A sauna used regularly collects sweat, body oils, bacteria, and mineral deposits on every surface. Cleaning a sauna requires special attention because most of the interior is wood — and wood in a high-heat, high-humidity environment is sensitive to both moisture saturation and harsh chemicals. This guide covers routine sauna maintenance, deep cleaning wood benches and walls, cleaning the heater and sauna rocks, and ongoing care to prevent mold and odors.
What You’ll Need
Tools
- Soft-bristle brush (natural bristle or nylon)
- Microfiber cloths
- Bucket
- Sauna-specific scrubbing brush (long-handled for benches)
Materials
- Warm water
- Mild dish soap or sauna-specific cleaner (Helo, Harvia sauna cleaner)
- White vinegar (for mold treatment)
- Baking soda (for stubborn staining and odors)
- Sauna wood treatment oil (teak oil or sauna bench oil) — for conditioning wood after cleaning
What NOT to Use
- Bleach — corrodes the sauna heater and metal components, damages wood grain, leaves toxic residue that releases fumes when heated
- Strong chemical cleaners (oven cleaner, abrasive powders) — damage wood and leave residues that off-gas at sauna temperatures
- Excessive water — sauna wood is designed to handle moderate moisture from steam, not soaking or water pooling
Safety Precautions
- Clean when the sauna is completely cool — wood is expanded when hot and cleaning hot surfaces drives cleaning solutions deeper into the grain.
- Ventilate after cleaning — leave the sauna door open and run the heater briefly (empty, no one inside) after cleaning to dry the wood and heat off any remaining cleaning product before the next use.
- Never clean sauna rocks with chemicals — sauna rocks are porous and absorb chemical cleaners. Chemical residue released as steam during sauna use is inhaled directly.
How to Clean a Sauna Step by Step
Step 1: Daily Quick Clean (After Each Use)
After every sauna session, wipe down the benches with a damp cloth to remove sweat before it dries and soaks into the wood. Open the door and ventilate for at least 30 minutes after use. Ask all users to sit on a clean towel during sauna use — this single practice reduces bench cleaning dramatically by preventing direct skin contact with the wood.
Step 2: Weekly Bench and Wall Scrub
Mix a small amount of mild dish soap in a bucket of warm water. Using a soft-bristle brush, scrub the bench surfaces, backrests, and walls with the grain of the wood. Work in sections. The scrubbing motion lifts embedded oils and bacteria from the wood grain. Wipe immediately with a clean damp cloth to remove the soap, then wipe again with a plain water cloth to rinse. Don’t let soapy water pool on the floor or soak into bench joints.
Step 3: Deep Clean with Sauna Cleaner or Vinegar
For a monthly deep clean, use a purpose-made sauna cleaner (available from Harvia, Helo, or Finlandia sauna supply brands) — these are formulated to clean effectively without damaging sauna wood or leaving harmful residue. Alternatively, a solution of 1 part white vinegar to 5 parts warm water works well: vinegar kills bacteria and mold without bleach risks, and the acidic odor dissipates completely when the sauna heats up. Apply with a cloth or brush, scrub, then rinse and dry thoroughly.
Step 4: Treat Mold and Mildew
Sauna benches that aren’t dried and ventilated after use develop mold in the pores of the wood — often appearing as black or grey spots on the underside of benches or along wall-bench junctions. Mix undiluted white vinegar in a spray bottle and apply directly to the affected area. Let sit for 15 minutes, then scrub with a brush and wipe clean. For persistent mold that doesn’t respond to vinegar, a hydrogen peroxide (3%) spray left for 10 minutes is more effective without bleach’s risks. Sand mold-affected wood lightly with 120-grit sandpaper if it has penetrated the surface — always follow sanding with wood oil conditioning.
Step 5: Clean the Sauna Floor
Sauna floors receive the most contamination — water poured for steam, sweat dripping, and tracked-in dirt. Scrub the floor with the same mild soap solution, then rinse thoroughly. For wooden floors, avoid soaking — a quick scrub and rinse followed by thorough drying is the correct approach. For sauna rooms with tiled floors, a standard floor cleaner is fine. Ensure floor drains are clear and functional — a backed-up floor drain is the primary cause of persistent sauna moisture problems.
