Mothballs are toxic to humans, pets, and the environment. They contain pesticide chemicals designed to kill insects, and those same chemicals can cause serious harm when inhaled, swallowed, or absorbed through the skin. The two active ingredients, naphthalene and paradichlorobenzene, are both classified as possible carcinogens by the International Agency for Research on Cancer.
What’s Actually in a Mothball
Mothballs are made from one of two chemicals: naphthalene or paradichlorobenzene. Both are solid at room temperature but slowly convert into gas through a process called sublimation. That distinctive mothball smell? It’s pesticide vapor filling the air around you. Inside a sealed container, the concentration of gas is high enough to kill moths and their larvae. But when mothballs are used in open spaces like closets, rooms, or attics, those fumes spread and linger at levels that can affect anyone breathing them in.
How Naphthalene Harms the Body
Naphthalene is the more dangerous of the two chemicals. It generates reactive molecules in the body that damage cell membranes and DNA. The most concerning effect is the destruction of red blood cells, a condition called hemolytic anemia. When red blood cells break down faster than the body can replace them, you lose the ability to carry oxygen efficiently. Symptoms include fatigue, dark-colored urine, pale skin, and shortness of breath.
Naphthalene also converts the oxygen-carrying protein in your blood into a form that can’t deliver oxygen to tissues. This can cause a bluish tint to the skin and lips even when blood oxygen readings appear normal. Breathing naphthalene fumes over a period of time, not just a single large exposure, can cause poisoning.
Risks From Paradichlorobenzene
Paradichlorobenzene is sometimes marketed as the “safer” mothball ingredient, but it carries its own risks. It irritates the eyes and respiratory tract on contact. At high concentrations, whether inhaled or swallowed, it can damage the liver. The liver processes this chemical into reactive byproducts that directly injure liver cells.
Long-term exposure has been linked to skin discoloration and anemia in humans. In animal studies conducted by the CDC’s toxic substances division, lifetime exposure to paradichlorobenzene caused liver cancer in mice through both inhalation and oral routes. Both naphthalene and paradichlorobenzene carry the same IARC classification: Group 2B, meaning they are “possibly carcinogenic to humans.”
People at Higher Risk
Some people are far more vulnerable to mothball exposure than others. The most significant risk factor is a genetic condition called G6PD deficiency, which affects roughly 400 million people worldwide and is especially common in people of African, Mediterranean, Middle Eastern, and Southeast Asian descent. People with this condition lack an enzyme that protects red blood cells from oxidative damage. Even modest exposure to naphthalene can trigger severe, rapid red blood cell destruction in these individuals.
Young children face elevated risk for a simpler reason: mothballs can look like candy or toys. A single mothball contains enough chemical to harm a small child if swallowed. Children also breathe faster relative to their body weight, so they inhale proportionally more fumes in the same room. Pregnant women should also avoid exposure, as naphthalene crosses the placenta.
Mothballs and Pets
Dogs and cats can be poisoned by mothballs through ingestion, inhalation, or even skin contact. Cats are suspected to be more sensitive than other species. Naphthalene irritates the digestive tract, so vomiting and loss of appetite are typically the first signs. If the exposure is large enough, pets can develop the same red blood cell destruction seen in humans, along with pale gums and difficulty breathing. In rare cases, neurological symptoms appear: trembling, loss of coordination, and seizures.
Paradichlorobenzene exposure in pets looks slightly different. It primarily causes abdominal pain, vomiting, lethargy, and trembling. Repeated or large doses can lead to liver and kidney damage. While a single small exposure to paradichlorobenzene is less likely to cause blood abnormalities right away, chronic exposure has been linked to anemia in animals.
Common Misuses That Increase Exposure
Mothballs are registered pesticides, and their labels specify use only in airtight containers with clothing. In practice, people use them in ways that dramatically increase toxic exposure. Scattering them in attics, basements, or crawl spaces to repel mice, snakes, or squirrels is both illegal (it violates EPA labeling requirements) and ineffective. Placing them in open closets, garages, or garden beds lets fumes accumulate in living spaces at concentrations never intended for continuous breathing.
Some people place mothballs under furniture or in rooms to “freshen” the air, not realizing the smell is literally toxic gas. Others put them in children’s clothing drawers or blanket storage without airtight containers, creating ongoing low-level exposure. If you can smell mothballs, you are inhaling pesticide vapor.
What to Do if Someone Is Exposed
If a child or adult swallows a mothball, or if someone has been breathing heavy mothball fumes in an enclosed space and feels unwell, call Poison Control at 1-800-222-1222 (in the U.S.) or your local emergency number. Don’t wait for symptoms to appear after ingestion, particularly with naphthalene, because red blood cell damage can develop over the following 24 to 48 hours. Move anyone experiencing fume exposure to fresh air immediately.
For pets, contact your veterinarian or an animal poison control hotline right away. Vomiting after mothball ingestion is common in dogs and cats but does not mean the danger has passed.
Safer Ways to Protect Clothing From Moths
Several non-toxic options can help keep moths away from stored clothing, though none are quite as lethal to insects as chemical mothballs. Lavender works as a deterrent: moths dislike the scent, so lavender sachets in drawers and wardrobes help keep them at bay. It won’t kill moths already present, but it discourages new ones from settling in.
Cedar is a step up in effectiveness. Cedar wood contains a natural oil that can kill small moth larvae. Cedar blocks, balls, or hanging tags placed in drawers and closets provide protection, though they lose potency after a few years and need to be refreshed with cedar essential oil. The most reliable non-chemical approach combines cedar or lavender with good storage habits: washing or dry-cleaning clothes before storing them (moths are attracted to body oils and food residue), using airtight garment bags or sealed plastic bins, and vacuuming storage areas regularly to remove eggs and larvae.