by Quick answer: Identify the smell first. New-mattress chemical odor is off-gassing from foam, harmless, temporary, fixed with ventilation. A musty or sour smell on an older mattress signals trapped moisture and possible mold. For most odors: sprinkle baking soda generously, leave it overnight, vacuum thoroughly, then air the mattress out near an open window or in sunlight.
By the MattressNut editorial team · Updated June 2026
New Mattress Smell: Off-Gassing Explained
Unbox a foam mattress and you may notice a sharp chemical smell within the first few hours. That's off-gassing, volatile organic compounds (VOCs) released as the foam expands and the materials stabilize after being compressed and sealed in plastic. It's normal, and for most people it's harmless.
How long does it last? Usually a few hours to a couple of days. In rooms with poor airflow, some foam mattresses can take up to two weeks to fully clear. The fix is straightforward:
- Unwrap the mattress in a well-ventilated room, ideally not the bedroom you plan to sleep in immediately.
- Open windows on both sides of the room to create cross-ventilation.
- Run a box fan pointed toward an open window to push air out.
- Give it at least 24-48 hours before sleeping on it if the smell is strong.
If you're concerned about emissions, look for CertiPUR-US certification. Foams carrying that label have been tested for harmful VOC levels and meet lower-emission standards, it's the clearest signal available when you're shopping.
How to Get Rid of Mattress Smell With Baking Soda
For general odors, sweat smell, or a mattress that's lost its fresh scent over time, baking soda is the most reliable DIY method. It absorbs odor and moisture rather than masking them with fragrance.
Step-by-step
- Strip the bed completely. Remove all sheets, protectors, and toppers.
- Spot-clean any stains first. Odor often comes from a stain source. Blot (don't rub) with a damp cloth; for sweat or urine, an enzyme cleaner breaks down the proteins causing the smell. Let it dry fully before moving on.
- Sprinkle a generous, even layer of baking soda across the entire surface. Don't be stingy, a light dusting won't reach deep enough.
- Leave it for several hours. For mild odor, four hours is enough. For stronger smells, leave it overnight or up to 24 hours.
- Vacuum it up with an upholstery attachment. Go slowly, in overlapping passes, so you pull up as much residue as possible.
- Air the mattress out. Open the windows after vacuuming. If you can prop the mattress against a wall near sunlight, even briefly, UV exposure helps further.
- Flip and repeat on the other side if the odor persists or if you haven't treated the underside in a while.
One pass usually handles everyday odor. For heavier buildup, two rounds a week apart gets there.
Musty Smell: Moisture, Mold, and Humidity
A musty or mildew-like smell is different from off-gassing or general body odor, it points to moisture trapped in the mattress. That moisture can come from sweat over time, a spill that didn't dry fully, or a humid room where condensation collects under the mattress.
Left unaddressed, persistent moisture creates conditions for mold and mildew to grow inside the foam or springs. Some signs it's gone that far: the smell returns quickly after baking soda treatment, or you see dark spotting on the fabric or around seams.
If the mold is surface-level and caught early, some people treat it with a diluted rubbing alcohol solution (check the manufacturer's care instructions first). But mold that has penetrated the foam layers isn't salvageable, a replacement is the safer call, for both hygiene and respiratory health.
Preventing Odor From Coming Back
Most mattress smell is preventable with a few habits:
- Use a mattress protector. A waterproof protector stops sweat, spills, and body oils from reaching the foam. Wash it every one to two months.
- Air your bedding weekly. Pull back the sheets and duvet each morning for 20-30 minutes before making the bed. This lets moisture from overnight sleep evaporate instead of sitting against the mattress.
- Control room humidity. Keep bedroom humidity below 50%. A dehumidifier helps in humid climates or during summer months. Low humidity cuts mold risk significantly.
- Rotate the mattress every three to six months. Rotating changes the wear pattern and moves any moisture-prone zones around, helping the whole mattress breathe more evenly over time.
Frequently Asked Questions
Is new mattress off-gassing harmful?
For most people, no. The VOCs released by foam mattresses during off-gassing are at low levels and dissipate quickly with ventilation. People with asthma, chemical sensitivities, or young children may want to be more cautious, ventilate the room for 48-72 hours and sleep elsewhere until the smell is gone. CertiPUR-US certified foams have been independently tested for harmful emissions and meet established thresholds.
How long does new mattress smell last?
Most off-gassing smell clears within 24 to 72 hours with good ventilation. In a poorly ventilated room with dense foam, it can linger up to two weeks. Running a fan and opening windows speeds the process considerably.
Does baking soda actually remove mattress odor or just cover it?
It absorbs it. Baking soda (sodium bicarbonate) neutralizes acidic odor molecules and pulls moisture out of the surface fibers, it doesn't add a scent to mask the problem. That said, it works best on surface-level odor; deeply embedded smells from mold or years of moisture buildup may not fully clear.
What causes a musty smell on an older mattress?
Trapped moisture, most commonly from sweat accumulating over time. Without a mattress protector, body sweat passes through the sheets and slowly saturates the top layers of foam or padding. Combined with body heat, that creates ideal conditions for mold and mildew. High room humidity accelerates it.
Can I get rid of mold smell in a mattress?
Surface mold caught early can sometimes be treated, but foam that has mold growing inside it is not recoverable. If the musty smell returns within days of a baking soda treatment, or if you see dark spotting on the fabric, replacing the mattress is the practical answer. Sleeping on a moldy mattress carries real respiratory risk.
How do I stop my mattress from smelling in the future?
Three things make the biggest difference: a waterproof mattress protector (washed monthly), airing the bed out each morning before making it, and keeping bedroom humidity below 50%. These habits together prevent the moisture buildup that causes almost all non-new-mattress odor.
When It's Time to Replace
Surface odors, off-gassing, sweat smell, general mustiness, are fixable. A mattress with mold in the foam layers, or one that's sagging and holding moisture regardless of what you do, is a health and sleep quality problem that baking soda won't solve.
If you're shopping for a replacement, the Saatva Classic is worth a look, it includes free white-glove delivery and removal of your old mattress, so the smelly one is gone on delivery day. See the Saatva Classic and its 365-night trial.
Bottom line: New smell = off-gassing, ventilate and wait. Old or musty smell = baking soda, sun, and humidity control. Persistent mold smell = replace.