Published by BuzzSkito Mosquito & Tick Control
Published October 7, 2026 · Drafted with AI assistance and fact-checked against the sources listed below
Do mothballs keep mice away?
No. Mothballs do not keep mice away in any reliable way. The National Pesticide Information Center (NPIC), a pesticide information service run under a cooperative agreement between Oregon State University and the US Environmental Protection Agency (EPA), says mothballs have little or no effect as repellents and are not meant to be used as animal repellents. The center's mothball infographic is blunter: mothballs are meant to kill clothing insects, and they do not repel animals.
The guidance written for mice agrees. NC State Extension's guide to mice in buildings lists moth balls with peppermint oil and ammonia, accepts that there is some evidence certain odors can repel mice, and still concludes that repellents are not a reliable form of mouse management or prevention. Mothball makers do not claim otherwise, according to an Oregon State University Extension publication on mothballs, which notes that manufacturers do not claim these products are effective for anything but the control of moths, or carpet beetles in the case of some products.
There is a kernel behind the idea. NPIC's own naphthalene fact sheet, last reviewed in 2010, says the gas may repel animals and that the odor is thought to be unpleasant enough to drive animals away in repellent products. That is a long way from evidence that a box of mothballs clears a house. None of the sources behind this page reports a trial in which mothballs ended a mouse problem, and none gives an amount of mothballs to use against mice. The complete guide to mice in US homes sets out the methods that do have support, and the overview of mouse repellents by type shows where mothballs sit among the scent and sound products.
Why don't mothballs work on mice?
None of the sources tests the reason directly, but the design of the product points to one: mothballs are fumigants made to work where their vapor is trapped, and a house is not an airtight container. NPIC explains that the chemicals turn into gases that build up inside airtight containers, killing clothes moths and their eggs. EPA's 2008 reregistration decision for naphthalene adds that labels for indoor moth treatment recommend keeping the product in an airtight space for a minimum of seven days, and that labels specify treated indoor areas should be airtight to be effective.
Put the same mothballs on an attic floor, in a garage or along a foundation and the vapor has nowhere to build. NPIC says that when mothballs are used out in the open, the gas is released into the environment where people can breathe it. EPA's review makes a related point about the naphthalene flakes and granules that were registered as animal repellents: re-treatment was recommended as needed to maintain odor intensity, and hot weather, wind and rain could diminish the product's effectiveness.
Your own nose is a poor gauge of whether any of this is working. Oregon State says people can detect the odor of mothballs at a few parts per billion in the air, and compares one part per billion to several drops of water in an Olympic-size swimming pool. A smell that seems overpowering to you tells you the vapor has reached the rooms you live in. It tells you nothing about the mice.
Would more mothballs work?
None of the sources used here gives an amount of mothballs that drives mice out, and adding more adds vapor to the air in the house. Oregon State uses the example of mothballs placed in an attic to repel squirrels. It calls that a misapplication that may cause a noxious odor throughout the home, and says family members may experience adverse health effects or even have to leave. That is where the more-is-better road ends in these sources: with a house the people may have to leave. None of them describes a house the mice left.
Will mothballs kill mice?
None of the sources says they do, and EPA's figures suggest the vapor in a home falls well short of harming a rodent. EPA did not assess mothballs as a mouse killer. In its 2008 review of risks to people, the agency estimated that acute and short-term naphthalene exposures in residences were 20 and 30 times, respectively, below the dose that produced no adverse effects in laboratory rodents. Those estimates drew on an exposure study in which mothballs were placed in a closet and a dresser, not in an attic scattered with them, so they are a guide and not a measurement of misuse.
EPA's review lists naphthalene's pesticide type as insecticide and repellent; rodenticide is not on that list. The products that are rodenticides, and the EPA rules on how consumers may use them, are covered in the guide to mouse poison.
What are mothballs, and what does the label allow?
Mothballs are pesticides, and their labels direct them into airtight containers with stored fabric. NPIC describes today's mothballs as typically almost 100 percent active ingredient, either naphthalene or paradichlorobenzene. Oregon State classes both as fumigants, meaning their volatile chemicals vaporize at lower temperatures such as room temperature, and notes that the same chemicals are also sold for clothes moths as cakes, crystals, tablets, bars and flakes. Its instruction on use is short: mothballs must be used in an airtight space, such as a garment bag or a well-sealed container.
