A single mothball typically lasts anywhere from two to six months in a sealed container, though the actual timeline depends heavily on temperature, airflow, and how tightly sealed the storage space is. In open air, a standard mothball can disappear in as little as a few weeks.
How Mothballs Break Down
Mothballs don’t melt or evaporate like water. They undergo sublimation, meaning they transition directly from a solid into a gas without ever becoming liquid. This is the same process that makes dry ice “smoke.” As the mothball releases fumes, it slowly shrinks until nothing is left. Those fumes are the active pesticide, either naphthalene or paradichlorobenzene, and they’re what actually kills moths and fabric pests.
The rate of sublimation is not perfectly steady. Research on naphthalene spheres shows that mass loss fluctuates with changes in surrounding airflow, even small disturbances like opening a door or running an HVAC system. Humidity, on the other hand, has a negligible effect on how quickly a mothball shrinks.
What Makes Them Last Longer or Shorter
The single biggest factor is whether the container is sealed. In an airtight bin or garment bag, mothball fumes build up in the enclosed air until the concentration reaches a point where sublimation slows down dramatically. The surrounding air essentially becomes saturated with vapor, and the mothball can’t release gas as quickly. This is exactly what you want for pest control: a high concentration of fumes trapped around your clothing for months. In these conditions, mothballs commonly last three to six months, sometimes longer.
In an open or poorly sealed space, fresh air constantly replaces the vapor around the mothball, preventing saturation and allowing sublimation to continue at full speed. A mothball left in a well-ventilated room, a closet with gaps, or outdoors can shrink noticeably within days and disappear entirely in two to four weeks. Higher temperatures also speed up the process, since warmth increases vapor pressure at the surface of the ball and accelerates gas release.
Size matters too. Larger mothballs and blocks take longer to fully sublimate than small ones simply because there’s more material to work through. Some products are sold as chunks or cakes specifically to extend their effective life in storage.
How Long the Smell Sticks Around
The mothball itself may be gone long before its smell is. Naphthalene and paradichlorobenzene vapors embed themselves into fabrics, wood grain, and porous surfaces, and getting rid of that odor is often a bigger challenge than the mothball’s actual lifespan.
On clothing, the smell can last from a few days to several weeks after you remove the garments from storage. Thin cotton shirts tend to air out faster, while thick fabrics like wool coats, heavy sweaters, blankets, and vintage garments hold the odor much longer. A light smell from short-term storage may clear up after fresh air and a single wash. A strong odor from months of storage often needs repeated cycles of airing, soaking, and washing.
Furniture is even more stubborn. Mothball chemicals can embed deep into wood grain, and the odor may persist for weeks even with active efforts to remove it. Getting the wood wet with plain water can actually make things worse by driving the smell deeper into the material.
Getting Rid of Lingering Odor
For clothing, start by hanging garments outdoors in fresh air and sunlight for at least a full day before washing. Sunlight and airflow do more initial work than detergent alone. If the smell remains after one wash, try soaking the clothing in a solution with white vinegar or baking soda before washing again. Repeat as needed for heavily saturated items.
For furniture, ventilation and gentle heat are your best tools. Place the piece near an open window with a fan blowing air across it and out the window. Using a blow dryer on the wood surfaces once a day can help, since direct heat accelerates the release of trapped vapors. Avoid scrubbing with water. Overnight, close drawers with natural odor absorbers inside: open boxes of baking soda, charcoal briquettes, coffee grounds, bowls of white vinegar, or newspaper sprinkled with essential oils. Activated charcoal works particularly well. Light sanding can help on unfinished or inconspicuous surfaces by physically removing the top layer of contaminated wood.
Safety and Proper Use
Mothballs are registered pesticides regulated by the EPA, and their labels carry legal weight. They are designed exclusively for use inside airtight containers to protect stored fabrics. Using them in unsealed closets, attics, crawl spaces, or outdoors is both illegal and hazardous, because the toxic fumes then accumulate in living spaces where people and pets breathe them in over extended periods.
One of the most common misuses is scattering mothballs in gardens or around foundations to repel snakes, rodents, or insects. This doesn’t work well and introduces toxic chemicals into soil, water, and areas where children and animals play. Some mothballs sold online or in informal markets are illegal imports that haven’t been evaluated for safety, so their chemical contents and concentration are unknown.
If you’re using mothballs as intended, place them in a sealed plastic bin or vacuum-sealed garment bag with the clothing you want to protect. Keep the container in a space away from living areas, and don’t open it more than necessary. When you retrieve your clothes, air them out thoroughly outdoors before wearing or storing them in your closet. The fumes are the entire point of the product, but they should never be part of the air you breathe regularly.