Most people who use the sauna at Icelandic pools finish in the cold tub. Here is what happens in your body when you go straight from the heat into the cold, and what the research says about the combination.
The short answer
A cold plunge after the sauna cools you down much faster than standing in the air, reverses your circulation and wakes you up. As a result, the next sauna round is more comfortable. It is not needed to get the benefits of the sauna, though, and much of what is claimed about it is barely studied.
What happens when you go from the sauna into cold water
In the sauna your body temperature rises, the blood vessels in your skin widen, your heart beats faster and your blood pressure usually drops a little. Cold water reverses this within seconds.
You cool down fast and handle the next round better
In a 2026 British study, 16 adults did two 15-minute rounds in an 85°C sauna with a 10-minute break in between. When they spent 90 seconds in 20°C water during the break, which is much milder than most cold tubs, their core temperature at the end of the second round was half a degree lower (37.6°C instead of 38.0°C) and their heart rate was 108 beats per minute instead of 125. People found the second round more comfortable. This is the main reason to use cold water between rounds.
Your circulation reverses
The cold makes the blood vessels in your skin narrow, and blood moves to the core of your body. Your blood pressure, which dropped in the sauna, rises suddenly. In a Swiss study, systolic blood pressure rose in every participant when they got into 12°C water after the sauna. This sudden switch is what most people feel as the "kick".
You wake up
In the first seconds you get the cold shock response: you gasp, breathe fast and your heart jumps. Your body releases the stress hormone noradrenaline, which sharpens your attention. That is why people come out of the cold tub with more energy than they went in with.
Relaxation afterwards
In a Polish study, 30 young men did four rounds in a 90°C sauna with one minute in 10–11°C water after each round. The stress hormone cortisol fell from 13.6 to 9.7. There was no control group, so it is impossible to say whether it was the sauna, the cold water or both.
Do you need the cold tub to get the benefits of the sauna?
No. The large Finnish studies linking saunas to better heart health measured how often people used the sauna, not how they cooled off afterwards. Nothing suggests you miss out on the benefits of the sauna if you cool off in the shower or the open air instead. The cold tub is mainly a good way to cool down fast and enjoy more rounds.
How to do it
The sauna: 8–15 minutes, or until you are properly warm.
Rinse off the sweat in the shower before getting into the tub.
The cold tub: get in slowly, feet first, and breathe calmly for the first seconds. Start with 30 seconds to a minute. In a very cold tub you rarely need more than 2 minutes.
Rest for 5–10 minutes and let your body settle.
Repeat two or three times. Many people finish in the cold tub to leave feeling fresh, but if you want to relax before bed it may be better to finish in the hot tub.
Get out if you shiver a lot, feel dizzy or go numb.
What is claimed about cold water in general
Much of what is said about the cold tub comes from studies of cold water on its own, not after a sauna. A 2025 review of 11 randomised trials found this:
Weak evidence
Less stress
People reported less stress 12 hours after a cold plunge, but not right afterwards or the next day.
Weak evidence
Fewer sick days
In a Dutch study of more than 3,000 people, those who ended their shower with 30–90 seconds of cold water were 29% less often absent from work due to illness. They did not get sick less often, though, and people reported their sick days themselves.
Not supported
A stronger immune system
Inflammation markers in the blood rise temporarily after a cold plunge. No studies show that cold plunges strengthen the immune system in the long run.
Trying to build muscle?
Then skip cold water right after lifting. In a study where men sat in cold water for 10 minutes after every strength session for 12 weeks, they gained less muscle and strength than the others. This does not apply to an ordinary sauna visit at another time.
Who should be careful?
Going from heat to cold puts a strain on the heart, because your blood pressure goes from low to high within seconds.
If you have heart disease, an irregular heartbeat or high blood pressure, talk to a doctor before you start. In a study of people with stable heart failure everyone tolerated the sauna and cold water well, but they were supervised.
If you are pregnant, talk to a doctor or midwife first.
Avoid the sauna and cold water after drinking alcohol.
Never dive in or put your head under first, and do not swim in the sea alone. The cold shock response can make people inhale water.
Where to find a sauna and cold water
Here are a few places where you can go straight from the sauna to a cold tub or the sea:
Radtke T et al. Acute effects of Finnish sauna and cold-water immersion on haemodynamic variables and autonomic nervous system activity in patients with heart failure. European Journal of Preventive Cardiology, 2016. https://pubmed.ncbi.nlm.nih.gov/26152773/