EPA's review traces the first naphthalene pesticide registration to 1948 and describes the indoor moth products as registered to kill moths inside airtight spaces, giving closets, chests and garment bags as examples. About 7.5 million pounds of naphthalene were marketed as a pesticide in an average year at that time, the vast majority in indoor moth products. Nothing in that labeled use involves open rooms, vehicles or soil, which is where people put mothballs when the target is a mouse.
| Where the mothballs go | On a mothball label? | What the sources say |
|---|---|---|
| Sealed garment bag or airtight storage container with clothing | Yes | The labeled use. The trapped vapor kills clothes moths, and NPIC rates the exposure risk for people and pets as low when mothballs are used properly this way. |
| Attic, wall void or crawl space | No | Oregon State says mothballs should not be used in any of the three, and that attic use may send a noxious odor through the home. |
| Car, truck, RV or other vehicle | No | Oregon State lists vehicles among the places mothballs should not be used, and NPIC warns against using them as repellents in vehicles. |
| Garden or yard | No | Oregon State lists gardens and NPIC lists yards. NPIC warns that mothballs used incorrectly as repellents may harm wildlife, pets or people. |
| Trash cans | No | Named by Oregon State as a place mothballs should not be used. |
Sources: National Pesticide Information Center; Oregon State University Extension, PNW 606.
Is it illegal to use mothballs for mice?
Yes, unless the label of the product in your hand lists that use, and the labels on mothballs sold for clothes storage do not. Oregon State puts it this way: because mothballs are registered pesticides, it is illegal to use them in locations that are not on the label. Its list of the pests people misuse mothballs against includes mice and rats, along with squirrels, skunks, deer, raccoons, moles, snakes and pigeons, and it says any such use is illegal. NPIC's infographic makes the general point that following the directions on the package is required by law.
NPIC's answer to whether mothballs can be used to repel insects or animals is the working rule: no, not unless the label describes that type of use. So read the label before anything else. If it talks only about clothes moths and airtight storage, the attic, the garage and the car are off the table.
Are any naphthalene products labeled for animals?
Some have been, and they are not the mothballs sold for closets. EPA's 2008 review counted nine registered naphthalene products, eight of them for end users. Besides the moth products, it describes products registered to repel bats, tree squirrels and birds from attics and wall voids, and outdoor products registered to repel rabbits, snakes, Norway rats, roof rats and house mice. The repellents were flakes or granules, and the outdoor ones were applied in a band around ornamental plants, planting beds, gardens or building perimeters.
Two cautions apply. That list is a snapshot from 2008, and this page did not confirm which of those products remain registered or what their labels say today. EPA's document is also a risk assessment; it does not report how well the repellents performed against mice. A product whose label names house mice and a place of use can be used there as the label directs. A box of closet mothballs cannot borrow that label.
Are mothball fumes harmful to people and pets?
They can be, and the smell is the pesticide: NPIC's infographic says that if you smell mothballs, you are breathing in the pesticide vapor. NPIC says exposure to the gas can lead to headaches, nausea and irritation of the eyes and nose, and that longer-term exposure can cause more serious effects such as liver and kidney damage. Oregon State describes paradichlorobenzene as a potential hazard too, though typically less so than naphthalene.
The risk depends heavily on how the product is used. NPIC says the exposure risk for people and pets is low when mothballs are used properly inside airtight containers, and EPA concluded in 2008 that its inhalation estimates for homes did not represent a risk of concern. Using mothballs against mice means doing the opposite of what those findings assume: leaving them loose, in the open, often in large numbers.
| Exposure | What the sources report |
|---|---|
| Breathing the vapor | Headaches, nausea, vomiting, diarrhea, eye and nose irritation and coughing (NPIC); for naphthalene, Oregon State also lists dizziness and difficulty breathing |
| Breathing it over a longer period | More serious effects such as liver and kidney damage |
| A child swallowing a naphthalene mothball | Damage to red blood cells (hemolytic anemia); NPIC also reports diarrhea, fever, abdominal pain and painful urination with discolored urine in small children |
| An infant wearing clothing, diapers or blankets stored with mothballs and not washed afterward | Anemia |
| A dog eating naphthalene mothballs | Lethargy, vomiting, diarrhea, lack of appetite and tremors |
Sources: NPIC mothball FAQ and naphthalene fact sheet; Oregon State University Extension, PNW 606.
A serious effect NPIC links to naphthalene is hemolytic anemia, in which red blood cells break apart and stop carrying oxygen the way they should. NPIC says it might develop after breathing in enough of the vapor or eating a naphthalene mothball, and that people with an inherited enzyme deficiency are at much greater risk of it than people with normal enzyme levels. NPIC also reports that EPA has classified naphthalene as a possible human carcinogen on the basis of animal studies, and that the International Agency for Research on Cancer rates it as possibly carcinogenic to humans.
