We don't recommend wearing your watch in the sauna.
Saunas create strong temperature fluctuations, heat and humidity. These conditions can put strain on seals, lubricants, leather straps and other materials.
Even a water-resistant watch isn't automatically suitable for the sauna or steam room. Water resistance is tested under different conditions and doesn't reliably protect against heat and extreme temperature changes.
So take your watch off before going into the sauna and keep it in a dry, protected place.