Is Smelling Naphthalene Balls Harmful?

Breathing in the fumes from naphthalene mothballs is genuinely harmful, and the risk increases with the concentration of vapor and the duration of exposure. Naphthalene, the chemical responsible for that sharp, unmistakable mothball smell, is classified by the International Agency for Research on Cancer as possibly carcinogenic to humans and by the U.S. National Toxicology Program as reasonably anticipated to be a human carcinogen. Beyond cancer concerns, inhaling naphthalene vapor can trigger a cascade of blood-related damage, particularly in people with certain genetic traits they may not even know they carry.

What Naphthalene Does Once You Breathe It In

When you inhale naphthalene fumes, the chemical enters your bloodstream through your lungs and travels to the liver, where it gets broken down into compounds called naphthoquinones. These byproducts generate reactive oxygen species that attack red blood cells, converting the iron in hemoglobin from a form that carries oxygen to a form that cannot. The result is a condition called methemoglobinemia, in which your blood progressively loses its ability to deliver oxygen to your tissues. At the same time, the oxidative stress destabilizes the membranes of red blood cells, causing them to rupture and release their contents into the bloodstream, a process known as hemolytic anemia.¹

This is not just a theoretical concern from animal studies. Clinical case reports document patients developing dark brown urine, watery diarrhea, vomiting, fever, rapid heart rate, and dangerously low blood pressure within two to four days after significant naphthalene exposure. A telling sign is that pulse oximetry readings can get stuck around 84-85% even when supplemental oxygen is being given, because the methemoglobin in the blood confuses the sensor.²

Most of the severe poisoning cases reported in medical literature involve ingestion rather than inhalation alone. But inhalation is still recognized as a legitimate route of toxic exposure, and the same blood-damaging mechanism applies regardless of how the naphthalene enters the body. The difference is primarily one of dose: swallowing a mothball delivers a concentrated hit, while breathing fumes delivers a smaller but sustained dose over hours or days.

Why Some People Are Far More Vulnerable

The single biggest risk factor for severe naphthalene poisoning is a genetic condition called G6PD deficiency. People with this enzyme deficiency lack the ability to produce enough of a protective molecule that shields red blood cells from oxidative damage. Without that shield, the oxidative assault from naphthalene metabolites hits much harder, and hemolytic anemia can become severe enough to cause organ failure.³

G6PD deficiency is one of the most common enzyme deficiencies in the world, affecting an estimated 400 million people globally, with especially high prevalence in populations from Africa, the Mediterranean, the Middle East, and Southeast Asia. Many carriers have no idea they have it because the condition often produces no symptoms until they encounter an oxidative trigger. Naphthalene is one of those triggers, and it can be the first time a person or family learns about the deficiency, usually in a hospital emergency room.

Children with G6PD deficiency are at particular risk for more pronounced symptoms and worse outcomes from naphthalene exposure.⁴ But even without G6PD deficiency, young children are more vulnerable than adults because of their smaller body mass, higher respiratory rate relative to body size, and tendency to put things in their mouths. Naphthalene mothballs look and feel similar to candy or mints, and reports describe children accidentally sucking or chewing on them.⁵

Risks to Newborns and Pregnant Women

Naphthalene exposure during pregnancy deserves its own consideration because the chemical can cross the placenta. In at least one documented case, a mother who used naphthalene mothballs throughout the second and third trimesters delivered a newborn who developed severe complications including dangerously high bilirubin levels requiring exchange transfusion, hemolytic anemia, pulmonary hypertension, respiratory failure, and kidney failure.⁶

Neonates are especially susceptible to the oxidative effects of naphthalene because their bodies have low stores of the protective antioxidant glutathione and because their liver enzymes are still immature. This combination means a newborn’s system is poorly equipped to neutralize the toxic metabolites that form when naphthalene is processed by the body. For pregnant women who store clothes in naphthalene mothballs and regularly handle or breathe in the fumes, the exposure can become chronic enough to affect the developing baby even if the mother herself feels fine.

