You should air out your sauna after every single session, not every other day or whenever you remember. For most home saunas that means leaving the door fully open for 30 to 60 minutes until the interior feels dry to the touch.
After every session. Not every other day. Not when you remember. Every single time you step out, the sauna needs to air out.
Here is why that matters.
Saunas are wet environments by design. Even in a dry Finnish sauna, your body dumps water through sweat. A single 20-minute session can release half a liter of moisture into the air. That moisture settles on the wood, gets absorbed into the benches, and sits in the cracks between the boards. If you seal that moisture in, you are not just risking mold. You are shortening the life of your sauna and potentially creating a breeding ground for bacteria.
The basic rule: air out until the interior feels dry to the touch
For most home saunas, that means leaving the door open for 30 to 60 minutes after each use. If you have a ventilation fan, run it during that window. If your sauna has a window you can crack open, do that too. The goal is to drop the relative humidity inside the sauna back to match the ambient humidity of the room it is in.
I have a friend who built a custom barrel sauna in his backyard. He followed the instructions that came with the kit: "air out after each use." He interpreted that as "leave the door cracked for ten minutes." Six months later, he noticed a musty smell. When he pulled the bench slats, there was black mold growing on the underside. The wood had never fully dried between sessions.
What happens when you skip the air-out
Moisture trapped inside a sauna does three things, none of them good.
- First, it creates conditions for mold and mildew. Wood is porous. When it stays damp for extended periods, mold spores that are always present in the air find a home. Once mold establishes in the wood grain, it is nearly impossible to remove without sanding or replacing the affected boards.
- Second, moisture accelerates wood degradation. Cedar and hemlock, the woods most commonly used in saunas, are naturally rot-resistant, but they are not rot-proof. Constant moisture exposure breaks down the lignin that binds the wood fibers. Over years, the wood becomes soft, spongy, and structurally compromised.
- Third, trapped moisture creates a biofilm on the surfaces you sit on. Sweat contains salts, urea, and bacteria. When that dries between sessions, it is not a big deal. When it stays wet, bacteria multiply. You are essentially sitting on a warm, damp surface that has been inoculated with your own microbes from the previous session.
How long depends on your setup
A traditional Finnish sauna with good ventilation—an intake vent near the heater and an exhaust vent high on the opposite wall—will dry out faster than a poorly ventilated one. If your sauna has mechanical ventilation (a fan pulling air out), you can cut the drying time in half.
Infrared saunas tend to hold moisture differently. Because they operate at lower temperatures (120 to 140°F versus 175 to 195°F for a traditional sauna), the air does not hold as much water vapor. But the surfaces still get damp. The same rule applies: air out after every session.
If you have a sauna in a basement or a room with no windows, you need to be more aggressive. Run a dehumidifier in the room for an hour after each session. Some sauna owners install a small exhaust fan on a timer that runs for 30 minutes after the heater shuts off. That is a smart upgrade if you use your sauna daily.
What about between multiple sessions in one day?
If you are doing back-to-back sessions—say, 20 minutes in the sauna, a cold plunge, then another 20 minutes—you do not need to fully air out between them. Just leave the door open for five minutes between rounds to let the steam clear. The full air-out happens after the last session of the day.
The one time you can skip it
If you live in a dry climate and your sauna has excellent natural ventilation, you might get away with leaving the door cracked for 15 minutes and calling it good. But even then, I would not recommend skipping the air-out entirely. The habit matters more than the exact duration.
A practical protocol
Here is what I do, and what I recommend to anyone who asks:
- After your last session of the day, open the door fully. If your sauna has a top vent, open that too. Leave it for at least 30 minutes.
- If you have a towel or a sponge, wipe down the benches and backrests while the sauna is still warm. This removes the sweat residue that feeds bacteria and reduces the moisture load the wood has to absorb.
- Once the interior feels dry to the touch, close the door but leave it slightly ajar—just enough to allow continuous airflow. Some sauna doors have a magnetic latch that lets you set a gap. If yours does not, stick a folded towel between the door and the frame.
- Check the floor. Water often pools under the benches. If your sauna has a drain, rinse it out. If it does not, mop up any standing water with a towel.
Air out your sauna after every use. Leave the door open for 30 to 60 minutes. Wipe down the surfaces. Keep the ventilation running. Do this consistently, and your sauna will last decades without developing the musty smell that signals trapped moisture.
Skip it, and you will eventually have a problem. The question is not whether, but when.
Frequently asked questions
How long should you leave a sauna door open after use?
Leave the door fully open for at least 30 to 60 minutes after your last session of the day. If your sauna has a ventilation fan, run it during that window. Once the interior feels dry to the touch, you can close the door but keep it slightly ajar to allow continuous airflow.
What happens if you don't air out your sauna?
Trapped moisture creates conditions for mold and mildew to grow in the wood grain, which is nearly impossible to remove without sanding or replacing the affected boards. It also accelerates wood degradation over time and allows bacteria from sweat to multiply on the surfaces you sit on.
Do you need to air out an infrared sauna after every session?
Yes, the same rule applies to infrared saunas even though they operate at lower temperatures than traditional saunas. The surfaces still get damp, so you should air out after every session just as you would with any other sauna type.
Do you need to air out a sauna between back-to-back sessions?
If you're doing multiple rounds in one day, you don't need a full air-out between them. Just leave the door open for five minutes between rounds to let steam clear, then do the full 30 to 60 minute air-out after your last session of the day.