Most people overthink how to clean a sauna. They assume it needs special products, sealants, or a deep scrub every week. It doesn't. A sauna is a hot, cedar-lined room that dries itself out if you let it, and the biggest thing you can do to keep it clean is simply to let it dry properly after every use. The actual cleaning is quick, cheap, and mostly water.

The reason this matters is that a sauna gets genuinely wet during a session. Between löyly (water on the rocks), sweat dripping through the bench slats, and moisture from breathing, the wood absorbs a lot of water every time you use it. If that moisture sits, you get stains, odors, and eventually mold. If it dries out, the wood stays light, clean, and lasts for decades. So most of "cleaning" is really about drying.

Here's the routine I use and recommend to clients, broken down by how often you actually need to do each part.

The Daily Cleaning: Rinse and Dry

The simplest habit is to keep a stiff-bristle hand brush and a bucket of plain water in the sauna. When the last person is done, they dip the brush and give the benches, backrests, and floor a quick scrub — just water, no soap. This knocks off the sweat and body oils before they have a chance to soak in and stain. It takes about a minute.

Then you dry the sauna out, which is the part people skip. After your session, prop the duckboards (the removable floor slats) up off the floor so air can get underneath, leave the door open, and let the residual heat in the rocks and wood finish drying everything. If you built the sauna with a proper drying vent — a vent high on the wall you open after use — crack that too. The leftover heat plus airflow will pull the moisture out on its own.

This is where good ventilation earns its keep. A sauna that can't dry between sessions is fighting a losing battle against mold no matter how often you scrub it. If your sauna feels damp or smells musty hours after you've used it, the problem isn't your cleaning — it's the drying, and you should look at your sauna ventilation before anything else.

The Weekly Cleaning: A Gentle Wash

Once a week, or after heavy use, do a slightly more thorough pass. Fill your bucket with warm water and add a small amount of mild dish soap or a cleaner made specifically for sauna wood. Scrub the benches, backrests, and any spots where people sit or lean, then wipe down with clean water so you're not leaving soap residue behind.

Keep the soap gentle and the amount small. You're cutting body oils and light staining, not degreasing an engine. Harsh cleaners, bleach on a routine basis, or anything with a strong fragrance can soak into the wood and off-gas when the sauna heats up — which is unpleasant and defeats the purpose of a clean sauna. Save the stronger stuff for actual problems.

Pay attention to the floor under the benches. Sweat drips through the bench slats continuously during a session and collects on the floor below. If your benches have open fronts — which is how we build them, and how they should be built — you can reach under and scrub the floor easily. If your bench fronts are fully enclosed, cleaning that hidden space is difficult and moisture accumulates where you can't get to it. That's one of the reasons we avoid enclosed bench fronts entirely; a sauna you can't clean under is a hygiene problem waiting to happen.

Dealing With Stains and Spots

Even with a good routine, you'll get the occasional stain — a dark sweat mark on the bench, a discolored patch where someone always sits. These come out without much trouble.

For general staining, make a paste of baking soda and water, spread it on the spot, let it sit for a few minutes, then scrub with your brush and rinse. Baking soda is mild, cheap, and won't hurt the wood. For tougher discoloration, warm water with a bit more detergent and some elbow grease usually does it.

If you find actual mold — fuzzy growth, black spots that don't scrub off with soap — that's a different situation. You can spot-treat it with a diluted bleach solution (roughly one part bleach to ten parts water), scrub, and rinse thoroughly. But if mold keeps coming back, cleaning is only treating the symptom. Recurring mold means the sauna isn't drying out properly, and you need to fix the underlying moisture problem. We wrote a full guide on how to prevent mold in a sauna that walks through the ventilation and drying setup that keeps it from returning.

The Annual Cleaning: Sand and Refresh

Once a year, the benches benefit from a light sanding. Over a season of use, the wood where people sit gets darker and can feel slightly rough. A quick pass with 120 to 220 grit sandpaper — by hand or with an orbital sander — takes off the top layer, brings back the original light color, and smooths the surface. It's one of the more satisfying pieces of sauna maintenance because the benches genuinely look new afterward.

Sand along the grain, wipe off the dust, and that's it. You do not need to apply anything after. Which brings us to the most important rule of sauna cleaning.

