Mothballs do not work as a rat repellent, and using them for that purpose is both ineffective and illegal. Mothballs are registered by the EPA exclusively to kill clothes moths and their eggs inside sealed containers like garment bags and storage closets. They are not designed, tested, or approved for use against rats, mice, snakes, or any other wildlife.
Why Mothballs Don’t Repel Rats
Mothballs sold in the U.S. contain one of two chemicals: naphthalene or paradichlorobenzene. Both work by releasing fumes that build up inside airtight spaces, reaching concentrations high enough to kill small insects like clothes moths. The key phrase is “airtight spaces.” Scattered on a floor, in a crawlspace, or around the outside of a house, the vapors dissipate too quickly to reach a concentration that would bother a rat, let alone drive one away.
Rats are also far larger and more resilient than moths. Even in partially enclosed spaces, the amount of mothballs you’d need to produce a meaningful vapor concentration would create a serious health hazard for you, your family, and your pets long before it deterred a rat. There is no scientific evidence that mothballs repel rodents at any concentration safe for human habitation.
It’s Illegal to Use Them This Way
Mothballs are a registered pesticide product, and every pesticide label carries the force of federal law. Using a pesticide in a way that contradicts its label, commonly called “off-label use,” is a violation of federal pesticide regulations. The label on mothball packaging specifies use only inside sealed garment bags, storage closets, and airtight containers for the control of clothes moths. Scattering them in attics, basements, gardens, or anywhere else to repel rats is not a gray area. It is explicitly not an approved use.
Health Risks of Misusing Mothballs
When you smell mothballs, you are inhaling the pesticide. That’s exactly how the product works: it turns from a solid into a gas. In a sealed garment bag, this is controlled. In an open living space, you and everyone in your household breathe it in continuously.
Naphthalene vapor exposure causes headaches, nausea, dizziness, and vomiting. At higher or prolonged exposures, it can trigger hemolytic anemia, a condition where red blood cells break apart and can no longer carry oxygen properly. People with a common inherited enzyme deficiency (affecting hundreds of millions of people worldwide) face a much higher risk of this reaction. The EPA has classified naphthalene as a possible human carcinogen based on animal studies.
Children are especially vulnerable. Small children who have eaten naphthalene mothballs developed diarrhea, fever, abdominal pain, and painful urination with discolored urine. Even indirect exposure is dangerous: infants have developed anemia simply from wearing clothing or being wrapped in blankets that were stored with mothballs and not washed afterward. Pregnant women who inhaled mothball vapors or ingested mothballs gave birth to babies with hemolytic anemia.
Pets are at serious risk too. Dogs that have eaten naphthalene mothballs show lethargy, vomiting, diarrhea, loss of appetite, and tremors. A mothball scattered on the ground is easily within reach of a curious dog or cat.
Outdoor Use Contaminates Soil and Water
Placing mothballs outside, whether around a foundation, in a garden, or near entry points, introduces pesticide chemicals directly into the environment. The National Pesticide Information Center warns that mothballs used outdoors can contaminate soil, plants, and water. This means chemicals leaching into garden beds where you grow food, into groundwater, and into areas where children and pets play. The environmental harm adds to the personal health risks with zero benefit against rats.
What Actually Works Against Rats
Effective rat control relies on three strategies used together: inspection, exclusion, and sanitation. Skipping any one of them usually leads to the problem returning.
Inspection
Start by figuring out where rats are entering, where they’re nesting, and why they’re attracted to your property. Look for droppings, gnaw marks, grease trails along walls, and gaps in your building’s exterior. Correctly identifying whether you have rats or mice matters because the two require different trap sizes and slightly different approaches.
Exclusion
Sealing entry points is the single most important long-term solution. Rats can squeeze through gaps smaller than you’d expect. Steel wool packed into holes, metal flashing over larger openings, and door sweeps on exterior doors all help block access. This is the step that prevents new rats from replacing the ones you remove.
Trapping
Traps are effective and have a practical advantage over poison: you know exactly where the rat died, so you avoid the problem of a carcass decomposing inside a wall or ceiling. Place traps evenly spaced along walls and in areas with signs of activity. Rats are naturally cautious around new objects, a behavior called neophobia. To overcome this, bait your traps but don’t set them for the first few rounds. Let rats take the bait freely two or three times before arming the trigger. If traps stop catching anything despite ongoing signs of activity, remove the traps for a few days, then reposition them in new locations. Rodents learn to avoid familiar traps.
Sanitation
Rats stay where they find food and water. Removing those resources makes your property far less attractive. This means cleaning up spills in hard-to-reach spots, storing food (including pet food) in sealed containers, not leaving pet food bowls out overnight, securing trash and compost bins, and fixing leaky pipes or eliminating standing water. Even condensation from refrigerator motors or water pipes can sustain a rat population. Rats are not picky eaters. They’ll feed on packaged food, pet feces, compost, and crumbs behind appliances.
Combining all three approaches, blocking entry, trapping the rats already inside, and eliminating what attracted them, is the standard integrated pest management strategy recommended by university extension programs and public health agencies. It takes more effort than tossing mothballs around, but it actually solves the problem.