The core principle regarding post-plunge warming is referred to as the Søberg principle: if your goal is to increase metabolism (thermogenesis) through deliberate cold exposure, you want to force yourself to reheat on your own after the cold exposure.

• This means you should end with cold and not go from the cold shower or plunge directly to a hot shower or sauna.
• Ending on cold triggers a thermogenic metabolic response, where your body must expend energy to raise its core temperature back to baseline.

The Afterdrop Phenomenon

Rewarming naturally is tied to avoiding or managing the afterdrop, a phenomenon where your core body temperature continues to decrease after you get out of the cold water.

• During the Plunge: Blood vessels in your periphery (extremities) constrict (vasoconstriction) to shunt blood to your core to protect vital organs.
• After Exiting: As your periphery warms slightly, those constricted blood vessels begin to relax and open up (vasodilation).
• The Drop: Cooler blood from the surface flows back into the core, causing a temporary decrease in core body temperature.
• The Benefit: This afterdrop is what often induces shivering. Shivering is beneficial because it stimulates the production of brown fat and increases your metabolism, helping the body warm up again.

By taking a hot shower immediately after, you are short-circuiting or diminishing these metabolic increases that would otherwise be achieved by self-reheating.

The main concern is safety and the need for immediate warmth due to the physical discomfort of the "afterdrop," which can lead to intense shivering that interferes with daily activities.

• Risk of Afterdrop: The decrease in core temperature that occurs after exiting the cold can cause shivering. One individual shared a story of experiencing "crazy after drop" after a 15-minute plunge, leading to shaking so severe they "couldn't drive back home".
• Vulnerability: If you happen to get wet or extremely cold, to the point of getting frostbitten, you should not rub frozen hands or feet, and should not warm up freezing body parts if you know you can't keep them defrosted, as refreezing will worsen tissue damage. Defrosting should be done slowly and preferably with professional help using lukewarm water, not hot water, which can burn the skin.
• Loss of Control: Shivering feels like a "loss of bodily control," which many people avoid. However, sources advise that you should not be afraid of shivering, provided you are not getting hypothermic.

To maximize the metabolic benefits (brown fat activation and calorie burning) and promote resilience, always end your cold exposure session on cold and allow your body to warm up naturally.

If recovery from muscle soreness is your goal, cold exposure after training is beneficial and better than passive recovery. However, if your goal is to maximize muscle size (hypertrophy), wait four hours or more to do any cold exposure.

After exiting the cold water, do not immediately use a towel or step into a warm shower. Instead, allow your body to air-dry or dress warmly and move around slightly to let your body generate its own heat, maximizing brown fat activation and metabolic benefits.

Mistake: Taking a hot shower immediately post-plunge.
Fix: Always end on cold to maintain thermogenic benefits.

Mistake: Applying external heat to freeze-damaged skin.
Fix: Use lukewarm water for gradual defrosting or seek professional care.

Mistake: Ignoring the afterdrop.
Fix: Have a plan to reach a warm environment safely after your plunge.

Mistake: Huddling or drying off immediately.
Fix: Allow evaporation and mild shivering for maximal brown fat activation.

The crucial component for maximizing the metabolic and brown fat-activating effects of cold exposure is the rewarming process. By adhering to the Søberg principle—ending on cold and allowing your body to self-heat—you trigger natural thermogenesis, extending the calorie-burning and adaptation benefits. While a hot shower may feel immediately better, it sacrifices these key physiological effects. Always have a safety plan to manage the afterdrop—it’s a sign your body is working to warm itself up.