Never Seal or Varnish the Interior Wood

This is the one thing people get wrong that actually causes damage. It's tempting to treat sauna wood the way you'd treat a deck or furniture — sand it, then seal it with a finish to protect it. Don't. Do not varnish, polyurethane, stain, or seal the interior wood of a sauna.

There are a few reasons. A sealed surface gets much hotter to the touch than bare wood, so your benches become uncomfortable or unusable. Any finish will off-gas fumes when it hits 180 to 200°F, which you're then breathing. And sealing the wood takes away the soft quality of heat and steam penetrating into the surface that makes a good sauna feel the way it does. Bare, untreated cedar or hemlock is what you want — it's naturally moisture and decay resistant, and it's meant to be left alone.

The one exception some people make is a dedicated food-safe paraffin sauna oil on the benches, applied sparingly, specifically formulated for sauna use. Even that is optional and mostly cosmetic. If you're keeping the sauna dry and clean, the wood doesn't need it. Cedar has done fine in Finnish saunas for a very long time with nothing on it but water. If you're still choosing materials, our guide to the best wood for a sauna covers why species choice affects how the interior holds up over time.

Don't Forget the Rocks and the Heater

The stones on your heater aren't permanent. Over time, thermal cycling breaks them down — they crack, crumble, and pack together, which chokes off airflow and hurts steam quality. Once a year, pull the rocks out, throw away any that are cracked or crumbling, rinse the good ones to clear out debris and mineral scale, and restack them loosely so water and air can move through. If you're using the right stones (olivine diabase or peridotite) they'll last a while, but they still need this periodic reset.

Wipe down the heater casing when it's cool, clear any debris that's fallen into the rock cavity, and check that nothing is blocking the elements. This isn't so much cleaning as it is keeping the heater doing its job.

What a Clean Sauna Routine Actually Looks Like

Put together, none of this is a burden. After each session, a quick water scrub and then prop the floor up and let it dry. Once a week, a gentle soapy wash and rinse. Once a year, sand the benches and service the rocks. Spot-treat stains and mold as they come up, and never put a finish on the interior wood. That's the whole thing.

The saunas that go bad are almost never the ones that missed a scrubbing. They're the ones that never got a chance to dry out, so if you only take one thing from this: build and use your sauna so it dries completely between sessions, and the cleaning stays easy for the life of the sauna. A well-designed sauna makes this automatic — good ventilation, open bench fronts, and a floor you can reach do most of the work for you.

Frequently Asked Questions

How often should you clean a sauna?

Do a quick water rinse of the benches after every session and let the sauna dry out fully. A gentle soapy wash once a week (or after heavy use) handles the deeper cleaning, and a light bench sanding once a year keeps the wood looking new. The daily drying matters more than any single scrub.

What should you use to clean sauna wood?

Plain water for the daily rinse, and mild dish soap or a dedicated sauna cleaner for the weekly wash. Baking soda paste removes most stains, and a diluted bleach solution handles actual mold. Avoid harsh or heavily fragranced cleaners — they soak into the wood and off-gas when the sauna heats up.

Can you use bleach in a sauna?

Only for spot-treating mold, and diluted (about one part bleach to ten parts water), followed by a thorough rinse. Don't use bleach as a routine cleaner. If mold keeps returning, the real fix is better drying and ventilation, not more bleach.

Should you seal or varnish sauna wood?

No. Never varnish, stain, or seal the interior wood of a traditional sauna. A finish makes the wood hotter to the touch, off-gasses fumes at sauna temperatures, and ruins the soft feel of the heat. Leave cedar and hemlock bare — they're naturally moisture resistant and meant to be untreated.

Why does my sauna smell musty?

A musty smell almost always means the sauna isn't drying out between sessions, so moisture is sitting in the wood. Prop up the duckboards, leave the door open, and use a drying vent after each session. If the smell persists, your ventilation setup likely needs work — poor drying is the root cause of both odor and mold.

Next Steps

Cleaning is the easy part once the sauna is designed to dry itself. If yours holds moisture, smells musty, or grows mold no matter how often you scrub, the problem is in the build — usually ventilation or bench design — not your routine. That's exactly the kind of thing we catch before it becomes a problem. If you're planning a sauna or fighting an existing one, our remote sauna design service can review your layout and ventilation from anywhere in the country, or start with the free sauna design checklist to make sure the fundamentals are right.