Step on a scale after a long sauna session and the number is often lower. It is tempting to read that as weight loss. It mostly isn’t.
What the scale is showing
Heat makes you sweat, and sweat is water. The drop you see after a sauna is almost entirely fluid, and it returns as soon as you drink — which you need to do. Losing water is not losing fat.
Do you burn calories in a sauna?
Some. Your heart rate rises in the heat, much as it does with light activity, so you use a little more energy than sitting in a cool room. But the effect is small, and saunas have not been shown to reduce body fat on their own. Diet and exercise remain what works.
Where saunas can fit
Many people enjoy a sauna after a workout, and research on regular sauna use has focused on other outcomes — for example, Finnish observational studies linking frequent sauna bathing with lower cardiovascular mortality (Mayo Clinic Proceedings review, 2018). Those are associations in specific populations, not proof that a sauna will change your health or weight.
Don’t use heat to cut weight fast
Sitting in heat to dehydrate yourself before a weigh-in can lead to heat illness and is dangerous without supervision. Drink water before and after sessions, and read our guide to session length and the signs it’s time to get out.
If you are pregnant or have a heart condition or other health concern, ask a doctor before using a sauna.
Frequently asked questions
Why do I weigh less after a sauna?
Mostly because you have lost water as sweat. That weight comes back when you drink and eat, which you should do to rehydrate.
Does a sauna burn fat?
Sitting in a sauna raises your heart rate a little, but the calories used are modest and it is not a substitute for exercise. Research has not shown saunas to be an effective way to lose body fat on their own.
Is it safe to use a sauna to “make weight”?
Deliberately dehydrating to drop weight quickly carries real risks, including heat illness. Do not use a sauna for rapid weight cutting without medical or professional supervision.