Why Does My Mattress Smell? Off-Gassing, Mould & Odour Removal Guide (2026)

A smelly mattress is more than an annoyance. Depending on the source, it can signal chemical exposure from a new mattress, hygiene issues from an aging one, or even mould growth that poses genuine health risks. The cause determines the solution, so the first step is identifying what you are actually smelling.

New Mattress Smell: Off-Gassing Explained

If your mattress is brand new, the smell is almost certainly off-gassing. This is a normal chemical process that occurs when foam materials (memory foam, polyurethane foam, gel foam) release trapped volatile organic compounds (VOCs) into the air.

Why New Mattresses Smell

Foam is manufactured using chemical processes that leave residual compounds in the finished product. When the mattress is sealed in plastic packaging (especially bed-in-a-box mattresses that are compressed and vacuum-sealed), these compounds have nowhere to go. The moment you open the packaging and the foam expands, the VOCs are released into the air.

The smell is most noticeable in the first few hours after unboxing. For most quality mattresses, the smell dissipates within 24 to 72 hours. Budget mattresses with lower-quality foam may off-gas for up to a week. In rare cases with particularly cheap foam, the smell can linger for two to three weeks.

Which Mattress Types Off-Gas Most?

Bed-in-a-box mattresses tend to off-gas more than mattresses purchased in-store because they have been compressed and sealed in plastic for days or weeks, concentrating the VOCs. Showroom mattresses have already off-gassed during their time on display, which is one advantage of buying from a physical store.

What Are VOCs and Are They Harmful?

VOCs (volatile organic compounds) are gases released by certain solid or liquid materials. In mattresses, the most common VOCs include:

• Formaldehyde: Used in adhesives that bond foam layers. A known irritant at high concentrations.
• Benzene: A byproduct of some foam manufacturing processes.
• Toluene: Found in some polyurethane foam formulations.
• Methylene chloride: Sometimes used in foam blowing agents.

Are these dangerous? At the concentrations found in certified mattresses, the health risk is very low. A 2019 study published in Environmental Science & Technology (Boor et al.) measured VOC emissions from new mattresses and found that concentrations dropped to near-ambient levels within 24-48 hours of unboxing in a ventilated room. The initial burst of VOCs, while unpleasant-smelling, was well below regulatory safety thresholds.

8 min read

How to Speed Up Off-Gassing

If your new mattress smells, these steps will help clear the odour faster:

1. Unbox in a well-ventilated room. Open windows and run a fan if possible. Cross-ventilation (windows on opposite sides of the room) is most effective.
2. Remove all plastic packaging immediately. Do not leave the mattress partially wrapped; this traps VOCs against the foam surface.
3. Wait before making the bed. Leave the mattress bare (no sheets, protector, or topper) for the first 24 to 48 hours. Bedding traps odours against the surface.
4. Sprinkle baking soda. Apply a thin layer of baking soda across the entire surface. Baking soda absorbs odour molecules. Leave for 4 to 8 hours, then vacuum thoroughly.
5. Use an air purifier. A purifier with an activated carbon filter is specifically designed to capture VOCs. Place it in the same room as the new mattress.
6. Give it time. Most off-gassing resolves on its own. If the smell persists beyond 7 to 10 days, contact the retailer.

What not to do: Do not use air fresheners, scented sprays, or fabric softener to mask the smell. These products add their own chemical compounds on top of the VOCs, which can make the situation worse for people with chemical sensitivities.

Old Mattress Smell: Six Common Causes

If your mattress is not new but has developed a smell over time, the cause is one of these:

1. Sweat and Body Oils

The average person produces about 200 mL of sweat per night. Over months and years, this moisture (along with body oils and dead skin cells) soaks through sheets and protectors into the mattress. The result is a musty, stale odour that builds gradually.

2. Dust Mites

Dust mites feed on dead skin cells and thrive in the warm, humid environment inside a mattress. Their waste products and decomposing bodies contribute to a stale, slightly sweet smell. A study in the Journal of Allergy and Clinical Immunology found that the average mattress contains between 100,000 and 10 million dust mites after two years of use.

3. Mould and Mildew

Mould produces a distinctive musty, earthy smell. If your mattress smells damp or earthy, mould is the likely culprit. Mould grows when moisture gets trapped inside the mattress with insufficient airflow. This is particularly common in Canadian homes during humid summers and in basements where air circulation is poor.

4. Pet Odour

Pet dander, fur, urine, and drool can penetrate a mattress quickly, especially without a waterproof protector. Pet odours are particularly persistent because the proteins in pet urine bind to foam and fibres at a molecular level.

5. Spills and Accidents

Any liquid that soaks into a mattress (urine, coffee, beverages, vomit) can leave lasting odours if not cleaned thoroughly and immediately. The deeper the liquid penetrates, the harder it is to eliminate the smell.

6. Cigarette Smoke

Mattresses absorb airborne odours, and cigarette smoke is one of the most persistent. Smoke particles embed deep into foam layers and cannot be removed with surface cleaning alone.

