Mothballs do not effectively repel rats. Despite being a widely shared home remedy, mothballs were designed to kill clothes moths in sealed containers, and they lack the potency to drive rodents away from an area. The active chemicals in mothballs, naphthalene and paradichlorobenzene, produce fumes that are toxic to small insects in enclosed spaces but do not reach concentrations strong enough to deter rats in open or semi-open environments like attics, crawl spaces, or garages.
Why Mothballs Don’t Work on Rats
Mothballs work by slowly releasing toxic vapor inside a sealed container, such as a garment bag or airtight storage bin. That enclosed space allows fumes to build up to levels lethal to moths and their larvae. When you scatter mothballs in an attic, shed, or along a foundation, the vapor disperses into the open air far too quickly to reach a concentration that would bother a rat. Rats are also significantly larger than insects and can simply avoid or tolerate the smell.
To produce fumes strong enough to affect a rat, you would need an enormous quantity of mothballs in a tightly sealed space. At that point, the fumes would be far more dangerous to you and your family than to the rodents. A CDC investigation in Indiana documented a household that had distributed 300 to 500 mothballs throughout an apartment for pest and odor control. The residents, including a 4-year-old child, developed headaches, nausea, vomiting, abdominal pain, confusion, anemia, and kidney problems from naphthalene exposure. Their symptoms resolved only after the mothballs were removed.
Health Risks to People and Pets
Breathing naphthalene fumes can cause a range of symptoms: skin and eye irritation, nausea, vomiting, diarrhea, confusion, and in severe cases, seizures, kidney failure, and a dangerous breakdown of red blood cells. People with a common inherited enzyme deficiency (affecting roughly 400 million people worldwide) are especially vulnerable to this blood cell destruction.
Pets face serious risks too. Cats are suspected to be more sensitive than other animals. Dogs and cats that ingest or are chronically exposed to mothballs can develop vomiting, loss of appetite, abdominal pain, and lethargy. Larger exposures can progress to anemia, difficulty breathing, pale gums, tremors, and seizures. Camphor-based mothballs are the most toxic of the three common formulations, followed by naphthalene, then paradichlorobenzene.
Using Mothballs This Way Is Illegal
Mothballs are EPA-regulated pesticides, and their labels specify exactly where and how they can legally be used. That means sealed containers for fabric storage, nothing more. Using mothballs to repel rats, snakes, squirrels, or any other animal not listed on the label is a violation of federal pesticide law. Beyond the legal issue, scattering them outdoors introduces toxic chemicals into soil and groundwater. Naphthalene can pass through certain soil types and reach the water table before bacteria have a chance to break it down.
What Actually Works Against Rats
Effective rat control relies on three strategies used together: cutting off their entry points, removing what attracts them, and using targeted control methods when needed.
Seal Entry Points
A rat can squeeze through a gap as small as half an inch, roughly the width of your thumb. Mice need even less, just a quarter-inch opening, about the diameter of a pencil. Warm air and food smells escaping through these gaps act like a beacon to rodents. Walk the perimeter of your home and check foundations, walls, rooflines, and where pipes or wires enter the building. Seal openings with steel wool, hardware cloth (with mesh smaller than half an inch), metal flashing, or cement. Rats can chew through caulk, spray foam, and wood, so use materials they can’t gnaw through. If rats are entering through floor drains, cover them with fine hardware cloth.
Eliminate Food and Shelter
Store all food, including pet food and birdseed, in thick plastic or metal containers with tight lids. Keep garbage cans sealed. Clean up fallen fruit from trees. Move firewood and debris piles away from the house, since these provide nesting sites. Trim tree branches that overhang or touch your roof, as roof rats use these as highways into attics.
Use Targeted Control Methods
Snap traps remain one of the most effective tools for killing rats that are already inside. Place them along walls and in areas where you see droppings, grease marks, or gnaw damage. Bait stations with rodenticide are another option, though they carry risks to children, pets, and wildlife and are best handled by a licensed pest control professional. For persistent infestations, professional service is often the fastest path to resolution, since experts can identify entry points and nesting areas you might miss.
The combination of exclusion and sanitation is the foundation of any lasting solution. Killing individual rats without sealing their entry points and removing attractants just creates a vacancy that new rats will fill within weeks.