Mothballs are called mothballs because that’s exactly what they are: small balls designed to repel and kill moths. The term first appeared in English in 1891, combining “moth” (the pest they target) with “ball” (their shape). It’s one of those rare product names that is purely, satisfyingly literal.
The Name Is Simply Descriptive
According to the Online Etymology Dictionary, the word “mothball” entered the language in 1891 as a compound of “moth” and “ball,” defined as a “naphthalene ball stored among fabrics to keep off moths.” There’s no clever inventor’s name behind it, no brand that got genericized, no foreign loan word. Manufacturers pressed a moth-killing chemical into a compact spherical shape, and people called it what it was.
The ball shape served a practical purpose. A sphere has a relatively low surface area compared to its volume, which means the chemical inside releases its fumes slowly and steadily over weeks or months. That slow, consistent release was ideal for protecting stored clothing in trunks and closets. Mothballs also come in flakes and crystal forms, which release their vapors faster because of their greater surface area. But the ball version became the iconic form, and its name stuck as the catch-all term for all moth-repellent products of this type.
The Moth They Were Made For
The “moth” in mothball refers specifically to the clothes moth, a small, pale insect that lays its eggs on natural fabrics like wool, silk, and fur. It’s not the adult moth that does the damage. The larvae feed on the protein fibers in these materials, chewing holes through sweaters, blankets, and coats, especially items stored in dark, undisturbed spaces for long stretches. By the late 1800s, when mothballs got their name, people were looking for a reliable way to protect seasonal clothing packed away in trunks and wardrobes.
How Mothballs Actually Work
Mothballs work through a process called sublimation, where a solid slowly converts directly into a gas without melting into liquid first. This is why mothballs shrink over time and eventually disappear entirely. As the ball turns to vapor, it fills an enclosed space (like a sealed garment bag or storage trunk) with fumes toxic to moth larvae and eggs.
The two chemicals historically used are naphthalene, a compound derived from coal tar, and paradichlorobenzene, a synthetic alternative. Both produce a heavy, pungent vapor that’s unmistakable to anyone who’s opened a grandmother’s closet. That distinctive smell comes from the same gas doing the pest-killing work. In a properly sealed container, the concentration builds high enough to be lethal to insects. In an open room, the vapors dissipate too quickly to be effective, which is why mothballs only work in enclosed spaces.
Why the Smell Lingers
The infamous mothball odor clings to fabrics because the chemical vapors don’t just float around clothing. They absorb into the fibers themselves. Naphthalene in particular bonds readily to textiles, and because it sublimated slowly into those fibers over months, it takes considerable effort to get it back out. Airing garments outdoors, washing them, or running them through a dryer cycle can help, but heavily treated items sometimes carry a faint smell for a surprisingly long time.
Health Concerns Worth Knowing
Mothballs aren’t just toxic to insects. Breathing in their fumes can cause headaches, nausea, vomiting, and confusion in humans. A CDC report documented a case in Indiana where a woman, her young daughter, and seven relatives across multiple households all developed symptoms including anemia, abdominal pain, and kidney problems from extensive mothball use indoors. People vary widely in their sensitivity to naphthalene exposure, and even small amounts have triggered reactions in susceptible individuals.
The EPA has linked naphthalene to nasal cancer and flagged the widespread sale of unregistered mothball products as a particular concern. Young children are especially at risk because mothballs can look like candy or toys. Any mothball product sold legally in the United States must carry an EPA registration number on its label, and the label directions are legally binding. Using mothballs outdoors, scattering them in gardens, or placing them in open rooms are all violations of their labeled use, and they’re ineffective in those settings anyway since the vapors can’t concentrate enough to work.
The name “mothball” has outlasted many of the situations it was coined for. Synthetic fabrics, which moths have no interest in, dominate modern wardrobes. Cedar blocks, lavender sachets, and airtight vacuum bags have replaced chemical mothballs in many homes. But for anyone storing heirloom wool or natural-fiber textiles long term, the original product and its perfectly straightforward name remain in use.