Step 6: Clean the Sauna Heater
The sauna heater (kiuas) itself requires minimal cleaning. Wipe the exterior of the heater unit with a dry or barely damp cloth when the heater is completely cool. Use no water on the heater elements. Check that the heater’s air intake vents are clear of debris. For electric heaters, a soft brush to remove dust from the exterior is the extent of appropriate cleaning.
Step 7: Clean or Replace Sauna Rocks
Sauna rocks absorb minerals from water poured on them and can crack over time from thermal cycling. Never clean sauna rocks with soap or chemical cleaners — they absorb everything poured on them and release it as steam. Clean sauna rocks by: removing them when cool, rinsing under cold running water while scrubbing with a stiff brush (no soap), allowing to dry completely, and checking for cracked or fragmented rocks (cracked rocks can shatter dangerously when heated — replace any with visible fractures). Replace the full rock bed every 3–5 years or when rocks become fragmented.
Step 8: Condition the Wood
After cleaning, especially after a deep clean or after sanding to remove mold, treat all wood surfaces with a sauna-specific bench oil or food-grade oil (linseed oil works). Apply with a cloth, allow to penetrate for 15–20 minutes, then wipe off excess. This conditions the wood, restores its natural oils depleted by heat and sweat, and creates mild water resistance. Never use standard furniture oils or varnish inside a sauna — they peel at high temperatures and release fumes.
Sauna Cleaning Schedule
| Task | Frequency |
|---|---|
| Post-use bench wipe and ventilation | After every use |
| Full bench and wall scrub | Weekly |
| Deep clean (sauna cleaner or vinegar) | Monthly |
| Floor scrub | Weekly or after heavy use |
| Sauna rock inspection and rinse | Every 3–6 months |
| Wood oil conditioning | Every 6–12 months or after deep cleaning |
| Full rock replacement | Every 3–5 years |
Frequently Asked Questions
Why does my sauna smell bad even after cleaning?
Persistent sauna odor after cleaning usually means mold is established in the wood grain below the surface, or in an area that isn’t being reached (under benches, behind heater, floor drain). Inspect every surface systematically — particularly the underside of benches and the junction where benches meet the wall. If the wood is dark-stained with mold that doesn’t respond to surface cleaning, those boards may need replacing rather than further cleaning.
Can I power wash the inside of a sauna?
No — pressure washing forces water deep into wood joints and through the wall vapor barrier, causing long-term moisture damage, warping, and mold behind the walls. Hand scrubbing with a brush and minimal water is the correct approach. Some commercial sauna cleaning services use low-pressure steam cleaning (not water pressure washing) which is acceptable because the moisture evaporates quickly in a heated environment.
How do I prevent my sauna benches from turning grey?
The grey patina that develops on sauna wood over time is a combination of salt from sweat oxidizing the wood surface and UV exposure if the sauna has windows. Using towels on benches prevents sweat contact with the wood, slowing the graying process. Annual light sanding (120-grit) followed by wood oil conditioning restores color and grain. The graying is not harmful but can be aesthetically remedied with periodic conditioning.
Is it safe to use essential oils on sauna rocks?
Pure sauna essential oil blends (diluted in water before pouring on rocks) are designed for sauna use and are safe in small quantities. Never pour undiluted essential oils on sauna rocks — concentrated oils burn and produce irritating smoke rather than pleasant steam. Commercial sauna essence blends (Helo, Karhu sauna essence) are pre-diluted to appropriate concentrations. Standard aromatherapy essential oils not specifically designed for sauna use may not be safe at sauna temperatures.
Conclusion
Keeping a sauna clean is mostly about habits — drying and ventilating after every use, quick bench wipes, weekly scrubbing, and annual wood conditioning. The work is minimal compared to the damage that builds up in a neglected sauna. A clean sauna smells of fresh wood and steam, not old sweat, and its surfaces stay smooth and splinter-free for a decade or more with proper care.
For related home spa maintenance, see our guide on how to clean a spa filter if you have a hot tub alongside your sauna. For cleaning a slate hearth near a steam room, our guide on how to clean a slate hearth covers stone surfaces in high-humidity environments.
