Can I go in a sauna while fasting?

Sweating doesn't break the fast

The fast is broken by what you take in (food, drink, intimacy), not by what leaves your body like sweat. Heat on your skin is fine too. The Prophet ﷺ was seen pouring water over his head while fasting because of thirst or heat (Sunan Abi Dawud 2365). So cooling down or warming up your body doesn't affect your fast. See Does showering break my fast?

What about steam rooms?

A dry sauna is simple. In a steam room or a sauna where water is thrown on the stones, you breathe moist air. Most scholars say normal breathing in a steamy room doesn't break the fast, just like a hot shower. Some advise avoiding deliberately inhaling thick steam, since water could reach the throat. If you go, breathe normally and don't sit with your face over the steam.

Why your health matters more here

A 15-minute sauna can make you lose a lot of fluid. After a full day without water, that can bring on dizziness, headaches, low blood pressure or fainting. Islam doesn't want you to harm yourself:

• Best time: after iftar, once you've had water and something to eat.
• If you go before sunset: keep it brief, sit on a lower bench where it's cooler, and leave at the first sign of dizziness.
• Skip it if you have heart problems, low blood pressure or are pregnant, and follow your doctor's advice.
• If you faint or feel seriously unwell, drink. You can break the fast when your health is at risk and make up the day later.

The same thinking applies to hard workouts. See Can I exercise while fasting in Ramadan?

Don't forget the modesty side

Many European saunas are mixed and some are nude-only. That's a separate question from fasting, and it matters all year. For the details, see Can I still go to the sauna as a Muslim?