Mothballs work by slowly releasing toxic fumes that poison and kill clothes moths, their larvae, and their eggs. The solid balls gradually turn into gas at room temperature, a process called sublimation, and when that gas builds up to a high enough concentration inside a sealed container, it’s lethal to fabric-eating insects. The key detail most people miss: mothballs only work in airtight spaces where the vapor can accumulate.
What’s Inside a Mothball
Mothballs sold in the U.S. contain very high concentrations of one of two chemicals: naphthalene or paradichlorobenzene. Both are solid at room temperature but slowly convert directly into gas without melting first. That’s why mothballs shrink over time rather than leaving behind a puddle. As the ball shrinks, the chemical vapors spread through the enclosed space.
Naphthalene is the older, more traditional ingredient and has a stronger, more persistent smell. Paradichlorobenzene is the more common choice in modern products. It works the same way but is generally considered slightly less toxic to humans. Both chemicals damage cells and tissues when inhaled in sufficient concentrations, which is what makes them effective against insects and dangerous when misused.
Why Airtight Containers Matter
This is the part most people get wrong. Mothballs are designed to be placed inside a tightly sealed container, like a storage bin with a locking lid or a garment bag that zips completely shut. The vapor needs to build up to a lethal concentration inside that enclosed space. If you toss mothballs into an open closet or a loosely closed box, the fumes simply disperse into the surrounding air. The concentration never gets high enough to kill moths, so you get all the smell and health risk with none of the pest control.
Labels on mothball products specify this clearly, and using them any other way is technically illegal under EPA regulations. Mothballs are classified as pesticides, and the label is a legal document that dictates exactly how the product can be used.
How the Vapors Kill Insects
When naphthalene or paradichlorobenzene gas reaches a high enough concentration, it’s toxic to clothes moths at every life stage. The vapors damage cells and tissues on contact, killing adult moths, larvae, and eggs. Larvae are the real target here, since adult moths don’t actually eat fabric. It’s the larvae that chew through wool, silk, cashmere, and other protein-based fibers. The gas penetrates through folds of clothing and reaches insects hiding deep in stored garments, which is an advantage over surface sprays.
Health Risks for People
The same properties that make mothballs lethal to insects also make them harmful to humans. Breathing in naphthalene vapors can cause headaches, nausea, dizziness, and vomiting. At higher or more prolonged exposures, naphthalene causes hemolytic anemia, a condition where red blood cells break apart and can no longer carry oxygen properly. Kidney and liver damage can also occur.
Children are especially vulnerable. Small children who have eaten mothballs have developed fever, abdominal pain, and discolored urine. Even indirect contact is a risk: infants have developed anemia from wearing clothes, diapers, or blankets that were stored with mothballs and not washed afterward. People with a certain inherited enzyme deficiency face an even greater risk of anemia from naphthalene exposure.
Both the World Health Organization and the U.S. EPA classify naphthalene as a possible human carcinogen based on animal studies. This is one reason the fumes should never be allowed to accumulate in living spaces.
Risks to Pets
Mothballs are dangerous for dogs and cats, and cats are suspected to be more sensitive than other animals. A pet that chews or swallows a mothball can experience vomiting, loss of appetite, abdominal pain, and lethargy. With larger exposures to naphthalene, pets can develop anemia, pale gums, difficulty breathing, and in rare cases, tremors or seizures. Paradichlorobenzene ingestion can lead to liver and kidney damage with repeated exposure. If a pet gets into mothballs, it’s a veterinary emergency requiring decontamination as quickly as possible.
Common Misuses
One of the most widespread misuses is scattering mothballs outdoors to repel snakes, squirrels, or other wildlife. This is illegal, ineffective, and harmful. The vapors disperse immediately in open air, so they never reach a concentration that would deter anything. Meanwhile, the chemicals contaminate soil, plants, and water, and pose a poisoning risk to children and animals who find them.
Another common mistake is placing mothballs in non-airtight containers like cardboard boxes, dresser drawers, or open closets. This exposes everyone in the home to low-level fumes over weeks or months without actually protecting the clothing inside. Some mothballs sold online or in informal markets may be illegal imports that haven’t been evaluated for safety or proper labeling, making them an unknown risk.
Removing Mothball Odor From Clothing
Mothball smell clings to fabrics because the chemicals absorb into the fibers. Washing stored clothing before wearing it is essential, not optional, especially for anything that will touch a baby’s skin. For stubborn odors, try airing garments outdoors in direct sunlight for several days. A wash cycle with white vinegar added to the rinse can help neutralize the smell. For storage furniture like cedar chests that absorbed the odor, lightly sanding the interior wood, then ventilating for a couple of weeks, often works. Placing activated charcoal inside a closed chest or container for several days can also absorb lingering fumes.
Safer Alternatives
Cedar is the most popular natural alternative. Cedar wood contains oils that repel moths, and cedar balls, blocks, or chips placed among stored clothing can help deter them. The oils do lose potency over time, but lightly sanding cedar items or adding a few drops of cedarwood essential oil refreshes the effect. Cotton balls with cedarwood oil tucked into drawers or garment pockets serve the same purpose.
Pheromone traps are another option. These use a synthetic version of the scent female moths produce to attract males, trapping them on a sticky surface. They won’t kill larvae already in your clothes, but they can reduce the breeding population and help you monitor whether you have an active infestation. For high-value garments, sealed vacuum storage bags eliminate the need for any chemical by simply removing the air moths need to survive.