Most Likely Causes (Ranked)
Mothballs (naphthalene or paradichlorobenzene) slowly sublimate from solid to gas. If a previous occupant placed them in closets, attics, walls, crawl spaces, or between walls for pest control, they can continue off-gassing for years. Even after the mothball dissolves completely, residue absorbed into wood and fabrics continues to release the smell.
Some older pest control products — particularly those for termites, carpenter ants, and moths — contain naphthalene or paradichlorobenzene. These chemicals were sometimes applied in wall cavities, under floors, or in crawl spaces. Modern pest control rarely uses these chemicals, so this is primarily an issue in older treatments.
Some older roofing materials, driveway sealants, and waterproofing products contain coal tar, which releases naphthalene. If your home has a coal tar-based roof or foundation coating, warming temperatures can increase off-gassing.
Some toilet deodorizer blocks and drain fresheners contain paradichlorobenzene — the same chemical in some mothballs. If someone is using these products, they can make the whole bathroom or adjacent rooms smell like mothballs.
How to Fix It
Find and Remove the Source
$0Essential first step.
- 1Search closets, attics, crawl spaces, under sinks, and storage areas for actual mothballs or moth cakes.
- 2Check behind drawers, on closet shelves, and in corners of cabinets — mothballs roll into forgotten spaces.
- 3Remove any mothballs found. Dispose of them in a sealed bag in outdoor trash — don't flush them.
- 4Check toilet bowls and drains for deodorizer blocks containing paradichlorobenzene.
Ventilate and Air Out
$0Critical for clearing residual naphthalene.
- 1Open all windows and run fans to create cross-ventilation.
- 2Open closets, cabinets, and storage spaces while airing out.
- 3This process may take days to weeks for heavily contaminated spaces.
- 4Run an air purifier with activated carbon filter — carbon adsorbs naphthalene effectively.
Clean Contaminated Surfaces
$20-100Remove absorbed naphthalene from materials.
- 1Wash all clothing, linens, and fabric items that smell of mothballs — use vinegar in the wash cycle.
- 2Wipe down closet shelves, walls, and floors with a vinegar and water solution (50/50).
- 3For wood surfaces heavily saturated with mothball odor, sand lightly and seal with shellac-based primer (Zinsser BIN).
- 4Place bowls of activated charcoal or baking soda in affected areas to absorb residual odor.
Professional Remediation
$300-2,000For severe contamination, especially in walls or crawl spaces.
- 1Call an indoor air quality specialist or environmental remediation company.
- 2They can test naphthalene levels in your air to determine severity.
- 3Remediation may involve removing contaminated insulation, sealing surfaces, or ozone treatment.
- 4If the source is in wall cavities, they may need to access and clean inside the walls.
When to Call a Professional
Chronic naphthalene exposure is linked to hemolytic anemia and liver damage — take this smell seriously
Children and pets are most vulnerable to naphthalene toxicity — don't use mothballs in accessible areas
Mothballs are pesticides regulated by the EPA — using them in ways not directed on the label is illegal
If anyone in the household has headaches, nausea, or fatigue coinciding with the smell, see a doctor and address the source urgently
How to Prevent It
Use cedar blocks or lavender sachets instead of mothballs — effective and non-toxic moth deterrents.
Store seasonal clothing in sealed bags or bins rather than relying on mothballs.
When buying a home, check for mothball smell during the inspection — it's expensive to remediate.
Maintain good ventilation in closets and storage areas — airflow prevents moth infestations naturally.
Why Mothball Smell Persists So Long
Mothballs work through sublimation — the solid slowly converts directly to gas. A single mothball can take 3-6 months to fully sublimate, and during that time, the naphthalene gas is being absorbed into every porous surface nearby: wood, fabric, drywall, carpet, and insulation.
Even after the mothball is gone, these materials slowly release absorbed naphthalene for months to years. Wood is especially problematic because naphthalene penetrates deep into the grain. In enclosed spaces like closets and wall cavities with poor ventilation, the smell can persist for a decade or more.
Naphthalene is classified as a possible carcinogen (Group 2B) by the International Agency for Research on Cancer. Short-term exposure at household levels is unlikely to cause serious harm, but chronic exposure — living in a house that consistently smells of mothballs — warrants remediation. The EPA recommends removing the source and improving ventilation as the primary response.
Frequently Asked Questions
Chronic exposure to naphthalene can cause headaches, nausea, and in severe cases hemolytic anemia. Short-term exposure at typical household levels is low risk, but the source should be found and removed, and the space ventilated.
Without intervention, months to years — especially in enclosed spaces. With active removal, cleaning, and ventilation, you can eliminate it in 1-4 weeks for mild cases.
No — masking doesn't reduce your exposure to naphthalene. Find and remove the source, ventilate, and clean contaminated surfaces.
Yes. Cedar blocks, lavender sachets, and sealed garment bags are effective moth deterrents without toxic chemicals. Keeping clothes clean before storage also helps — moths are attracted to human oils and food stains on fabric.
The source may be hidden — in wall cavities, under insulation, in crawl spaces, or absorbed into building materials from past use. Old pest control chemicals and coal tar-based products can also smell like mothballs.