Step on the scales after a long sauna session and the number will probably have dropped. It's tempting to think the heat has melted something away. It hasn't, and understanding why makes it much easier to use a sauna well.
This guide answers the question properly: what that drop on the scales actually is, how many calories a sauna really burns, what the research says about saunas and weight, and the ways a regular sauna habit can genuinely help if you're trying to get healthier.
The short answer: it's water
In a hot sauna your body's main way of cooling down is sweating, and you can lose half a litre or more of sweat in a session without really noticing. A litre of water weighs a kilo, so it's easy to come out a few hundred grams to a kilo lighter.
That loss is water, not fat. As soon as you drink, and you should drink, it comes straight back. If the number on the scales stays down, it simply means you're still a bit dehydrated.
How many calories does a sauna burn?
Some, but not many. When you sit in the heat, your heart rate climbs and your body works harder to shed heat, so you do use a little more energy than you would sitting still at room temperature. A 2022 study that measured young men during a 10-minute sauna session found energy expenditure and heart rate went up, more so in men carrying more body fat, and that the changes stayed within safe limits.
The catch is that you're sitting down. Any extra energy you use is small compared with a walk, a swim or a cycle, and it isn't fat-burning in any meaningful sense. You'll see big calorie figures quoted online for a sauna session. Treat them with a lot of suspicion.
| What happens | Does it mean weight loss? | |
|---|---|---|
| Sweating | You lose water through your skin | Temporary. It returns when you drink |
| Heart rate | Rises, a bit like light exercise | A small extra energy use, not fat loss |
| Blood vessels | Widen to move heat to your skin | No |
| Appetite and thirst | Many people feel thirsty afterwards | No |
What about "sweating out toxins"?
Sweat is mostly water and salt. Your liver and kidneys deal with waste products, and sweating more doesn't meaningfully speed that up. You may feel lighter and fresher after a sauna, and that's real, but it isn't because you've flushed anything out.
Beware, too, of saunas sold with weight-loss promises, sauna suits and wraps. Wearing plastic to sweat more just dehydrates you faster.
How a sauna habit can still help
None of that means saunas are useless if you're trying to lose weight or get fitter. They can help indirectly, by making the rest of your routine easier to stick to.
- Recovery. Many people find their muscles feel looser and less sore after a sauna, which can make it easier to train again.
- Sleep. A lot of regulars sleep better on sauna days, and good sleep is closely tied to appetite and energy.
- Stress. An hour in the heat with no phone is a genuine break. For some people, that replaces a less healthy way of unwinding.
- Something to look forward to. Pairing a swim, a walk or a training session with a sauna afterwards gives you a reason to show up.
Long-term research from Finland has linked frequent sauna use with better heart health, and researchers suggest saunas may add to the benefits of being active and fit. That's about overall health, not weight, and it's association rather than proof. Our guide to sauna benefits explains what that research did and didn't find.
What about the ice bath?
Cold water makes your body work to stay warm, and there's interesting research on cold exposure and brown fat, a type of fat that burns energy to make heat. A 2021 study of Danish winter swimmers who regularly used sauna and cold water found signs of more active brown fat. It was a small study, and it didn't show weight loss. A cold plunge after a sauna is great for feeling awake. It isn't a shortcut to losing weight.
Don't use a sauna to cut weight
Check with your GP before using a sauna if you have a heart condition, unstable or low blood pressure, are pregnant, or take medication that affects your heart, blood pressure or ability to sweat.
How to use a sauna well if you're getting healthier
Move first
Do your walk, swim or workout, then use the sauna as the cool-down treat.
Keep rounds sensible
Two or three rounds of 8 to 15 minutes is plenty. Our guide on how long to stay in a sauna has more.
Drink water
Bring a bottle and drink before, between rounds and afterwards.
Ignore the scales afterwards
Weigh yourself on a normal day, at the same time, not straight after a sauna.
Make it regular
The benefits people notice, like better sleep and mood, come from going regularly, not from long sessions.
If you want to find a sauna near you to build into your week, browse saunas by county or the sauna map.
