Mothballs show up in a lot of pest advice passed down through families, tucked into attics, sprinkled in gardens, or left in sheds to keep everything from mice to snakes away. Most of that advice is wrong, and using mothballs outside their intended purpose can actually be a health hazard.
What They’re Actually For
Mothballs are a pesticide, typically made of naphthalene or paradichlorobenzene, designed to kill clothing moth larvae and their eggs in an airtight, sealed container. The label instructions on every legitimate product specify that they must be used in a sealed container, which is the part almost everyone skips. Loose mothballs tossed into an open attic or under a porch aren’t doing the job they’re built for, since the fumes that kill moth larvae need to be concentrated in an enclosed space to work. In a properly sealed storage container, the fumes build up to a concentration strong enough to kill larvae and eggs over time. In an open attic, those same fumes disperse into a much larger volume of air and never reach that concentration, which means the moths aren’t being controlled and the fumes are just leaking into your living space instead.
Why They Don’t Work as a General Repellent
The idea that mothballs repel mice, snakes, squirrels, or other pests is one of the most persistent pieces of pest control folklore around, and it doesn’t hold up. Studies on this haven’t found reliable evidence that open-air mothball use deters rodents or snakes in any meaningful way. Animals may avoid the immediate area around a strong smell for a short time, but they habituate to it quickly, and the fumes dissipate outdoors long before they reach a concentration that would do anything at all. This idea likely persists because naphthalene’s smell is unmistakable and unpleasant to humans, so it seems logical that it would repel animals too. Rodents and snakes rely far more on scent trails, food sources, and shelter than on avoiding a strong odor, which is why mothballs scattered around a garden bed or under a deck rarely change animal behavior in any lasting way.
The Health Risk Side
- Naphthalene fumes are toxic when inhaled in enclosed, poorly ventilated spaces like attics, crawlspaces, and sheds, and can cause headaches, nausea, and more serious effects with prolonged exposure.
- Mothballs are especially dangerous around pets, since dogs and cats are sometimes drawn to the smell and can suffer serious poisoning if one is swallowed.
- Children are also at risk, since mothballs can resemble candy and are small enough to be a swallowing hazard beyond the chemical exposure itself.
- Using mothballs outdoors, in gardens, or scattered in ways not specified on the label is against the label instructions in most jurisdictions, since pesticide labels are legally binding on how the product can be applied.
- Prolonged exposure in a home with mothballs used incorrectly has been linked to more serious health effects over time, particularly in poorly ventilated spaces where fumes accumulate.
The Regulatory Side of Mothball Misuse
Mothballs are registered pesticides, which means their label carries legal weight beyond a manufacturer’s suggestion. Using a product in a way that contradicts its label, scattering mothballs loose in a garden bed or open attic when the label specifies a sealed container, is a violation of pesticide law in most jurisdictions, not just a case of reduced effectiveness. This is worth knowing because it applies to plenty of other common household products too, and it’s part of why reading the actual label matters more than following advice passed down secondhand. The CDC’s National Institute for Occupational Safety and Health publishes guidance on safe naphthalene exposure limits that’s worth a look for anyone dealing with a home that’s had mothballs used incorrectly for years.
Why the Smell Lingers So Long
Naphthalene sublimates, meaning it moves directly from a solid to a gas without passing through a liquid stage, which is exactly why a mothball placed in an attic slowly disappears over months while releasing fumes the entire time. That same property is why the smell can linger in a house for months or even years after the mothballs themselves are removed, since fumes soak into porous materials like wood, drywall, and insulation and continue off-gassing slowly afterward. Ventilating a space after removing mothballs helps, but a heavily contaminated area, insulation in particular, sometimes needs to be replaced rather than aired out if the smell doesn’t fade within a few weeks. This is one more reason the sealed-container rule exists in the first place: it’s not just about pest control effectiveness, it’s about keeping the fumes contained to a space that isn’t shared with the rest of a home’s air.
A More Effective Approach to Attic and Shed Pests
If mothballs were being used in an attic or shed hoping to deter rodents specifically, the more effective approach addresses the same three things that matter for any rodent problem: entry points, food, and shelter. Steel wool or hardware cloth packed into gaps around soffits and eaves blocks entry in a way scent never could, since rodents can chew through most other materials but not steel wool. Removing stored cardboard, fabric, and paper clutter takes away nesting material, and keeping stored food, including pet food and birdseed, in sealed metal or heavy plastic containers removes the food incentive entirely. Combined, these three steps do more in a single afternoon than a bag of mothballs would do in a year, without any of the fume exposure risk.
Where the Folklore Around Mothballs Started
The idea that mothballs repel a wide range of animals likely dates back generations, to a time before better rodent and wildlife exclusion products were widely available and homeowners reached for whatever strong-smelling household item was on hand. Naphthalene’s distinctive smell made it an obvious candidate to try on anything unwelcome, from squirrels in an attic to snakes near a woodpile, and enough people repeating the same advice over enough decades gave it a credibility it never earned scientifically. The same pattern shows up with other strong-smelling folk remedies passed between neighbors and family members, and it’s worth applying a bit of healthy skepticism to any pest advice that relies entirely on a product’s smell rather than addressing the food, water, or shelter that’s actually drawing an animal in.
Retailers and online marketplaces are also required to follow these label restrictions when listing a pesticide product, though enforcement is inconsistent, and it’s not unusual to see mothballs discussed or sold online in ways that directly contradict the label’s own instructions.
Other Pest Myths Worth Retiring
Mothballs aren’t the only piece of hand-me-down pest advice that doesn’t hold up. Dryer sheets in gardens or vents, bright lights left on to deter rodents, and ultrasonic pest repellers marketed for home use all share the same problem: they might have a short-term, localized effect at best, and none of them address why pests are actually present. The pattern across most of these myths is the same one that makes mothballs so persistent: something faintly unpleasant to a person gets assumed to be equally unpleasant, or worse, to an animal with completely different senses and priorities.
What to Use Instead
For actual clothing moth prevention, cedar blocks and airtight storage containers do the job without the fumes. Cedar’s effectiveness fades over time as the oils dry out, so blocks or chips need occasional sanding or replacing to stay useful, while a sealed plastic bin with a good gasket works indefinitely without any upkeep. For rodent or snake deterrence, the more effective approach is removing what’s attracting them in the first place, sealing entry points, and clearing brush or clutter that gives them cover, paired with targeted treatment where activity is confirmed.
If You’ve Already Used Mothballs Incorrectly
If mothballs have been scattered loose in an attic, shed, or garden, the fix is straightforward: put on gloves, collect them, and dispose of them according to your local household hazardous waste guidelines rather than in regular trash. Ventilate the space afterward, since residual fumes can linger for a while in an enclosed area.
A Few Common Questions
Can mothballs be used in a closet with the door kept shut? A closet that stays closed most of the time comes closer to the sealed-container requirement than an open attic, but it’s still not a truly airtight space, and fumes can seep out under a door over time. A sealed garment bag or bin inside the closet is a safer approach.
Do mothballs work on other fabric pests, like carpet beetles? No. Mothballs are labeled specifically for clothing moths. Carpet beetle larvae respond to a different set of controls, including vacuuming, steam cleaning, and targeted treatment of infested material, and mothballs aren’t an effective substitute.
Is there a safer alternative that still uses a similar chemical approach? Some pheromone-based moth traps target adult moths specifically and avoid the broad fume exposure of naphthalene altogether, which is a reasonable option for anyone who wants an active measure without the ventilation concerns.
If you’re dealing with a rodent or wildlife issue mothballs haven’t solved, a pest professional’s inspection will usually find the real cause faster than any home remedy will.