Chronic Inhalation and Cancer Risk

Short, occasional whiffs of mothball odor are a very different exposure from living in a home where naphthalene mothballs are placed in open containers, closets, or storage areas and left to sublimate continuously. Using naphthalene as a pest repellent or deodorant, particularly in enclosed indoor spaces, can produce some of the highest indoor concentrations measured.⁷ These concentrations matter because the health risks of naphthalene are dose-dependent, and people who live with constant low-level exposure build up a cumulative burden.

Animal studies have shown that even relatively low concentrations of naphthalene vapor damage the lining of the nasal passages. Rats exposed to naphthalene vapor over 90 days developed tissue changes in the nose including abnormal cell growth, degeneration and death of the cells responsible for the sense of smell, and a type of tissue remodeling called squamous metaplasia. Some of this damage persisted even four weeks after exposure ended.⁸

The cancer question is where things get serious for long-term inhalers. In two-year bioassays conducted by the National Toxicology Program, naphthalene exposure caused nasal tumors in both male and female rats and lung tumors in female mice. Based on these findings, the NTP classified naphthalene as “reasonably anticipated to be a human carcinogen,” while the IARC placed it in Group 2B, meaning “possibly carcinogenic to humans.” Both organizations noted that there was sufficient evidence from animal experiments but inadequate direct evidence in humans.⁹

The “inadequate evidence in humans” part is worth understanding. It does not mean naphthalene has been shown to be safe for humans. It means there have not been enough well-designed studies in human populations to definitively establish or rule out a cancer link. This gap exists largely because isolating naphthalene exposure from all the other chemical exposures in a person’s life is extremely difficult. The animal evidence, combined with the known tissue damage to the nose and lungs from chronic inhalation, is considered strong enough to warrant precaution.

The Other Kind of Mothball

Not all mothballs are naphthalene. Many products sold today contain paradichlorobenzene (PDCB) instead, and some people assume the switch makes them safe. It does not. PDCB is its own chemical with its own toxicity profile. It can damage the liver, kidneys, skin, lungs, and the central nervous system. Neurological effects from PDCB poisoning can include a condition called leukoencephalopathy, which involves the degeneration of the white matter of the brain, and a range of other neurological problems.¹⁰

Animal studies confirm that inhaling PDCB vapor causes liver toxicity in both mice and rats, with mice developing actual liver cell death at higher exposures. Male rats exposed to PDCB developed kidney damage through a specific mechanism involving protein accumulation in the kidney tubules, along with drops in red blood cell counts and hemoglobin levels.¹¹

There is also a behavioral dimension to PDCB mothball risk. Some individuals develop a compulsive habit of sniffing or even eating mothballs, a behavior sometimes linked to pica. Case reports describe patients with elevated blood levels of paradichlorobenzene and neurological changes from chronic mothball ingestion driven by this compulsion.¹² The takeaway is that switching from naphthalene to PDCB mothballs trades one set of health risks for a different but still concerning set. Neither chemical is something you want to breathe routinely.

How to Tell if You Have Been Exposed

If you live in a home that uses mothballs and want to know whether the chemical is accumulating in your body, there is a biomarker for that. Urinary naphthol levels are used to assess both occupational and environmental naphthalene exposure. However, this test has a quirk: one of the naphthol forms it measures is also a breakdown product of the insecticide carbaryl, which means your naphthol levels could be elevated from pesticide exposure that has nothing to do with mothballs.¹³ A healthcare provider would need to consider your full exposure picture to interpret the result meaningfully.

