Hot & Cold: The Science Behind Sauna and Cold Plunge

The Ancient Practice, Modern Science

The practice of alternating between extreme heat and cold has been central to Finnish sauna culture for centuries. Today, modern research is catching up to what Finns have known all along: the hot-cold contrast creates a cascade of physiological responses that benefit nearly every system in your body.

What Happens When You Go From Hot to Cold

In the Sauna (Heat Phase)

When you sit in a sauna at 170 to 200 degrees Fahrenheit, your body responds as if you are exercising:

• Your heart rate increases from a resting 60-80 beats per minute to 100-150 beats per minute
• Blood vessels dilate, improving circulation throughout your body
• Your core temperature rises by 1 to 2 degrees
• You begin sweating, losing up to a pint of fluid per session
• Your body releases endorphins and growth hormone

In the Cold Plunge (Cold Phase)

When you submerge in cold water (typically 38 to 50 degrees Fahrenheit), the opposite happens:

• Blood vessels rapidly constrict, driving blood toward your vital organs
• Your sympathetic nervous system activates, flooding your body with norepinephrine
• Your heart rate initially spikes, then slows as your body adapts
• Inflammation decreases throughout your body
• Your mind becomes intensely focused and alert

The Contrast Effect

It is the transition between these two states that creates the most powerful benefits. The rapid shift from vasodilation to vasoconstriction acts like a pump for your circulatory system, improving blood flow and flushing metabolic waste from your tissues.

Proven Benefits of Hot-Cold Contrast

Reduced Inflammation

Cold water immersion after sauna has been shown to reduce inflammatory markers in the blood. This is why athletes use the practice for recovery, and why it helps people with chronic pain conditions.

Improved Mood and Mental Clarity

The norepinephrine released during cold exposure can increase by 200 to 300 percent. This neurotransmitter plays a crucial role in focus, attention, and mood. Many people report feeling euphoric and mentally sharp after a hot-cold session, an effect that can last for hours.

Enhanced Immune Function

Research from the Thrombosis Research Institute found that regular cold water exposure increases white blood cell count. Combined with the immune-boosting effects of sauna, the hot-cold practice creates a robust defense against illness.

Better Sleep

The dramatic temperature changes help reset your body's thermoregulation system. Studies show that people who practice hot-cold contrast therapy report deeper, more restorative sleep.

Faster Recovery

Athletes from every sport use contrast therapy to recover faster between training sessions. The improved circulation speeds nutrient delivery to damaged muscles while removing waste products more efficiently.

How to Do It Safely

Start gradually. Your first cold plunge does not need to be an ice bath. Cool water is enough to trigger the contrast response. Build your tolerance over multiple sessions.

Time your rounds. A good starting protocol is 10 to 15 minutes in the sauna followed by 1 to 3 minutes in the cold plunge. Repeat two to four times.

Always end on cold. Finishing with the cold phase closes your pores, reduces inflammation, and leaves you feeling energized rather than drowsy.

Stay hydrated. The combination of sweating and cold exposure increases your body's demand for water. Drink between every round.

Listen to your body. If you feel dizzy, lightheaded, or unwell at any point, stop immediately and warm up gradually.

Our Cold Plunge Setup

Every MN Mobile Sauna rental includes a cold plunge tank alongside the sauna. We set it up right next to the sauna so you can step from heat to cold in seconds. In winter, the water is naturally cold. In summer, we add ice to bring the temperature down. Either way, the contrast is incredible.

The hot-cold practice is one of the most powerful tools available for improving your health, and it is also one of the most exhilarating experiences you can have. Once you try it, you will understand why Finns have been doing this for thousands of years.