Why are children the main concern?
Children are the main concern because, in EPA's incident data, they are the ones who find mothballs and swallow them. In the reports EPA reviewed, poison control centers logged an average of about 1,647 naphthalene exposures a year from 1993 to 2005, and the large majority of incidents in children under 6 came from swallowing mothball products used indoors. A toddler swallowing a mothball was the only scenario in the whole assessment that EPA found to be of concern, and the agency calculated that the amount meeting its target margin of exposure was less than 1 percent of a single mothball.
The sources differ in emphasis on how bad one mothball is. Oregon State says eating just one naphthalene mothball can damage a young child's red blood cells. EPA's review of the poison control data found that about 7 percent of naphthalene incidents in children produced any symptoms and fewer than 1 percent produced moderate or major ones. Both lead to the same rule, which EPA required on labels: keep the product out of reach of children and do not place it in areas accessible to them.
The 2008 decision went further. It required that naphthalene no longer be formulated into loose mothballs after September 30, 2013, unless they are enclosed in sachets, and that moth cakes and blocks measure at least 2.5 inches across. Mothballs tipped out along a baseboard or a garage floor are the loose, reachable product those rules were written to end.
What about dogs and cats?
Pets can be harmed too. NPIC's infographic warns that kids and pets might think mothballs are food or candy. The symptoms in the table above are the ones NPIC's fact sheet gives for dogs. The sources used here give none for cats, so cat owners should ask a veterinarian instead of assuming the same picture applies.
What should you do if mothballs are already out?
Pick them up, seal them in an airtight container for disposal, and air out the space if the smell is still there. That is the cleanup NPIC's infographic gives for misused mothballs. The steps below come from the infographic, except the fourth, which follows from a finding in NPIC's naphthalene fact sheet:
- Collect the mothballs and store them in an airtight container for disposal.
- Ventilate the area if the smell is still present.
- Follow the disposal instructions on the product label, or contact your local household hazardous waste program.
- Wash clothing, diapers and blankets that were stored with mothballs before an infant wears or uses them. NPIC's fact sheet reports anemia in infants who wore clothing, diapers or blankets that had been stored in mothballs and not washed afterward.
- Call NPIC at 800-858-7378 if you want more information.
The smell can linger after the mothballs are gone. Oregon State warns that once the vapors enter a home, the odor can persist for a long time. Outdoors, NPIC's fact sheet says the half-life of naphthalene may range from less than one day in air to more than 80 days in soil, so naphthalene that ends up bound to soil can last far longer than naphthalene in the air. Mouse droppings and nesting material need a careful cleanup of their own, and the method is in the guide to removing mice and cleaning up after them.
What works instead of mothballs?
Closing the holes mice use and trapping the mice already inside. NC State Extension's guide covers the signs of an infestation, monitoring, trapping, exclusion and chemical control. The opening that matters is small: NC State says a hole of 1/4 inch or larger will admit an adult mouse.
- Seal the outside. Push metal mesh into gaps, or pack them with size 00 steel wool or copper mesh and caulk over it. NC State notes that steel wool rusts and is flammable, and that expanding foam is not recommended because mice may chew through it. The guide to steel wool for mice covers which filler suits which gap.
- Fix the doors and vents. NC State calls for metal kick plates, metal thresholds and rodent-proof door sweeps on exterior doors, leaving no more than 1/4 inch of clearance between door and floor. Attic and crawl-space openings should have tight doors and screened vents, or be screened with 1/4-inch-mesh hardware cloth. A garage door has its own weak points, covered in the guide to mouse-proofing a garage door seal.
- Seal the inside. Seal holes, gaps and cracks in walls, floors, ceilings and cupboards, and the gaps around pipes, wires, conduits and ducts. NC State says caulk, plaster or paint may be needed to finish the repair.
- Trap. NC State says snap traps can be baited with food items, with peanut butter or honey used to stick the food to the trigger, and suggests baiting some traps with cotton balls or a ball of string because pregnant females scavenge for nest material. Set traps along mouse runways or where you see activity, do not use them where children or pets can reach them, and check them daily if possible. The guide to mouse traps compares the trap types and how to place them.
- Be careful with poison. NC State says rodenticides are best handled by pest management professionals, and that anyone using consumer baits should follow all label instructions and keep the bait in secure containers, in spots away from pets and children.
A vehicle is its own problem. How to keep mice out of a car deals with the engine bay, the wiring and the cabin.
Do other smells work better than mothballs?
