Mothballs are small balls of compressed chemical pesticide, made primarily from one of two industrial chemicals: naphthalene or paradichlorobenzene. Both are derived from petroleum and coal tar processing, not from any natural “moth” source. They work by slowly converting from a solid into a gas (a process called sublimation), filling an enclosed space with fumes that kill moths and their larvae.
The Two Chemicals Inside Mothballs
Naphthalene is the older of the two ingredients and was first registered as a pesticide in the United States in 1948. It’s a byproduct of coal tar distillation, the thick liquid left over when coal is heated to produce coke for steelmaking. Crude coal tar contains roughly 10% naphthalene, which is extracted, purified into white crystals, and then pressed into the familiar round pellets.
Paradichlorobenzene (sometimes written as para-dichlorobenzene or PDCB) is synthesized from benzene using chlorine gas. It became the more common mothball ingredient starting in the mid-20th century because it’s slightly less flammable than naphthalene and has a somewhat less pungent odor. Both chemicals are toxic to humans, and both produce the sharp, distinctive smell most people associate with mothballs.
From a manufacturing standpoint, the process is straightforward. The purified chemical is melted, poured into molds, and cooled into uniform spheres or cakes. Because the products contain at least 98% active ingredient, there’s very little else in a mothball besides the pesticide itself.
How Mothballs Actually Work
Mothballs are designed to protect stored clothing and textiles from clothes moths, specifically the larvae that feed on natural fibers like wool, silk, and fur. The adult moths themselves don’t eat fabric. They lay eggs on it, and the hatching larvae do the damage.
As a mothball sublimes, it releases a heavy vapor that fills an enclosed container (a sealed garment bag, a tightly closed trunk, or a storage bin). The concentration of gas builds up enough to kill both moth eggs and larvae. This only works in a confined space. Mothballs left in an open closet or scattered around a room won’t reach high enough concentrations to kill anything. They’ll just fill your living space with toxic fumes.
Health Risks of Exposure
Both naphthalene and paradichlorobenzene are genuinely toxic, and using mothballs outside of sealed containers creates real health risks. A CDC investigation documented a case where a woman distributed 300 to 500 mothballs throughout her apartment in open areas like the kitchen and living room. She, her 4-year-old daughter, and seven relatives in other households using mothballs the same way all developed symptoms: headaches, nausea, vomiting, abdominal pain, confusion, anemia, and kidney problems. All symptoms resolved once the mothballs were removed.
Naphthalene inhalation can cause skin and eye irritation, gastrointestinal distress, neurological symptoms including confusion and convulsions, kidney damage, and a type of severe anemia where red blood cells break apart. People with a genetic condition called G6PD deficiency (common in people of African, Mediterranean, and Southeast Asian descent) are especially vulnerable to this blood cell destruction, even at lower exposure levels.
The range of individual sensitivity is wide. Some people develop symptoms from casual exposure while others tolerate more. This unpredictability is one reason health agencies recommend using mothballs only as directed: in sealed containers with stored clothing, never as general air fresheners or pest control in living spaces.
What Happens When They Enter the Environment
Naphthalene doesn’t persist in the environment forever, but it doesn’t vanish instantly either. In soil and sediment, bacteria break it down with a half-life of roughly 2.5 to 4.5 weeks depending on the environment. Soil that’s been previously exposed to petroleum products breaks naphthalene down faster because it already hosts larger populations of hydrocarbon-eating bacteria. Pristine environments take longer. Paradichlorobenzene is more persistent and can contaminate groundwater when mothballs are improperly disposed of in yards or gardens.
Natural Alternatives That Came First
Before synthetic mothballs existed, people used cedar wood, lavender, and various herbs to protect stored textiles. These aren’t just folk remedies. Cedar wood contains several active compounds that genuinely repel and can even kill clothes moths.
The most important is cedrol, which makes up about 15% of cedar essential oil. Concentrations as low as 4% are toxic to clothes moth larvae. Other compounds in cedar, including thujopsene and cadinene, work by overwhelming moths’ ability to detect the pheromones they use to find mates and egg-laying sites. Red cedar is particularly potent, containing up to 10 times more essential oil per weight than other conifers like pine or fir.
Lavender, rosemary, cloves, bay leaves, and peppermint also have mild moth-repelling properties thanks to compounds like linalool, camphor, eugenol, and menthol. The drawback is that these botanicals tend to lose their effectiveness quickly as the oils evaporate, while cedar maintains its repellent properties over longer periods. Sanding the surface of cedar blocks or adding fresh cedar oil restores their potency. None of these natural options match the outright killing power of chemical mothballs in a sealed container, but for prevention in regularly accessed closets and drawers, they’re a safer choice that works well enough for most situations.