The Science of Fire & Ice: Why Contrast Therapy Works
It’s not every day you find yourself standing in a snow cabin in your swimsuit, wondering how on earth this counts as relaxation. But that’s exactly where I ended up during a recent weekend at the Old Course Hotel in St Andrews — part of an experience that left me surprisingly energised and, dare I say it, calm. You can read more on that in my review:The Ultimate Retreat: Finding Balance in the Elements at the Old Course Hotel, but what lingered long after wasn’t just the chill of the snow or the heat of the sauna — it was how good I felt afterwards.
That feeling has a name: contrast therapy. Once the preserve of Nordic athletes, it’s fast becoming the next evolution of the cold-water craze. Across Scotland, outdoor saunas are popping up beside lochs and beaches, inviting us to alternate between fire and ice, heat and cold, stress and stillness. It sounds extreme, but the science behind it is solid — and few explain it better than Anna Deacon, wellness expert, cold-water advocate and author of Wild Fix Scotland (out September 2026, Bonnier Books).
Her upcoming book explores how nature restores and recalibrates us, and her deep dive into contrast therapy reveals how this rhythmic dance between hot and cold helps the body heal, strengthens resilience, and stills the mind.
What Is Contrast Therapy?
Sometimes called the “Nordic Cycle,” contrast therapy works by exposing the body to controlled extremes — heat (thermotherapy) and cold (cryotherapy). The hot phase causes your blood vessels to dilate, flooding muscles with oxygen and nutrients, while the cold phase makes them constrict, reducing inflammation and stimulating the nervous system.
Switching between the two acts like a natural pump for your circulation and lymphatic system — flushing out waste, improving recovery and promoting a deep sense of calm. It’s a process known as hormesis, where brief stress helps the body become more resilient over time.
When You Step Into the Heat
When you enter a sauna heated to around 70–100°C, your heart rate rises, your circulation increases and your body begins to sweat. This activates your sympathetic nervous system (your “fight or flight” mode), but in a way that’s controlled and beneficial.
That rush of heat mimics light exercise — strengthening the heart, promoting detoxification and easing muscle tension. It also triggers the release of endorphins and growth hormones, which boost mood and repair cells.
The benefits of sauna include:
Improved heart and brain health
Better sleep
Lowered HRV (Heart Rate Variability)
Enhanced immune function
Anti-inflammatory effects
Improved metabolic health
Reduced risk of respiratory illness
Improved mental wellbeing
Pain relief
No wonder the Finns have been doing it for centuries.
Then Comes the Cold
If the sauna is a warm embrace, the cold plunge is its sharp-tongued friend — brisk, invigorating and impossible to ignore. When you step into cold water, your skin’s receptors immediately signal to your brain that you’re in a stressful situation. Your heart rate and blood pressure spike, and hormones like adrenaline and cortisol are released in what’s known as a cold shock response.
The key, Anna explains, is to go slowly. Control your breath, let your body adjust, and within moments your parasympathetic nervous system — your “rest and digest” mode — takes over. That’s when the magic happens: dopamine levels can rise by up to 250%, oxytocin and serotonin are released, and the body shifts from panic to peace.
The benefits of cold-water exposure include:
Reduction in stress
Improved memory
Pain relief
Reduced inflammation
Improved symptoms of anxiety and depression
In short, it’s the ultimate natural mood-lifter — and a reset button for your nervous system.
How Long Should You Stay In?
There’s no one-size-fits-all formula. How long you spend in each phase depends on your body, your energy levels, and even the day. As Anna says, “You may feel different depending on how much sleep or food you’ve had, how well you’re feeling, and even where you are in your menstrual cycle.”
As a guide:
Sauna: 12–20 minutes
Cold: 1–3 minutes
But the real measure isn’t time — it’s how you feel. Tune in. Listen to your breath, your body and your instincts. You’ll know when you’ve had enough.
Why Contrast Therapy?
So why do we do it — willingly subjecting ourselves to extremes of temperature? The answer lies in balance. Cycling through hot and cold gives you the restorative benefits of both: circulation, healing, calmness and clarity. The heat opens the body up; the cold brings it back to centre.
As Anna Deacon puts it:
“Cycling through hot and cold gives us all the benefits from each type of therapy. And if you can do all of this in a beautiful setting in nature — feeling the air, the landscape, the grounding — then you’re really onto a good thing.”
It’s that combination — science meeting nature, body meeting breath — that makes contrast therapy so transformative. Whether you’re in a world-class spa or a wild loch, the principle is the same: fire, ice, and everything in between.