In a clinical emergency, the telltale signs of acute naphthalene poisoning are the combination of hemolytic anemia and methemoglobinemia. Blood work showing elevated bilirubin, falling hemoglobin, and methemoglobin levels, along with the characteristically dark brown urine, points strongly toward the diagnosis, especially if there is a history of mothball exposure in the household.²

Practical Steps to Reduce Your Risk

If you currently use naphthalene mothballs in your home, the most effective risk reduction is to stop using them entirely, particularly if children, pregnant women, or anyone with G6PD deficiency lives in or visits the home. For those who feel they need moth protection, several strategies can help without the toxic fumes:

• Cedar products: Cedar wood blocks, chips, and hangers contain natural oils that repel moths. They need occasional sanding or refreshing with cedar oil to maintain effectiveness.
• Lavender sachets: Dried lavender or lavender oil sachets placed among stored clothes act as a deterrent. Moths dislike the scent, and unlike naphthalene, it does not generate toxic metabolites in your body.
• Proper garment storage: Clean clothes before storing them, since moths are attracted to body oils and food stains. Seal clothes in airtight bags or containers, which physically prevents moth access and makes chemical repellents unnecessary.
• Temperature treatment: Freezing garments for several days kills moth larvae. This is especially useful for woolens and silks going into long-term storage.

Research into plant-based alternatives has shown some promise. Microencapsulated rosemary essential oil, for instance, maintained strong repellent activity against the Indian meal moth for up to 14 days in laboratory tests, while free rosemary oil lost effectiveness within a week.¹⁴ These plant-based options are still being refined for consumer use, but they point toward a future where effective moth repellents do not come with the health baggage of naphthalene or paradichlorobenzene.

The Problem With “Just a Little Smell”

One of the most common misunderstandings about naphthalene mothballs is that the smell itself is harmless and that danger only comes from eating them. This is wrong. The smell IS the chemical. Naphthalene is a solid that slowly converts directly to vapor at room temperature through a process called sublimation. When you smell mothballs, you are inhaling naphthalene molecules, and those molecules enter your lungs and bloodstream. The stronger the smell, the higher the concentration in the air, and the greater the dose your body is absorbing.

Another common misconception is that the risk disappears once you air out the clothes. While ventilation helps reduce the concentration of naphthalene vapor clinging to fabrics, the chemical can be surprisingly persistent in enclosed spaces. Indoor sources of naphthalene, particularly when mothballs are used excessively as general pest repellents rather than just for clothing storage, can produce the highest indoor naphthalene concentrations.⁷ Placing mothballs in open bowls around a room, scattering them in attics, or using them under sinks and in bathrooms, all of which are common practices in some households, exposes everyone in the home to continuous inhalation.

People also tend to underestimate how quickly they stop noticing the smell. Olfactory adaptation, the phenomenon where a persistent odor fades from awareness, can set in within minutes of continuous exposure. Once you stop smelling the mothballs, it is easy to believe the chemical is gone. It is not. Your nose has simply tuned it out while the vapor continues to fill the air and enter your lungs. This false sense of safety can lead people to tolerate much higher cumulative exposures than they realize.

When Mothballs Are Used as General Pest Control

In many cultures and households, naphthalene mothballs are not just for moths. They are placed around homes to repel snakes, rodents, insects, and even neighborhood cats. This widespread off-label use dramatically increases indoor concentrations because the mothballs are deployed in larger quantities, in open spaces, and often year-round rather than seasonally in sealed containers.

Environmental health professionals have flagged this pattern as a significant and underappreciated source of indoor naphthalene exposure. The practice turns a targeted product, designed to protect specific stored garments in sealed containers, into an ambient air contaminant affecting everyone in the household. Homes where mothballs are scattered generously as a general deterrent can have naphthalene air levels many times higher than homes where a few balls are sealed inside a garment bag. Children playing on floors near these exposed mothballs face both inhalation and hand-to-mouth ingestion risks simultaneously.

If you recognize this pattern in your own home or a relative’s home, replacing the naphthalene with targeted, non-toxic pest management is the most meaningful change you can make. For each pest type, there are specific alternatives that work without filling your living space with a probable carcinogen. Sealed food storage deters pantry moths and rodents. Physical barriers and caulking keep snakes and insects out. The naphthalene mothball, for all its cultural familiarity, was never designed for any of these jobs, and using it that way creates a genuine indoor air quality hazard.