Mothballs do not effectively repel mice. While the strong smell of mothballs might seem like it would drive rodents away, the concentration of active chemicals in a standard mothball is far too low to deter mice in any meaningful way. Beyond being ineffective, using mothballs for rodent control is actually illegal in the United States because it violates federal pesticide labeling laws.
Why Mothballs Don’t Work on Mice
Mothballs contain naphthalene or paradichlorobenzene, chemicals that slowly convert from a solid into a toxic vapor. That vapor is what produces the distinctive smell. Some people assume this strong odor will overwhelm a mouse’s sensitive nose and force it to leave. In practice, the amount of naphthalene in a single mothball is minimal, and repelling mice would require concentrations far higher than what any consumer product delivers.
Mice are also adaptable. Even if the smell near a nest or entry point bothered them initially, they would simply find a route around the mothballs. Scattering more mothballs to cover a larger area only increases the chemical exposure to everyone living in the home without making the space any less hospitable to rodents.
It’s Illegal to Use Mothballs This Way
Mothballs are registered pesticides regulated by the Environmental Protection Agency. Their labels specify that they are intended to kill clothes moths and other fabric pests, nothing else. Using any pesticide in a way not specified on its label is a violation of federal law. That means placing mothballs in attics, crawl spaces, gardens, or along baseboards to repel mice is technically an illegal use of the product.
This isn’t a technicality. The labeling restrictions exist because mothballs release toxic fumes that are only safe under the narrow conditions the label describes, typically inside a sealed container with clothing. When you smell mothballs, you are inhaling the insecticide itself. Used in open indoor spaces, those fumes build up in the air your family breathes.
Health Risks to People and Pets
Mothball fumes pose real health risks when used outside of a sealed garment bag or storage container. Naphthalene exposure has been linked to nasal cancer and other illnesses. A single mothball can cause serious harm if a small child eats one, and young children can easily mistake the small, round objects for candy or food.
Pets are also vulnerable. Dogs and cats can be poisoned by eating, inhaling, or even absorbing mothball chemicals through their skin. Cats are suspected to be more sensitive than other species. Naphthalene ingestion in animals almost always causes vomiting and loss of appetite first, and larger exposures can progress to a condition where red blood cells are destroyed, leading to pale gums, difficulty breathing, and in rare cases, seizures. Paradichlorobenzene, the other common active ingredient, primarily causes abdominal pain, vomiting, lethargy, and trembling. Chronic or repeated exposure to either chemical can damage the liver and kidneys.
Mothballs used outdoors carry additional risks: they can contaminate soil, plants, and water sources in your yard.
What Actually Works to Keep Mice Out
Effective mouse control comes down to three strategies: exclusion, sanitation, and trapping. Of these, exclusion (physically blocking mice from entering your home) delivers the most lasting results.
Seal Entry Points
Mice can squeeze through gaps as small as a dime. Walk your home’s exterior and look for cracks in the foundation, gaps around pipes and utility lines, spaces under doors, and openings where siding meets the foundation. Steel wool stuffed into small gaps works well because mice can’t chew through it. For larger openings, metal flashing or hardware cloth provides a permanent seal. The goal is to figure out how rodents are accessing the building and close those routes.
Remove Food and Water Sources
Mice aren’t picky eaters. They’ll feed on packaged food, crumbs in hard-to-clean areas, pet food left in bowls, compost, and even pet feces. Store pantry items in hard containers with tight lids. Clean up spills promptly, especially behind and under appliances. Don’t leave pet food out overnight. Taking away what attracted mice in the first place makes your home far less appealing than any repellent could.
Use Traps Strategically
Snap traps remain one of the most reliable tools for dealing with an active infestation. A major advantage of trapping over poison is that you know exactly where the mouse died, which avoids the problem of decomposing carcasses inside walls or ceilings. Place traps evenly spaced at first to identify where activity is highest, then concentrate traps in those zones.
If you’ve set traps but aren’t catching anything despite signs of activity, mice may have grown accustomed to them. Remove the traps for a few days, then reposition them in new spots. Make sure you’re using the right size: rat traps and mouse traps are different, and using the wrong one reduces your catch rate. For rats specifically, a technique called “prebaiting” helps overcome their natural fear of new objects. Place baited but unset traps and let the rats take the bait two or three times before actually setting the trigger.
Reducing the current population matters, but long-term prevention through exclusion and sanitation is the real goal. A home that offers no easy entry and no accessible food will stay mouse-free without relying on chemicals that don’t work or, in the case of mothballs, chemicals that put your household at risk.