Mothballs don’t work for mice, and using them this way is both ineffective and potentially illegal. While the idea has been passed around for decades, the naphthalene in mothballs is present in far too small a quantity to repel rodents, and the odor dissipates too quickly to have any lasting effect. Pest control experts and the EPA agree: mothballs are registered strictly for killing moths and their larvae in enclosed containers, not for deterring mice.
Why Mothballs Fail as Mouse Repellents
Mothballs work by slowly turning from a solid into a gas, a process called sublimation. That gas is what kills moths inside a sealed garment bag or storage chest. The two active chemicals used in U.S. mothballs, naphthalene and paradichlorobenzene, are present in high concentrations, but they need an enclosed space to build up to lethal levels for insects.
When you scatter mothballs in an attic, crawlspace, or along a wall, the chemical vapor disperses into the surrounding air almost immediately. Naphthalene breaks down in open air within about a day when exposed to moisture and sunlight. Even indoors, the concentration never gets high enough to bother a mouse. Mice can simply avoid the immediate area of the mothball and continue using other entry points. Orkin, one of the largest pest control companies in the U.S., states plainly that mothballs are ineffective as a rodent repellent.
Health Risks to You and Your Family
The bigger problem with scattering mothballs around your home is what the fumes do to people. A CDC report documented a case in Indiana where a woman, her four-year-old daughter, and seven relatives across multiple households all developed symptoms from extensive mothball use. Those symptoms included headaches, nausea, vomiting, abdominal pain, confusion, severe anemia, and kidney problems.
Inhaling naphthalene fumes can cause a surprisingly wide range of effects: skin and eye irritation, gastrointestinal distress, neurological symptoms like confusion and convulsions, and blood disorders that damage red blood cells. Children are especially vulnerable because of their smaller body weight and tendency to handle or even mouth small objects that look like candy. The risk increases dramatically when mothballs are used outside of sealed containers, because the fumes spread through living spaces rather than staying contained.
Risks to Pets
Dogs and cats face serious danger from mothballs. According to the Merck Veterinary Manual, pets can be poisoned not just by eating mothballs but also by inhaling the fumes or absorbing the chemicals through their skin. Naphthalene exposure in animals typically starts with vomiting and loss of appetite, then can progress to a condition where red blood cells break down, causing pale gums, difficulty breathing, and in rare cases, tremors and seizures. Paradichlorobenzene causes similar gastrointestinal distress along with potential liver and kidney damage from repeated exposure.
It Violates Federal Pesticide Law
Mothballs are EPA-registered pesticide products, which means they come with a legally binding label. That label specifies use in enclosed containers for moth control only. Using them in any other way, such as tossing them in your yard, attic, or crawlspace to repel mice, violates federal law. The EPA requires approval of all pesticide labels before products can be sold and takes enforcement action against misuse. This isn’t a technicality: the label restrictions exist specifically because the chemicals are toxic enough to harm people and the environment when used improperly.
When mothballs are placed outdoors or in unsealed areas, naphthalene can pass through sandy soil into groundwater. While microorganisms in soil break down most naphthalene within one to three months, the chemical can dissolve in water and potentially reach drinking water sources near landfills or areas of heavy use.
What Actually Works for Mice
The CDC recommends a straightforward three-part approach to mouse control: remove food sources, eliminate shelter, and seal entry points. This strategy, called exclusion, is far more effective than any repellent because it addresses why mice are in your home in the first place.
Start by finding and sealing holes. Mice can squeeze through gaps as small as a dime. Check where pipes and wires enter your home, around door frames, along the foundation, and near vents. Steel wool stuffed into small gaps works well because mice can’t chew through it. For larger openings, use metal flashing or hardware cloth secured with caulk.
Next, cut off their food supply. Store dry goods like cereal, rice, and pet food in hard plastic or glass containers with tight lids. Clean up crumbs and spills promptly, and don’t leave pet food bowls out overnight. Take garbage out regularly and use bins with secure lids.
For active infestations, snap traps remain one of the most reliable options. Place them along walls where you’ve noticed droppings, with the trigger end facing the wall. Peanut butter works well as bait because mice have to engage with the trap to eat it rather than snatching a piece of food and running. If the infestation is large or persistent, a licensed pest control professional can assess entry points you may have missed and develop a targeted plan.
Reducing clutter in storage areas like garages, basements, and attics also helps by eliminating nesting material. Mice build nests from shredded paper, fabric, insulation, and other soft materials, so keeping these areas organized and using sealed plastic bins instead of cardboard boxes makes your home less inviting.