How to Remove Odour from a Mattress

Reading time: approximately 8 minutes

Not all mattress smells are the same, and not all treatments work on all smells. This matters more than most people realise. Baking soda, for example, is widely recommended as a universal mattress odour remedy -- but it is only genuinely effective for body odour and as a finishing step after other treatments. It does nothing meaningful for off-gassing VOCs, will not kill mould, and only masks urine odour temporarily without addressing the cause.

This guide covers all five types of mattress odour, what causes each one, and the specific treatment that actually works. If you are dealing specifically with urine odour (from pets or people), our dedicated articles go deeper: see our guides on removing persistent urine smell and removing pee smell from pet and child accidents.

Type 1: New Mattress Off-Gassing

A new mattress smell -- sometimes described as chemical, sweet-chemical, or "new car" smell -- comes from volatile organic compounds (VOCs) released as the foam or adhesives in the mattress cure and off-gas. Memory foam and polyurethane foam mattresses are the most common sources. The compounds involved include isocyanates, polyols, and various blowing agents used in the foam manufacturing process.

Off-gassing is at its strongest in the first 24 to 72 hours. In a well-ventilated room, the smell typically becomes unnoticeable within 3 to 7 days. In a small, poorly ventilated bedroom, it can linger for 2 to 3 weeks.

What actually works for off-gassing:

• Air the mattress in a ventilated room with windows open and a fan running for at least 24 hours before covering with bedding
• If possible, place the mattress outdoors in the shade for a few hours (direct UV can degrade foam over time, so avoid prolonged direct sun)
• Do not use baking soda -- it will not absorb VOCs and may leave residue in the foam
• Do not use fabric sprays or air fresheners to mask the smell -- these add more VOCs to an already VOC-heavy situation
• Open bedroom windows while sleeping for the first week if the smell is noticeable in the room

Type 2: Sweat and Body Odour

This is the gradual, slightly sour or slightly sweet smell that builds up in a mattress over months and years of use. It comes from sweat, skin oils, and skin cell debris that passes through bedding and accumulates in the top layers of the mattress. It is accelerated by sleeping hot, using heavy blankets, or not using a mattress protector.

Body odour compounds in sweat include lactic acid, fatty acids, and various bacterial metabolites (the characteristic smell of sweat is produced by skin bacteria consuming the raw compounds in perspiration). These are protein-based and respond well to enzymatic cleaners, though a simpler baking soda treatment is usually sufficient for routine buildup.

Treatment for sweat/body odour:

1. Strip the mattress completely and allow it to breathe in an aired room for several hours
2. Sprinkle baking soda generously over the entire sleeping surface (not just odorous spots)
3. Leave for 6 to 12 hours, then vacuum off with an upholstery attachment
4. For persistent or strong body odour, follow the baking soda step with a light mist of diluted white vinegar (1:1 with water), allow to dry, then a second round of baking soda
5. Fit with a breathable, washable mattress protector going forward -- this is the permanent solution to sweat odour buildup

Type 3: Urine Odour

Urine odour is distinct from body odour -- it has a sharper ammonia quality, and it tends to be localised to a specific area of the mattress rather than distributed across the sleeping surface. It is caused by uric acid crystals that form as urine dries and reactivate with warmth and humidity.

The key treatment requirement is an enzymatic cleaner with urease or protease enzymes, applied with sufficient contact time (20 to 45 minutes, covered with plastic wrap to prevent evaporation). Baking soda alone and vinegar alone do not break down uric acid -- they only temporarily mask the ammonia smell.

For the full urine odour treatment protocol, including why the smell returns after cleaning and the multi-step approach for deeply penetrated stains, see our dedicated guide on how to remove urine smell from a mattress.

Type 4: Mildew and Mould Smell

Mould smell is distinct from all others -- it has an earthy, musty, sometimes slightly sweet quality that is hard to confuse with body odour or urine once you know what it is. It is caused by mould or mildew growing in the mattress, which happens when moisture is trapped in the foam without adequate drying.

Common causes of mould in mattresses:

• Placing a mattress directly on the floor or on a solid platform with no airflow underneath
• Sleeping on a mattress in a high-humidity room without adequate ventilation
• A liquid spill or urine accident that was not fully dried before replacing bedding
• A mattress in a basement or on a concrete slab where moisture migrates upward

To check for mould, remove all bedding and look for dark spotting (grey, black, or greenish) on the mattress surface or under the mattress. Also check the base or platform -- mould in a mattress is sometimes actually mould on the surface the mattress rests on, which then transfers upward.

Surface treatment (cover mildew only):

1. Move the mattress to a well-ventilated space or outdoors
2. Spray affected areas with undiluted white vinegar and allow to sit for 1 hour
3. Blot, then spray with 3% hydrogen peroxide and allow to sit for 20 minutes
4. Blot dry thoroughly, then place in direct sunlight (UV light kills surface mould spores)
5. Allow to dry completely -- at least 6 to 8 hours -- before returning indoors

Type 5: The Musty Old Mattress Smell

A mattress that has been used for 7 or more years often develops a low-level musty smell that is not quite mould, not quite body odour, and not quite anything else easily named. This is the accumulated smell of dust mite waste products and the breakdown of skin cells that have settled into the mattress over years of use.

Dust mites are microscopic arachnids that live in mattresses and bedding, feeding on shed skin cells. A typical mattress that has not been regularly covered and washed can house millions of them. Their waste products -- particularly guanine, a compound in their droppings -- produce the characteristic dusty, stale smell of an old mattress. These compounds also trigger allergic reactions in sensitive individuals.

For the old mattress smell, the most effective home treatment is a combination of a generous baking soda treatment (leave for 12 or more hours, vacuum thoroughly) and placing the mattress in direct sunlight if possible. UV light destroys dust mite proteins on the surface. A dust-mite-proof encasement going forward will prevent future accumulation.

Related Reading

• How to Remove Urine Smell from a Mattress (Persistent Odour)
• How to Remove Pee Smell from a Mattress (Pet and Child)
• How to Remove Pee Stains from a Mattress
• Urine Remover for Mattress: Buyer's Guide
• How to Remove All Types of Mattress Stains

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Mattress Miracle -- 441½ West Street, Brantford, ON -- (519) 770-0001

Hours: Monday--Wednesday 10am--6pm, Thursday--Friday 10am--7pm, Saturday 10am--5pm, Sunday 12pm--4pm.

If your mattress smells and you are not sure whether to clean it or replace it, bring your questions to Brad, Dorothy, or Talia at our West Street showroom. We have been giving honest, practical sleep advice to Brantford families since 1997 -- including the straightforward ones like "yes, this mattress should go."

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