How to Remove Mattress Odours

For Sweat, Body Odour, and General Mustiness

1. Strip all bedding and vacuum the entire mattress surface using the upholstery attachment.
2. Sprinkle a generous layer of baking soda across the entire surface. For stronger odours, add 5-10 drops of tea tree essential oil to the baking soda before applying (tea tree has natural antimicrobial properties).
3. Leave for 4 to 8 hours (or overnight if possible).
4. Vacuum thoroughly to remove all baking soda.
5. If odour persists, repeat the process on the other side of the mattress (if accessible).

For Urine or Liquid Stain Odours

1. Mix one cup of white vinegar with one cup of water in a spray bottle.
2. Spray the affected area until damp (not soaked).
3. Blot with clean towels to absorb moisture.
4. Sprinkle baking soda over the area and let it sit for 8 to 12 hours.
5. Vacuum thoroughly.
6. For persistent urine odours, use an enzyme-based cleaner (available at pet stores) which breaks down the proteins causing the smell.

For Mould Smell

If you suspect mould, do not attempt to treat the mattress yourself. Mould inside a mattress cannot be fully removed with surface cleaning. The spores penetrate deep into foam layers where they continue to grow. A mattress with confirmed mould growth should be replaced. See the section on mould below for more detail.

The Mould Problem in Canadian Homes

Canadian homes are particularly susceptible to mattress mould because of our climate patterns. During winter, cold exterior walls and windows create condensation points inside bedrooms. During summer, humidity levels in Ontario, Quebec, and the Maritimes can exceed 80%, creating ideal mould growth conditions.

Signs of Mould in Your Mattress

• Persistent musty or earthy smell that does not respond to cleaning
• Visible dark spots (black, green, or grey) on the mattress surface or sides
• Allergy symptoms that worsen at night (congestion, sneezing, itchy eyes)
• Damp or clammy feeling on the mattress surface

What Causes Mattress Mould in Canada

• Mattress on the floor: No airflow underneath traps moisture between the mattress and floor
• Basement bedrooms: Higher humidity and cooler temperatures promote condensation
• Solid platform beds without ventilation: Closed-bottom platforms restrict airflow
• No mattress protector: Sweat soaks directly into foam without a moisture barrier
• Lack of room ventilation: Closed windows during Canadian winters trap humidity indoors

How to Prevent Mattress Smells

1. Use a waterproof mattress protector from day one. This is the single most effective step. A good protector blocks sweat, spills, and body oils from reaching the mattress while remaining breathable.
2. Wash sheets weekly. Sheets absorb sweat and body oils first. Washing them weekly prevents transfer to the mattress.
3. Ensure airflow under the mattress. Use a bed frame with slats or a slatted platform. Never place a mattress directly on the floor long-term, especially in basements.
4. Ventilate your bedroom. Open windows when weather permits. Run a fan or dehumidifier in humid conditions. Target indoor humidity below 50%.
5. Vacuum the mattress every 3-6 months. Use the upholstery attachment to remove dust, dead skin, and dust mite accumulation.
6. Rotate your mattress regularly. Rotation distributes moisture absorption across the entire mattress surface.
7. Address spills immediately. Blot (do not rub) liquid spills immediately. Clean with appropriate solutions before the liquid soaks deep into the foam.

Certifications That Reduce Mattress Odour

If you are sensitive to chemical smells or buying a mattress for a child, look for these certifications:

• CertiPUR-US: Certifies that foam is made without ozone depleters, certain flame retardants, mercury, lead, formaldehyde, and certain phthalates. Limits total VOC emissions to less than 0.5 parts per million. Most major Canadian brands carry this certification.
• GREENGUARD Gold: Stricter than CertiPUR-US, this certification tests the finished product (not just the foam) for over 10,000 chemical compounds. Products must meet emission limits for use in schools and healthcare facilities.
• GOTS (Global Organic Textile Standard): Certifies organic materials and restricts chemical inputs at every stage of production. GOTS-certified mattresses have the lowest chemical odour.
• OEKO-TEX Standard 100: Tests for harmful substances in textiles and certifies that products are free of certain chemicals at levels that could harm health.

When Smell Means Replacement

Some mattress smells cannot be fixed. Replace your mattress if:

• You see or suspect mould growth (musty smell that persists after cleaning)
• The mattress has absorbed significant urine that soaked deep into the foam
• Cigarette smoke odour has permeated the materials
• The mattress is over 7-8 years old with persistent body odour despite cleaning
• You experience allergy symptoms (sneezing, congestion, itchy eyes) that improve when you sleep elsewhere

Visit Mattress Miracle at 441 West St, Brantford for a fresh start. Our Restonic mattresses are CertiPUR-US certified with low-VOC foam, and you can try them in our showroom where they have already off-gassed completely. Pair your new mattress with a waterproof protector from day one, and you will never deal with odour issues again. Call (519) 770-0001.

Frequently Asked Questions