Do saunas detox you or help you lose weight?

Why do you weigh less after a sauna?

Because you’ve sweated. In a typical session, a person sweats around half a kilo, and more in a long or very hot session. A Polish study of 674 students who spent two 10-minute spells in a dry sauna found that weight lost went up with body size: heavier people lost more, and the authors warned they were at higher risk of dehydration.

None of that is fat. As soon as you drink, the weight comes back. Using the scales after a sauna as a measure of progress is misleading.

Does sweating remove toxins?

Sweat is mostly water, with salt and small amounts of other substances. A systematic review of 24 studies found that sweat can contain arsenic, cadmium, lead and mercury, and that in people with high exposure the amounts can be meaningful. But:

• The studies were small and measured sweat in different ways.
• None showed that regular sweating lowers the body’s levels or improves health in ordinary people.
• Your kidneys and liver do the real work of clearing waste and toxins, and they don’t need a sauna’s help.

“Detox” saunas and blankets that promise to flush out toxins, cellulite or “impurities” are making claims that the evidence doesn’t support.

Is there any metabolic benefit?

Heat raises your heart rate, so you burn slightly more energy than sitting still, but far less than walking. In one trial, adding saunas after exercise improved fitness, blood pressure and cholesterol a little more than exercise alone (see blood pressure). Fat loss came from the exercise.

How do you stay safe?

Drink water before and after, don’t use a sauna to make weight, and leave if you feel dizzy, sick or have a headache: those can be early signs of dehydration or heat exhaustion. See hydration.