Not reliably. NC State groups peppermint oil, moth balls, ammonia and the commercial mixes built from them together and gives them one verdict: not a reliable form of mouse management or prevention. It adds two practical problems with the plant oils. Highly volatile oils disappear quickly once they are out in the environment, and they may compromise the efficacy of the baits and traps you have set.
Each option has its own page. What smells mice are said to hate rates peppermint, ammonia, vinegar, cayenne and the rest one by one. Peppermint oil for mice looks at the most popular of them, and the explainer on the Vamoose mouse repellent looks at one branded scent product. Plug-in sound devices have a record of their own, summed up in the review of whether ultrasonic repellers work.
This guide is general educational information, not medical advice. If you have symptoms or concerns after a bite or exposure, contact a healthcare provider.
Use any pesticide exactly as its label directs. The label is the law, and what is registered and sold varies by state.
Frequently Asked Questions
Will mothballs kill mice?+
None of the sources used for this guide says they do. EPA did not assess mothballs as a mouse killer, but its 2008 review of naphthalene estimated that acute and short-term exposures in residences were 20 and 30 times below the dose that caused no adverse effects in laboratory rodents. EPA lists naphthalene's pesticide type as insecticide and repellent, and mothballs are made to kill clothes moths inside airtight containers. Scattering more of them adds vapor to the air that the people and pets in the building breathe.
Can I put mothballs in my car, RV or camper to keep mice out?+
No. Oregon State University Extension lists vehicles among the places mothballs should not be used, together with attics, wall voids, crawl spaces, gardens and trash cans, and the National Pesticide Information Center warns against using them as repellents in vehicles. The center also rates mothballs as having little or no effect as repellents. If the smell is already in a vehicle, its cleanup advice is to collect the mothballs in an airtight container for disposal and ventilate the space.
Is it legal to put mothballs in an attic or crawl space?+
Not with mothballs sold for clothes storage. Oregon State University Extension says mothballs should not be used inside attics, wall voids or crawl spaces, and that because they are registered pesticides it is illegal to use them in locations that are not on the label. It describes mothballs placed in an attic to repel squirrels as a misapplication that may spread a noxious odor through the home. The National Pesticide Information Center's rule is that mothballs cannot be used to repel animals unless the label describes that use.
How long does the smell of mothballs last?+
None of the sources used for this guide gives a number of days for a house. Oregon State University Extension says only that once the vapors enter a home, the odor can persist for a long time, and that people can detect it at a few parts per billion. The National Pesticide Information Center advises collecting misused mothballs in an airtight container and ventilating the area if the smell is still present. Outdoors, its naphthalene fact sheet gives a half-life from less than one day in air to more than 80 days in soil.
Are mothballs dangerous to dogs?+
They can be. The National Pesticide Information Center says dogs that have eaten naphthalene mothballs may have lethargy, vomiting, diarrhea, lack of appetite and tremors, and warns that pets might think mothballs are food. Its guidance is to contact your veterinarian, ASPCA Animal Poison Control at 888-426-4435 or Pet Poison Helpline at 855-764-7661 if a pet ate a mothball or has symptoms; a consultation fee may apply. Mothballs scattered on a floor or in a yard for mice are within a dog's reach in a way that mothballs sealed in a storage container are not.
Do mothballs keep rats, squirrels or snakes away?+
The National Pesticide Information Center gives one answer for all animals: mothballs have little or no effect as repellents and are not meant to be used as animal repellents. Oregon State University Extension lists rats, squirrels and snakes among the animals mothballs are illegally misused against. EPA's 2008 review does describe separate naphthalene flake and granule products that were registered to repel certain animals, including tree squirrels in attics and snakes, rabbits and rats outdoors, but those carried their own labels and are different products from closet mothballs.
Sources
- Can I use mothballs to repel insects or animals? — National Pesticide Information Center (Oregon State University and US EPA)
- What are mothballs? (mothball infographic) — National Pesticide Information Center (Oregon State University and US EPA)
- Naphthalene Fact Sheet — National Pesticide Information Center (Oregon State University and US EPA)
- Reregistration Eligibility Decision for Naphthalene (EPA 738-R-07-010, September 12, 2008) — US Environmental Protection Agency
- Mothballs: Proper use and alternative controls for clothes moths (PNW 606) — Oregon State University Extension Service (Pacific Northwest Extension publication)
- Surveillance and Management of Common Structure-Invading Mice — NC State Extension
How this guide was made: it was researched and drafted with AI assistance from the sources listed above. A second, independent AI pass then checked each factual claim against those sources. Found an error? Email support@buzzskito.ca.